ALBERT

Notes: The formation of complex between the Cu2+ ion and poly(α-L-glutamic acid) [poly(Glu)] in 150 mM NaCl solutions was studied by uv-visible absorption and equilibrium dialysis methods at the mixing ratios of Glu residues to Cu2+, R, of 32, 16, and 8 and in the pH range 4-7. The results showed that more than 90% of Cu2+ ions bind to the poly(Glu) at pH 〉 4.9, but the bound Cu(II) begins to dissociate with a decrease in pH. The absorption spectra of bound Cu(II) varied with pH and R in a complicated manner. Three different component spectra were disclosed from the analysis of the pH dependence of the bound spectra. We concluded that poly(Glu)-Cu(II) complexes fall into three classes in the pH range 4-7, with the proportions of these complexes varying with both pH and R. The three complexes predominate either in the helix or extended-coil region, in the helix-coil transition region, or in the helix-aggregate region. The stability constant and binding mode of each Cu(II)-Glu complex were estimated from the dialysis data. With these results, the possible structure of each complex is discussed.

Notes: The variable-temperature proton nmr spectra of the oligoribonucleotides in the series CpApX and the series ApGpX, X = A, G, C, U, together with the parent dimers CpA and ApG have been measured. A complete analysis of all the nonexchangeable base proton resonances and ribose H-1′ proton resonances was made. The presence of trends in the shielding abilities of the various bases at both the nearest-neighbor and next-nearest-neighbor positions were identified. The observed shieldings could be used to predict the chemical shifts of protons in related systems. Based on the empirical results from ribodinucleoside monophosphates, the temperature-dependent behavior of the J1′2′ coupling constants of the triribonucleotides suggested that the compounds in the CpApX series stacked from the 5′-end to the 3′-end, while those in the ApGpX series stacked from the 3′-end to the 5′-end.

Notes: Closed random Gaussian polygonal chains of N (6 〈 N 〈 150) bonds of equal length b and thickness d have been generated on a computer. The knot type, the writhing number w, the radius of gyration, and the average of the inverse of the distance between two apices have been determined for each chain. For all the studied knot types - 0, 31, 41, 51, and 52 - the probability density of finding a given w is Gaussian. The Gaussian is centered about 0 for the amphichiral knots. Therefore, for long circular DNAs, the contribution to the supercoiling energy, which depends on w only, may be considered as purely entropic and may be expressed as ARTw2/N, in agreement with previous semiempirical considerations. The parameter A increases with chain thickness, it decreases as N gets larger but rapidly reaches a plateau. Comparison with experimental data from the literature would suggest that the ratio of the writhing to the constraint increases with ionic strength. The ratio of sedimentation constant of the supercoiled DNA to the sedimentation constant of the nicked DNA varies as N1/4 (w/N)2, and therefore depends on the writhing density and on the length of the DNA.

Notes: A band-centrifugation method for the analysis of an assembly reaction of a simple virus from its RNA and protein is described. The experiment was carried out by sedimenting a band of viral RNA through a solution of depolymerized coat protein. The resulting radial distribution of the reaction products, followed as a function of time, was analyzed by a computer simulation of the series of reaction. This method is based on a numerical solution of the continuity equation for the sedimentation-diffusion process [Claverie, J.-M., Dreux, H. & Cohen, R. (1975) Biopolymers 14, 1685-1700; Cohen, R. & Claverie, J.-M. (1975) Biopolymers 14, 1701-1716]. A numerical method for the simulation of the chemical reaction is derived. From the simulated reaction series, equilibrium constants emerge for the successive addition of protein subunits to the growing nucleoprotein particle.The method is applied to the assembly of alfalfa mosaic virus. If the reaction between RNA and protein is carried out in 0.32M CsCl, pH 7.0, two stages during particle growth are resolved, each characterized by an equilibrium constant K. The determined values for K range from 5 × 105 to 3 × 106 l. mol-1. The existence of these two stages may have a structural implication in the assembly, as they likely represent an elongation and a termination stage. If the reaction is carried out under more favorable conditions (0.25M CsCl, pH 7.0), a kinetic constant of at least 105 l. mol-1 sec-1 is derived for each reaction step. Under these conditions the assembly appears to be completed within 1 min, which is too fast to detect distinct stages by band sedimentation.

Notes: Purified insoluble elastin samples labeled with [1-13C]valine, [1-13C]alanine, and [1-13C]-lysine were prepared from chick aorta in culture. The molecular mobility at the labeled sites was investigated using 13C-1H magnetic double-resonance spectroscopy. Linewidths, T1, and nuclear Overhauser effect (NOE) values of the labeled carbons alone were obtained from dipolar decoupled difference spectra. Analysis of these parameters together with signal intensity measurements showed that essentially all the valyl residues, ca. 75% of the alanyl residues, and ca. 60% of the lysyl residues were characterized by rapid backbone motions having τ = 65 nsec. Resonances due to the remaining alanyl and lysyl residues were detected in cross-polarization experiments, which enhance the signals of motionally restricted carbons. Since lysyl and alanyl residues are found in the crosslink regions of elastin, whereas valyl residues are not, we conclude that crosslinks rather than secondary structures in the extensible region of the protein are the main source of motional restrictions in the protein. Elastin chain mobility was monitored by linewidth measurements over the range -90 to +70°C. When the swelling solvent (0.15M NaCl) was fixed at 0.6 g/g of elastin, a rapid monotonic reduction in chain mobility was observed as the temperature was lowered from 50 to 5°C. Liquidlike mobility was completely lost at 5°C. In contrast, the same sample in contact with excess solvent retained its liquidlike molecular mobility until -13°C, where it abruptly became rigid. The molecular mobility of this sample was temperature insensitive in the physiologically interesting range, 20-40°C, as a consequence of the opposing influences of temperature and swelling. Taken together these nmr data indicate that under physiological conditions, elastin is a network of mobile chains whose motions are strongly influenced by protein-solvent interactions.

Notes: Preferential solvation of the glucans amylose, pullulan, and dextran in binary dimethyl-sulfoxide/water (DMSO/H2O) solvent mixtures has been measured using gel-permeation chromatography. The preferential solvation behavior of the three glucans in DMSO/H2O solvent mixtures is indistinguishable in the experiments reported. In solvent mixtures with mol ratio DMSO/H2O less than 1:2, all three glucans are solvated preferentially by H2O. The maximum extent of preferential solvation by H2O is about 2.5 mol H2O/mol of glucose residues. When the DMSO/H2O mol ratio exceeds 1:2, DMSO solvates the glucans preferentially to a maximum extent of about 1 mol DMSO/mol of glucose residues. An interpretation of the change in preferential solvation with mixed solvent composition is suggested in terms of the known characteristics of the binary solvent system, and the relationship of preferential solvation, reported here, to the absolute solvation of the glucan chains is discussed.

Notes: The dc electrical conductivity of large single crystals of hen egg-white lysozyme has been measured. The samples were grown from aqueous solution and dried in air with silica gel. The temperature dependence of the conductivity obeyed the relation σ = σ0 exp(- ΔE/kT), with ΔE = 1.2 eV. The ΔE value agreed with most of the previous results for various proteins in the form of lyophilized powder. On the other hand, log σ0, being between 7 and 11, was much larger than the previously reported values and differed among the samples. An irreversible decrease in σ0, without affecting ΔE, was observed on heating the samples above 85°C. It was shown that the set of results can be explained if the charge carriers responsible for the observed conduction are regarded as protons, originating from residual water molecules. Photoresponse of the samples to uv radiation below 305-315 nm was also observed. Reproducible and reliable results were obtained relatively easily in the present experiments, which is thought to be the main advantage of using single-crystalline samples.

Notes: A general formalism, which includes translation-rotation coupling, is proposed for calculating translational and rotational transport properties, as well as intrinsic viscosities, of rigid macromolecules with an arbitrary shape. This formalism is based on Brenner's theory of translational-rotational dynamics and on methods for the calculation of hydrodynamic properties that have been already presented, and can be regarded as a generalization of the one proposed by Nakajima and Wada. The calculated transport properties depend on the origin as predicted by Brenner's theory, but in a disagreement with him, the center of resistance and the center of diffusion do not coincide. As one can define several hydrodynamic centers, which in practice turn out to be located at different points, the influence of the choice of the center on the calculated transport properties is discussed. An analysis of the translation-rotation coupling effects in translational diffusion reveals that they arise exclusively from hydrodynamic interactions and are rather small in some cases of interest. Finally, we present a study of the rotational diffusion of rigid bent rods with a fixed length-to-diameter ratio. The diffusion coefficients obtained can be useful to estimate changes with respect to a straight rod.

Notes: As a model compound for the growing chain in the activated-NCA type of polymerization of α-amino acid N-carboxyanhydride (NCA), 3-[ω-acetylglycyl-poly(α-amino acid) acyl]-α-amino acid NCA (called the prepolymer) having various degrees of polymerization (DPs) was synthesized by the polymerization of Phe, Val, Glu(OEt), and Asp(OBzl) NCA in the presence of AcGly NCA by the tertiary amine. Activated (S)-Phe, Val, Glu(OEt), and Asp(OBzl) NCA were added to the terminal cyclic group of the corresponding (S)- or (R)- prepolymer, and the enantiomer selectivity in the reaction was investigated. With prepolymers having DPs ranging from 1 to 15, the addition reaction always took place preferentially between species having the same configuration, and the degree of the enantiomer selection increased with increasing DP of the prepolymer. With prepolymers having DP = 1 and 2, we found contributions from the chiral terminal unit and the chiral penultimate unit to the enantiomer selection, respectively. Prepolymer having DP = 5 was shown to take a β-type conformation, which led to higher enantiomer selection; and prepolymers having DP = 10 and 15 were shown to take an α-helix conformation, which led to much higher enantiomer selection than did the β-type conformation. In the present investigation the mechanisms of terminal-unit control, penultimate-unit control and conformational control of the enantiomer selection in the activated-NCA type of polymerization were clearly observed.

Notes: The helix-coil transition and conformational structure of poly(8-bromoadenylic acid) [poly(8BrA)] have been investigated using 1H- and 13C-nmr, CD, and ir spectroscopy. The results have been compared with the structure of the related 5′-mono- and polynucleotides. The chemical shifts of H(2′), H(3′), C(2′), and C(3′) nmr signals show an interesting correlation with both the puckering of ribose ring and glycosidic bond torsion angle. Poly(8BrA) shows an upfield shift of the C(3′) signal and a downfield shift of the H(3′) signal compared to the chemical shifts in poly(A). These shifts are consistent with a C(3′) endo-syn conformation for poly(8BrA). A similar effect has been reported previously and is also observed here on the C(2′) and H(2′) signals when the preferred conformation is C(2′)endo-syn (e.g., in 5′-8BrAMP). The chemical-shift parameters thus act as a probe for studying syn ⇄ anti and N ⇄ S equilibria in solutions. The three-bond 1H-′13C coupling constants between H(1′) and C(8) and C(4) have been measured in poly(8BrA) and 5′-8BrAMP and their structural implications have been discussed. The observed preference of a C(3′)endo-syn conformation for poly(8BrA), coupled with other evidence, throws doubt on the validity of a correlation previously reported whereby a syn conformation is associated with a C(2′)endo ribose pucker. The backbone conformation of randomly coiled poly(8BrA) is very similar to the structures found in polyribonucleotides: poly(A) and poly(U). All three polymers show strong preferences for the backbone angles found in RNA helices. The CD spectrum of poly(8BrA) has a striking relationship to that of poly(A). The signs of all extrema are inverted, and the magnitudes are related by a constant factor. We suggest that these differences result from a change in the angle between coupled transition moment vectors in the two polymers. Infrared spectra of poly(8BrA) in H2O and D2O solution are reported for the frequency range below 1400 cm-1. The antisymmetric 〉PO2- stretching vibration is observed at an unusually low frequency in the helix (1214 cm-1). The symmetric 〉PO2- stretch occurs at ∼1095 cm-1 but is not resolved from a ring vibration near this frequency. A conformationally sensitive band, characteristic of helical RNA structures, is observed at 817 cm-1 and disappears when the helix is melted. This observation confirms the conclusion that ordered poly(8BrA) has a regular helical structure with an RNA backbone conformation. A stereochemical explanation is provided for the failure of poly(8BrA) (or other syn polymers) to form double helices with anti-polyribonucleotides.

Notes: The arginine and lysine residues of calf thymus histone H1 were modified with large molar excesses of 2,3-butanedione and O-methylisourea, respectively. Kinetic study of the modification reaction of the arginine residue revealed that the reaction is divided into the two pseudo-first-order processes. About a third (1 Arg) of the total arginine residues of the H1 molecule was rapidly modified without causing any detectable structural change of the molecule, and the slow modification of the remaining arginine residues (2 Arg) led to a loss of the folded structure of H1. In the case of lysine residue modification, 93% (56 Lys) of the total lysine residues of the H1 was modified with the same rate constant, while 7% (4 Lys) of lysine residue remained unmodified. When the reaction was performed in the presence of 6M guanidine-HCl, all of lysine residues were modified. It is concluded that the 2 arginine and 4 lysine residues resistant to modification are buried in interior regions of the H1 molecule and play an important role in the formation of the H1 globular structure, while the other 1 arginine and 56 lysine residues are exposed to solvent.

Notes: The molar Kerr constants mK, molar refractions mR, and dipole moments μ are reported for the N-methylacetamides CX3CONHCH3 (X = H, CH3, F. CI, Br) and acetamides CX3CONH2 (X = H, F, Cl, Br). The components of the polarizability tensor α are deduced for N-methylacetamide and acetamide on the basis of the bond additivity approximation. This α is found to be considerably more anisotropic than was indicated in previous determinations by other methods. The data for N-methylacetamide were used to calculate mK, μ, and γ2 (anisotropy squared) of N-acetyl-N′-methylglycine amide and N-acetyl-N′-methyl-alanine amide as functions of the torsional angles (φ,Ψ). The statistical mechanical averages of mK, μ, and γ2 were calculated from conformational energies obtained by the methods of Scheraga.

Notes: The physical properties of single, 5-8-μm diameter, water-swollen elastin fibers have been investigated on a microtest apparatus attached to a polarizing microscope. Analysis of the mechanical and optical properties at extensions below 100% indicate that the elastic modulus (G) has a value of 4.1 × 105 N m-2, the average molecular weight of chains between crosslinks is in the range of 6000-7100, and the stress optical coefficient (C′) is 1 × 10-9 m2 N-1 at 24°C. Analysis of the temperature dependence of the stress optical coefficient indicates that the polarizability of the random link decreases with increasing temperature, with an apparent activation energy for this process of the order of 1.6 kcal/mol. Analysis of the non-Gaussian mechanical and optical properties at extensions above about 100% suggest that the chains between crosslinks contain approximately 10 “effective” random links, with each link consisting of 7-8 amino acid residues. These parameters for the random chains in the elastin network have been used to predict the dimensions of other random proteins. The close correlation of these predictions with published values for the dimensions of a series of proteins in solution in 6M guanidinium hydrochloride provides an independent test of the appropriateness of our analysis.

Notes: Heavy meromyosin binding to F-actin saturated with tropomyosin is studied theoretically. The problem is formulated as a special case of n-mer adsorption to a one-dimensional Ising lattice which is divided into m-site-long blocks.

Notes: A Monte Carlo analysis is presented which establishes a relationship between the rotational diffusion coefficients and the flexibility (persistence length, P) of short, wormlike chains. The results of this analysis are presented in terms of experimentally observable quantities; namely, the rotational relaxation times for the field-free decay of optical anisotropy. The pertinent theoretical quantity is R, defined as the ratio of the longest rotational relaxation time of a wormlike chain to the transverse rotational relaxation time of a rigid cylinder having the same axial length (L) and segmental volume. R, so defined, is essentially independent of the axial ratio of the cylinder for any value of L/P within the range of validity of the present analysis (axial ratio 〉 20; 0.1 〈 L/P 〈 5). It is pointed out that P can be determined with reasonable accuracy even in the absence of a precise knowledge of the local hydrodynamic radius of the chain.

Notes: Solvents which accelerate DNA renaturation rates have been investigated. Addition of NaCl or LiCl to DNA in 2.4M Et4NCl initially increases renaturation rates at 45°C and then leads to a loss of second-order behavior. The greatest accelerations are seen with LiCl and dilute DNA. Volume exclusion by dextran sulfate is the most effective method of accelerating DNA renaturation with concentrated DNA. Addition of dextran sulfate beyond 10-12% in 2.4M Et4NCl fails to increase the acceleration beyond approximately 10-fold. Accelerations of 100-fold may be achieved with 35-40% dextran sulfate in 1M NaCl at 70°C. No other mixed solvent system was found to be more effective, although acceleration may be achieved in solvents containing formamide or other denaturants. The acceleration in 2M NaCl occurs without loss of the normal concentration and temperature dependence of DNA renaturation and is also independent of dextran sulfate concentration if sufficient dextran sulfate is used. Dextran sulfate may be selectively precipitated by use of 1M CsCl.

Notes: In the preceding article, a Monte Carlo analysis was presented which provides a quantitative numerical relationship between the rotational diffusion coefficients, as measured by the decay of optical anisotropy following an electric field pulse, and the flexibility (persistence length) of short, wormlike chains. In the present article, the results of the foregoing analysis are applied to the observed rates of decay of birefringence for a series of sequenced DNA fragments ranging in size from 104 to 910 base pairs. Under the conditions used in this study, the DNA fragments exist as native, duplex molecules. Furthermore, conditions are defined in which the observed relaxation times are not dependent on DNA concentration, field strength, or the duration of the pulse. It is pointed out that the ionic atmosphere associated with a wormlike polyion does not exert any significant (direct) influence on the rotational diffusion of the polyion and, therefore, that the rotational relaxation times are a true measure of the configurations of the DNA molecules in solution. Moreover, excluded-volume effects are shown not to be significant for the moderately short molecules employed in this study. The major conclusion of this study is that there is no strong ionic strength dependence of the persistence length for ionic strengths above 1 mM and that the persistence length, under conditions where electrostatic contributions are negligible, is approximately 500 Å. For ionic strengths significantly lower than 1 mM, electrostatic contributions to the stiffness of DNA become significant.

Notes: The aqueous and hydroalcoholic solutions of the heptenic macrolide amphotericin B display strong and variable signals in CD and absorption spectroscopies in the range of the π* ← π transition. An interpretation of the spectroscopic changes is proposed based on the equilibrium between two forms of the intermolecular organization: the aggregated one (A) with strong excitonic interaction and the nonaggregative one (B) whose spectra are like those of linear conjugated polyenes in true solution with a well-developed vibrational structure. The intermediate spectra are fitted by linear combination of the A- and B-form spectra. A two-level organization of the aggregates is proposed for the A-form: (1) a close packing of few molecules, which is the origin of the absorption maxima hypsochromic shift; and (2) interaction between the preceding small units inside the aggregates, which is spectroscopically expressed by the intense CD couplet.

Notes: Polypeptides of dicarboxylic amino acids having the monomer units linked in α- and ω-peptide bonds contain two kinds of carboxyls of different acidity. How well potentiometric titration can distinguish these two carboxyls and so characterize the nature of the peptide bonds is evaluated critically. An analysis of the equation describing the dependence of pH on the degree of neutralization based on neglecting the polymer effect and a discussion of the dissociation behavior of polyanions show that the method of evaluating experimental data found in the literature is incorrect. Nevertheless, if a conformational transition does not interfere, some useful and reliable information may be gained by this method; namely, an indication of the presence of two different peptide bonds, their mole ratio, and an approximate pK value for the carboxyl of the amino acid linked in the ω-peptide bond. The presence of two types of carboxyls complicates the evaluation of the titration curves in the conformation studies.

Notes: Conformational analysis of antiparallel double-helical polynucleotides with Watson-Crick base pairing was reduced to a four-dimensional problem using original mathematical methods. In the four-dimensional conformational space the family of structures, characterized by the base-pair stacking with the most stable conformations in water solution as well as in the solid state, was localized. For the C′2-endo sugar pucker, both right-handed and left-handed structures were found; right-handed structures only, however, seem to be allowed for the C′3-endo pucker, the only possible one for ribonucleotides with base stacking.

Notes: Angiotensin II and its competitive inhibitor [Sar1, Ile8]-angiotensin II, as well as several analogs of these two compounds specifically chosen for their well-defined pharmacological properties, were studied by circular dichroism and nuclear magnetic resonance methods at various pH values in aqueous solution and in d6-dimethylsulfoxide. The results were compared with their biological activities. This allowed us to establish relationships between conformation and pressor activity, explaining most of the properties of angiotensin II, its inhibitor, and the analogs successively substituted in positions 3 and 5.

Notes: Peptide agonists covalently attached to tobacco mosaic virus exhibit such unusual properties as superpotency, superaffinity, enhanced resistance towards enzymic degradation, and prolonged action at the target cell. These properties can be exploited for the isolation by density-gradient centrifugation of membrane vesicles bearing specific receptors for the peptides and for radioactive and fluorescent labeling of cell-surface receptors. Our observations can be explained by cooperative-affinity phenomena caused by the deployment in space of the agonist molecules.

Notes: The early steps of fibrin aggregation induced by low Reptilase concentrations were studied by means of static and dynamic light scattering. In order to obtain information on the size and shape of the first oligomers, the angular dependence of the scattered intensity and the mean Rayleigh line width were measured. Under physiological pH and ionic strength, oligomer formation was detectable immediately after enzymatic activation. Comparison of the calculated data for different models with experimental results shows that the early fibrin polymerization proceeds as an end-to-end aggregation of elongated and possibly flexible molecules approximately 75 nm long.

Notes: The equivalent conductivity of salt-free solutions of deoxyribonucleates of alkali metals and ammonium obtained by filtering an isoionic DNA solution through a cation exchanger in the corresponding form has been investigated in the concentrations range of 1 × 10-4 to 4 × 10-3M. For all counterions investigated there is a linear dependence of the equivalent conductivity on \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {C_p} $\end{document}, where Cp is the nucleic phosphorus concentration. The limiting equivalent conductivity of deoxyribonucleates increases linearly with the limiting mobility of a counterion. By extrapolation to the zero mobility of the counterion, we have obtained the limiting mobility of a macroion, which is equal to 19 × 10-4 Sm m2 equiv.-1, which is in good agreement with the literature data for denatured DNA obtained by the method of a moving boundary. It is shown that the degree of binding of counterions calculated from the conductometric data in diluted DTA solutions in independent of the nature of the univalent counterion. The degree of dissociation of H+-DNA in the isoionic solution calculated with allowance for the fraction of unprotonated bases practically coincides with this value for salts of DNA. The parameter of Manning's theory calculated from the experimental data corresponds to the distance between phosphates along the chain of the macroion, which is equal to 6.7 Å. We attribute the smaller value of this distance as compared with the theoretical one for denatured DNA to the aggregation of macroions.

Notes: A hydrate of cellulose II can be formed by swelling Fortisan fibers in hydrazine and then washing in water. The hydrate is stable at 93% relative humidity and has a monoclinic unit cell with dimensions a = 9.02 Å, b = 9.63 Å, c = 10.34 Å, and γ = 116.0°; the space group is P21. The unit cell contains disaccharide sections of two chains and approximately four water molecules. The structure was refined using the LALS method, based on 10 observed and 10 unobserved reflections. An antiparallel arrangement of adjacent chains was assumed, since this occurs in cellulose II (the starting material), and the hydrate also reverts to cellulose II on dehydration. Refinement of the positions and side-chain conformations of the chains shows that the chains are stacked in the same way as in cellulose II, and the hydrate is formed by insertion of water molecules between the stacks. However, all efforts to arrange the water molecules in crystallographically regular positions led to unsatisfactory agreement between the observed and calculated intensities. These results suggest an irregular arrangement of the water molecules, which was modeled using water-weighted atomic scattering factors. The analysis resulted in two refined models with relative chain staggers of ∼ +c/4 and ∼ -c/4, which are indistinguishable in terms of the x-ray agreement. Our preference is for the +c/4 model, for which the stacks of chains are analogous to those in cellulose II.

Notes: The interaction of calcium ions with α-elastin has been investigated by equilibrium dialysis, CD, and microcalorimetric techniques. Consistent with literature data, it was found that the interaction in water is very poor. In trifluoroethanol (TFE), equilibrium dialysis experiments showed that calcium ions bind to ∼-elastin with an association constant of ∼250 L × mol-1. Such a figure is not consistent with highly specific, highly selective binding. It was also found that the CD response is not directly proportional to the amount of bound calcium but depends on the protein concentration. From microcalorimetric experiments it was found that the heat effect relative to the binding process is of the order of 1.9 kcal/g ion. From this figure and from the binding constant, a positive ΔS value of about 17 e.u. was evaluated, leading to the conclusion that the binding process is entropy driven. From microcalorimetric measurements a ΔH of 1.5 kcal/residue was found for the calcium-induced conformational transition of the protein.

Notes: Die Rheinanliegerstaaten haben im gemeinsamen Bemühen um die Qualität des Rheinwassers schon 1963 die „Internationale Kommission zum Schutze des Rheins gegen Verunreinigung“ (IKSR) ins Leben gerufen. Die IKSR überwacht die Wasserqualität und gibt einen jährlichen Bericht mit Analysendaten heraus. Außerdem erarbeitet sie Vorschläge für Maßnahmen zum Schutze des Stroms. In Ergänzung der jeweiligen nationalen Gewässerschutzmaßnahmen haben die Rheinanliegerstaaten 1976 das Übereinkommen zum Schutze des Rheins gegen chemische Verunreinigung (Chemieabkommen) abgeschlossen. Das Chemieakbkommen, durch das die Ableitung bestimmter gefährlicher Stoffe aus den Stoffgruppen und -familien: Queck-silber- und Cadmiumverbindungen, organische Halogen-, Phosphor- und Zinnverbin-dungen, cancerogene Stoffe so weit wie möglich verhindert und aus weiteren Stoffgruppen und -familien, darunter den meisten Metallen, streng überwacht und eingeschränkt werden soll, hat einen langfristigen präventiven Charakter. Das Chloridabkommen soll dagegen sofort zu Maßnahmen führen. Zu diesen Abkommen der Rheinanliegerstaaten treten eine Reihe weiterer internationaler Abkommen und Vereinbarungen mit Auswirkungen auf den Rhein, verschiedene Richtlinien der Europäischen Gemeinschaft, ein geplantes Abkommen der Länder im Europarat, ein Abkommen zum Schutze der Nordsee und des Nordatlantiks gegen die Verschmutzung vom Lande aus.

Notes: We have measured the ultraviolet CD spectra for covalently closed and linear forms of phage PM2 DNA in solution. We find that increased concentrations of salt or ethanol (up to 50% ethanol by weight) depress the long-wavelength positive CD bands in the spectra of both forms of DNA, although the spectrum of the native covalently closed DNA always has a slightly larger magnitude of these bands than does the spectrum of the linear DNA. In addition, both DNAs are equally capable of undergoing a transition to the A conformation in 70-80% ethanol at low Na+ concentrations. Thus, the constraint imposed by the covalent closure of a DNA molecule does not seem to hinder its conformational response to these changing solution conditions. Lang [(1973) J. Mol. Biol. 78, 247-254] has found by electron microscopy that T7 DNA has an inherent ability to condense into compact particles, suggested to be supercoils of multiple order. Both covalently closed and linear forms of PM2 DNA also become condensed when the DNA, in 0.2M ammonium acetate and 1 mM EDTA, is exposed to ethanol and subsequent drying on specimen grids [Lang, D., Taylor, T. N., Dobyan, D. C. & Gray, D. M. (1976) J. Mol. Biol. 106, 97-107]. Under similar conditions, in solutions of 0.2M ammonium acetate and 1 mM EDTA to which ethanol is added, we have measured the CD spectra of both covalently closed and linear forms of DNA. Below ethanol concentrations at which the DNA obviously precipitates, the CD spectra of both forms have reduced long-wavelength positive CD bands.

Notes: The polymeric cobalt(II) porphyrin complexes were prepared from cobalt(II) protoporphyrin IX dimethyl ester(Co(II)P) and copolymers of 4-vinylpyridine and styrene(PSP), and their binding ability of molecular oxygen was studied in toluene solution. The five- and six-coordinate structure of CoP-PSP complexes were confirmed by esr spectra. The esr parameters for the CoP-PSP complexes were not affected by the molecular weight and the vinylpyridine-unit content of PSP-ligand. The 1:1 dioxygen-Co complex was reversibly formed when the solution of CoP-PSP was exposed to oxygen atmosphere at low temperature. While the visible spectra and esr parameters for the dioxygen complexes of CoP-PSP were the same as those of the CoP-pyridine complex, the equilibrium constant for the oxygen binding increased with the vinylpyridine-unit content of the PSP-ligand. The larger entropy change was observed for the oxygenation in the CoP-PSP system especially, of which the vinylpyridine-unit content was large.

Notes: The low-temperature dynamic mechanical relaxation of ox Ligamentum nuchae elastin, swollen with water and ethylene glycol at various swelling ratios, has been investigated by means of the Rheovibron DDV II viscoelastometer, at frequencies from 3.5 to 110 Hz. The peak location on the temperature scale, its intensity and activation energy have been studied as a function of solvent content and it has been found that the two solvents influence the dynamic mechanical behavior in a quite different way. A similar interaction of the solvent molecules with the backbone peptide groups is assumed for both solvents, and the differences in the mechanical spectra, which are more marked the higher the solvation degree, are explained in terms of the different size of the protein-solvent relaxing units.

Notes: The relation between the chemical structure of a protein and the physical properties of a heat-set gel of that protein has been investigated. The physical properties of the gel are determined by means of mechanical experiments in which the viscoelastic properties of the gel are determined in terms of the storage shear modulus, the loss modulus and the stress-strain curve. The storage shear modulus defined the solid (elastic) character of the gel. The chemical structure of the protein and the nature of the solvent determine the nature and number of cross-links in the gel. The cross-links in gels formed by heating concentrated solutions of ovalbumin in 6M urea solutions were found to be disulfide bridges and the mechanical properties of these ovalbumin/urea gels approximated those of an ideal rubber. The latter finding enables one to calculate the number of cross-links per ovalbumin molecule from the value of the storage modulus, using the classical theory of rubber elasticity. This theory, together with the Flory-Huggins lattice model, can also be used to calculate the number of cros-links per ovalbumin molecule from the swelling behavior of ovalbumin/urea gels. The number of cross-links per ovalbumin molecule calculated from these two types of experiments are in mutual agreement and correspond with the number of thiol groups in ovalbumin. We conclude, thereforee, that theories of polymer physics can be used to relate the chemical structure of a protein to the physical properties of its gel.

Notes: The single-strand helix-coil transition in various oligo- and polyadenylates is characterized by means of an improved cable temperature-jump technique. In all the polymers studied {poly(rA), poly(dA), poly[A(m2′)] and poly[A(e2′)]} helix-coil relaxation is observed in the time range from 30 to 1000 nsec. Relaxation-time constants observed at wavelengths λ〈280 nm (τα) are different from those found at λ 〉280 nm (τβ), indicating the presence of more than two conformational states. The time constants τα increase in the series poly(dA), poly[A(m2′)], constants τβ/τα is approximately 2.5, except in poly(dA) where τβ/τα ≈ 9. Relaxation measurements with r(A)n- oligomers show a decrease in conformational mobility with increasing chain length. The relaxation curves also demonstrate that “internal” residues have lower reaction rates than residues at the ends of the oligomer chain. Measurement in D2O reveal a solvent isotope effect for τα of +87% for poly(rA), and of +53% for poly(dA), whereas no isotope effect is found in τβ. The absence of “slow” relaxation processes in the model compound 9,9′ -trimethylenebisadenine shows that the relatively low rate of the single-strand helix-coil transitions is due to the coupling of base stacking with the folding of the sugar-phosphate chain. The absence of a seprate relaxation process (corresponding to τβ) in 9,9′-trimethylenebisadenine, as well as in the dinucleotides ApC and CpA, suggests that this relaxation process is dependent upon the presence of both the sugar-phosphate chain and of adjacent adenine bases. The experimental data provide evidence that there is more than one ordered conformation in various single-stranded oligo- and polyadenylates and that the transition between these conformations is influenced by the sugar conformation.

Notes: An algorithm has been developed that permits one to find all possible conformations of the sugar-phosphate backbone for any given disposition of DNA base pairs. For each of the conformations thus obtained, the energy of the helix was calculated by the method of atom-atom potentials. Several isolated regions in the space of the bases′ parameters (Arnott's parameters) have been found for energetically favorable helical structures. Two parameters, the distance of a base pair from the helix axis, D, and the windling angle, τ, allow one to subdivide possible conformations into the families of closely related forms. Two regions (ravines) on the (D, τ) map correspond to the know A and B families. In the B family a continuous transition has been obtained in which the double helix undergoes increasing winding, while the base pairs are moving toward the major (nonglycosidic) groove.Interrelationships between the variables, characterizing the spatial structure of the double helix, D, τ, TL and χ, when going along the bottom of the B ravine, were also obtained.Besides the Known A and B families, several new ones were found to be energetically possible. Among these the strongly underwound helices with the negative D values, as well as the forms with the C4-C5 angle in a trans position, should be mentioned.Biological roles of the different double-stranded conformations, in particular, in protein-nuclei acid interaction are discussed.

Notes: The theoretical basis for the statistical mechanical deconvolution of a thermally induced macromolecular melting profile is presented. It is demonstrated that all the thermodynamic quantities characterizing a multistate macromolecular transition can be obtained from the average excess enthalpy function, 〈ΔH〉, of the system, without any assumption of the particular model or mechanism of the reaction.Experimentally, 〈ΔH〉 is obtained from scanning calorimetric data by direct integration of the excess apparent molar heat capacity function, ΦCp. Once 〈ΔH〉 is known as a continuous function of the temperature, the partition function, Q, of the system can be calculated by means of the equation \documentclass{article}\pagestyle{empty}\begin{document}$$Q_{\left( T \right)} = \exp \smallint _{T_0}^T {\left( {\frac{{\left\langle {\Delta H} \right\rangle }} {{RT^2}}} \right)} dT $$\end{document} From the partition function all the thermodynamic quantities of the system can be obtained. It is shown that the number of discrete macroscopic energy states, the enthalpy and entropy changes between them, and the relative population of each state as a function of temperature can be calculated in a recursive form.

Notes: The high-resolution 1H-nmr study of the ferrichrome cyclohexapeptides, in d6-DMSO solutions, has been extended to the amide NH spectral region. A total of ten diamagnetic analogues of ferrichrome that differ in the coordinated metal ion (Al3+, Ga3+ or Co3+), the primary structure, the nature of the bidentate hydroxamate moiety, or the isotope compositions (14N, 15N) have been investigated. The 3JαNH values reflect regiorous conformational isomorphism throughout the complete suite of analogues, quite independent of the residue occupancy of each site. Totally resolved amide multiplets have been obtained in most cases and the four-line (doublet of doublets) appearances of glycyl NH resonances has been observed for the first times; these data enabled stereospecific assignment and accurate analysis of the NH-CαH proton spin systems. The high resolution was made possible by the use of a suitable spectral deconvolution shceme at 360 MHz. The fine structure, extraordinarily well displayed in the 15N-peptide spectra, provides a series of parameter values whose consistency has been checked by computer simulation. Since the crystallographic structure for two of the ferric peptides is known to 0.002-Å resolution, a 3J vs θ correspondence could be confidently established. A Karplus curve was derived from the combined x-ray and nmr data: \documentclass{article}\pagestyle{empty}\begin{document}$$ ^3 J_{\alpha {\rm NH}} = 5.4\cos ^2 \theta - 1.3\cos \theta + 2.2{\rm Hz} $$\end{document} It is suggested that seriously nonplanar amides can exhibit 3JαNH values higher than predicted by the ferrichrome curve.

Notes: The general formulas describing the low-angular dependence of polarized (Vv) and depolarized (Hv) light-scattering intensity by a chain macromolecule of arbitrary form with anisotropic polarizability are derived. It is shown that the value dHv/dtHvo (where t = [〈R2〉S/L]2, S being the scattering vector) is an indication of the chain-flexibility mechanism. This permits one to distinguish between the models of a wormlike chain, regular zigzag, or statistical zigzag. The results of numerical calculations useful for the interpretation of experimental data are presented.

Notes: The kinetics of the fluorescence decay of the energy donor in a homologous series of oligopeptides each containing at its ends a donor and an acceptor of electronic excitation energy was investigated in solvent mixtures of different viscosities. The repeating unit in the peptides was N5-(2-hydroxyethyl)-L-glutamine and the chromophores used as donor and acceptor were naphthalene and dansyl, respectively. The number of units in the peptides studied varied from four to nine. The solvents used were mixtures of glycerol and trifluoroethanol in various proportions. The decay rate of the donor fluorescence increases when the solvent viscosity decreases. This behavior is due to the disturbance of the equilibrium end-to-end distribution of distance of the excited molecules by the energy transfer process, which is more favorable foe short than for long distances. The subsequent rearrangement towards the equilibrium distribution by diffusion of the molecular ends relative to one another enhances the efficiency of the energy transfer. Assuming a modified Fick equation to describe this diffusion motion, the fluorescence decay data were analyzed in terms of a diffusion coefficient describing the Brownian motion of the molecular ends. The diffusion coefficients thus evaluated increase systematically upon decreasing the solvent viscosity. For example, for the oligopeptides studied it changes from unmeasurably small values in glycerol solution to values varying between 10-8 to 10-7 cm2/sec at room temperature in a glycerol trifluoroethanol solvent mixture of viscosity of 8 centipoise. The values obtained for the diffusion coefficient are smaller by about an order of magnitude than the values expected for the diffusion coefficients of the free chromophores in solvents of comparable viscosity. It is thus concluded that the backbone of the polymeric chains possesses appreciable internal friction which exerts resistance to the Brownian motion of the polymer chains. The diffusion coefficient of the end-to-end motion is systematically smaller for the shorter than for the longer chains. For example, at room temperature in a solvent mixture of 8 centipoise it is 3×10-8, 5×10-8, 7.6×10-8, and 8.5×10-8 cm2/sec for oligomers containing four, five, eight, and nine N5-(2-hydroxylethyl)-L-glutamine repeating units, respectively. The internal friction thus impedes the motion of the molecular ends more effectively in the shorter chains than in the longer ones.Analysis of the energy-transfer experiments in solvents spanning a wide range of viscosities shows that the orientational factor appearing in Förster's equation for energy transfer does not interfere perceptibly with the evaluation of the end-to-end distances from the fluorescence decay data when naphthalene and dansyl serve as donor and acceptor, respectively. This is due to the fact that both the donor emission and acceptor absorption in the range of spectral overlap are characterized by more than one transition dipole moment, as is evident from the corresponding polarization data.

Notes: Raman spectroscopic studies have been carried out on polymers of L-valine ranging in degree of polymerization (DP) from 2 to 930. The spectrum of the hexapeptide (DP = 6) is closely similar over the entire range 40-1750 cm-1 to those of polymers with much higher DP, and the structure is clearly shown to be that of the antiparallel pleated sheet (β-structure) by the amide I and III frequencies. The formation of a little α-helical structure occurs in polymers with DP above 500, although the amount does not appear to be a linear function of DP. The α-helical structure is unstable and readily destroyed in samples cast from trifluoroacetic acid solution. It is stabilized by the incorporation of L-alanine, a strong helix-former; polymers of the latter may in turn be forced into a α-structure in copolymers sufficiently rich in L-valine.

Notes: The fluorescence properties of several cooligopeptides of glycine, phenylalanine, and tryptophan, containing one or two aromatic residues, are investigated. In particular, a detailed analysis is made of the influence of pH upon the quantum yield and the position of the emission maximum (λmax) in H-Trp-Trp-OH, H-Trp-Gly-OH, H-Gly-Trp-OH, H-Gly-Trp-Gly-OH, H-Trp-Trp-OH, H-Trp-Trp-Gly-OH, H-Gly-Trp-Trp-OH, H-Phe-Trp-OH, H-Phe-Trp-Gly-OH, H-Gly-Phe-Trp-OH, and H-Gly-X-(Gly)n-Trp-Gly-OH, with X = Phe or Trp, and n = 0,1,2. It is shown that raising the pH from ca. 2 to 11 results in a red shift of λmax, and an increase in the quantum yield. These changes, mostly structure dependent, are in most cases attributable to electronic perturbations acting directly upon the λmax of the fluorophore(s) and upon the quenching efficiency of the free amino and carbonyl groups. For the compounds having two adjacent tryptophyl residues, it is shown that the two fluorophores do not appear to have the same emission properties and the quantum yield is lower than expected. The causes of this behavior are discussed in terms of conformational effects, stacking interactions, and radiationless energy transfer. Finally, an attempt is made to correlate fluorescence data with previous circular dichroism data which had indicated the occurrence of a conformationally rigid structure for some of the compounds having two adjacent aromatic residues.

Notes: Group-specific polysaccharides isolated by means of a cetavlon procedure are immunogenic in man and induce protective immunity against meningococcal meningitis. Minute quantities of the polymers in solution can act as vaccines. We now report the first characterization of a fractionated (C-1) group C polysaccharide in 0.4KM KCl and 0.05M sodium acetate by means of light-scattering spectroscopy. Independent measurements of refractive index increments, absolute scattered intensities, angular scattering intensities and line widths as a function of scattering angles and delay times at different concentrations using incident wavelengths of 632.8 nm from a He-Ne laser and of 488 nm from an argon-ion laser yield information on aggregation properties, molecular weight (Mr), radius of gyration 〈r0g〉1/2z, translational diffusion coefficient 〈D〉0z, and second virial coefficients A2 and B2 of C-1 polysaccharide.At relatively high ionic strength (0.04M KCl + 0.05M sodium acetate), we obtain for the C-1 polysaccharide in solution Mr = 5.15 × 105, 〈r2g〉1/2z = 345 Å, A2 = 1.25 × 10-4 ml/g, 〈D〉0z = 1.16 × 10-7 cm2/sec with a corresponding Stokes radius of 240 Å and B2 = 4.4 ml/g. A2 and B2 are the second virial coefficients from intensity- and diffusion-coefficient measurements. The C-1 polysaccharide aggregates in solution and behaves hydrodynamically like random coils. Viscosity and sedimentation studies further confirm our conclusions that the fractioned C-1 polysaccharide aggregates in solution and EDTA can partially break up those aggregates. However, the system remains polydisperse even after adding an excess amount of EDTA. The weight-average molecular weight of the C-1 polysaccharide in solution depends upon ionic strength and exhibits a minimum at ∼0.2M KCl. Finally, viscosity, light-scattering, and sedimentation results all show that the aggregated macromolecular system behaves like random-coiled polymers with no measurable shape factors.

Notes: We extend fluorescence correlation spectroscopy to systems that undergo translation or laminar flow in a sample cell. We include theoretical and experimental results; we consider uniform and nonuniform velocity profiles. Concentration correlation analysis extracts microscopic rate parameters from measurements of the spontaneous concentration fluctutations, which occur even at equilibrium. Fluorescence is one of the most sensitive means of monitoring these fluctuations. Analysis of flowing or translating systems (1) offers a method of measuring number concentrations of selected species, for example, of aggregates or polymers, (2) provides a nonperturbing velocity probe, (3) sometimes allows one to circumvent photolytic degradation, (4) has proved extremely helpful in testing and aliging apparatus for fluorescence correaltion measurement and in verifying theoretical analyses, and (5) may be required for interpretation of results obtained on systems in motion, even though that motion is undesired or initially unsuspected. We include both theoretical and experimental results for combined Poiseuille flow and diffusion in the geometry which is of most practical interest. Theoretical expressions for the much simpler cases of nondiffusive Poiseuille flow as well as uniform flow or translation with or without diffusion constitute limiting cases which are displayed explicitly.

Notes: In the preceding article1 we demonstrated that the partition function of a system is experimentally accessible from scanning calorimetric data. In this article the general results of the deconvolution theory are applied to the general case of cooperative transitions in macromolecules. It is demonstrated that, in the limit of very large systems, all the relevant molecular averages and molecular distribution functions can be directly obtained from the experiment. In doing this, the method of the grand partition function is used. It is shown that in the case of homopolymers, only one parameter, the stability constant, needs to be explicitly specified for a complete description of the system. Since the partition function is directly evaluated from the experiment, no special assumptions or artificial constraints directed to obtain a mathematically solvable model are required. This result offers the unique opportunity of having direct experimental access to statistical averages of systems in which the partition function cannot analytically be solved. Consequently, the theory can be extended to cooperative transitions occurring in two and three dimensions by introducing cluster distribution functions.

Notes: The pyridoxal Schiff bases of the polypeptides poly(L-lysine), poly(L-ornithine), and poly(L-α,γ-diaminobutyric acid) were prepared and investigated in water/methanol by CD spectra and equilibrium dialysis experiments. Only the poly(L-α,γ-diaminobutyric acid) derivative is characterized by a relevant optical activity similar to that found in pyridoxal enzymes. The stereospecific interactions between the pyridoxylideneimine group and the polypeptide chain prevent the hydrolysis reaction of the aldimine bond.

Notes: The protein turkey-heart cytochrome c is used as a model protein to study charge effects in sedimentation equilibrium experiments in three-component solutions. Data are given for the dependence of the apparent M (1-υρ) on ρ in solutions of KCl, RbCl, CsCl, and triethylamine hydrochloride. The results show the Donnan effect to have a significant influence on the apparent molecular weight, found by extrapolation of the data to a solution density of one. The apparent molecular weights are for protein at infinite dilution. A theoretical treatment is presented where the magnitude of this effect can be predicted accurately from the formal net charge of the protein as computed from the amino acid composition. The results are shown to be important in computing the preferential hydration of the protein in concentrated salt solutions. For such systems the Donnan effect should be subtracted from the total interaction coefficient for multicomponent system in order to obtain the preferential hydration.

Notes: The cupric complexes of poly(Nε-acetoacetyl-L-lysine), [Lys(Acac)]n′ poly(Nδ-acetoacetyl-L-ornithine), [Orn(Acac)]n′ and poly(Nγ-acetoacetyl-L-diaminobutyric acid), [A2bu-(Acac)]n, as well as of the model compound n-hexyl acetoacetamide, have been investigated by means of absorption, potentiometric, equilibrium dialysis, and CD measurements. While in the complex of the model compound, one chelating group is bound to one cupric ion, in the polymeric complexes two β-ketoamide groups are bound to Cu(II) under the same experimental conditions. The binding constant of cupric ions to the three polymers and the formation constant of the Cu(II)-nhexylacetoacetamide complex have been evluated. Investigation on the chiroptical properties of the three polymeric complexes shows that the peptide backbone does not undergo conformational transitions, remaining α-helical when up to 20% of the side chains are bound to Cu(II). The optical activity of the β-ketoamide chromophores is substantially affected by complex formation and is discussed in terms of asymmetric induction from the chiral backbone.

Notes: The Mettler/Paar precision density meter DMA-02D has been used to determine the concentration of saturated solutions of amino acids at 20.0, 25.0, and 29.8 °C. The technique has proven itself an elegant and precise method. The solubilities of all of the amino acids with the exceptions of proline, lysine, and cystine have been measured. The Gibbs free energies of transfer from saturated water solution to 1M Na2SO4 and to 1M Gu·HCL along with the van't Hoff heats and entropies have been calculated. The van't Hoff heats have been compared with the calorimetrically determined heats for some of the amino acids. The Lumry-Rajender relation between the entropy and heats has been observed. The process of transfer of the amino acids from water to the solvents is primarily enthalpic rather than entropic.

Notes: The effect of magnesium ions on the parameters of the DNA helix-coil transition has been studied for the concentration range 10-6-10-1M at the ionic strengths of 10-3M Na+. Special attention has been given to the region of low ion concentrations and to the effect of polyvalent metallic impurities present in DNA. It has been shown that binding with Mg++ increases the DNA stability, the effect being observed mainly in the concentration range 10-6-10-4M. At[Mg++]〉10-2M the thermal stability of DNA starts to decrease. The melting range extends to concentrations ∼10-5M and then decreases to 7-8°C at the ion content of 10-3M. Asymmetry of the melting curves is observed at low ionic strengths ([Na+] = 10-3M) and [Mg++] ≤ 10-5M. The results, analyzed in terms of the statistical thermodynamic theory of double-stranded homopolymers melting in the presence of ligands, suggest that the effects observed might be due to the ion redistribution from denatured to native DNA. An experimental DNA-Mg++ phase diagram has been obtained which is in good agreement with the theory. It has been shown that thermal denaturation of the system may be an efficient method for determining the ion-binding constants for both native and denatured DNA.

Notes: Studies on the cross-linking of a tripeptide (t-butyloxycarbonyl-L-alanyl-D,L-2-amino-6-heptenoyl-L-alanine methyl ester) have shown that it is possible to form specific cross-links in good yields through Schiff base formation of the ε amino group of lysine. The heptenoic acid residue has been ozonized to an aldehyde and condensed with the ε amino of lysine in the compounds alpha-t-butyloxycarbonyl-L-alanyl-L-lysine methyl ester and alpha-t-butyloxycarbonyl-L-lysine methyl ester to form the cross-link, lysinonorleucine. This compound has been stabilized by reduction with sodium borohydride and quantitated on the amino acid analyzer. This technique converts from 60 to 98% of the available aldehyde to lysinonorleucine.

Notes: The determination of structural changes in antibodies due to their specific interaction with antigenic proteins is an important problem in understanding immunological responses. The method of polarized ATR infrared spectroscopy applied to protein films adsorbed on an appropriate solid surface can give information about the conformation of the polypeptide chains, as well as their orientation with respect to the surface. The adsorption of anti-rabbit serum albumin onto monomolecular films of rabbit serum albumin, bovine serum albumin, and ovalbumin, and of anti-ovalbumin onto films of rabbit serum albumin and ovalbumin at a Ge-aqueous interface have been studied by this technique. The intensity of the amide I absorption indicates that the strengths of binding of these three albumin proteins with anti-rabbit serum albumin is, under appropriate conditions, in the order rabbit 〉 bovine ≫ ovalbumin; with anti-ovalbumin, it is ovalbumin ≫ rabbit. Since the frequencies of the amide I band appear near 1655 cm-1 for all the proteins and protein complexes studied, the major contributions to their conformation comes from α-helix and random-coil structures. The average orientation of the transition moments of the amide I and A bands has been shown to be about 75° with respect to the surface normal. This indicates that the polypeptides chains are on the average approximately parallel to the surface for all the systems studied. Consequently, the effect of the specific antibody-antigen interaction on the conformation and orientation of the former seems negligible in these films.

Notes: The Raman spectra of guanylyl (3′-5′) guanosine (GpG) in solution in H2O and D2O at pH 3-7 have been recorded at various temperatures between 0 and 80°C. The results are consistent with the existence in the lower temperature range of stable aggregates formed by the stacking of GpG tetramers. The aggregates melt cooperatively near 60°C, which results in important changes in the spectra. Among these, a large increase in intensity of some of the bands assigned to the guanine residues shows that unstacking of the bases occurs at the melting. Also apparent in the spectra are changes in the intensity and frequency of band attributable to molecular groups involved in intermolecular hydrogen bonding between adjacent molecules in the complex. The melting temperature of GpG decreases by approximately 15°C upon lowering the concentration from 5 × 10-2 to 5 × 10-4M, as shown by Raman, calorimetric, CD, and uv measurements. The experimentally determined ΔH and ΔS for the melting transition are 9 Kcal/mol and 28 e.u./mol, respectively. The aggregation of GpG in 1.5 × 10-3M solutions was found to be very slow. The half-time of the process, which roughly follows first-order kinetics, is approximately 3 min at 10°C and 21 min at 35°C. The negative energy of activation associated with this reaction (-143 Kcal) indicated that the process involves intermediates whose concentrations decrease the temperatures raised, thus slowing down the overall process. The rate of disaggregation of GpG upon dilution to very low concentration is also extremely slow, indicating that the GpG aggregates, once formed, are very stable.

Notes: The Raman spectra of poly(L-lysine) with various structures, ionized poly(L-glutamic acid), and deuterated N-methylacetamides have been observed using visible and the 257.3-nm laser lines as the light source. Most of the Raman bands with significantly enhanced intensities in the uv-excited spectra of the polymers have been assigned to the vibrations associated with the C=O and C-N stretching modes, the amide I, II, III, I′, II′, and III′, with reference to the results obtained for simple amide molecules including the deuterated N-methylacetamides. Several amide frequencies have been newly identified and the structures of the polymers have been discussed through the comparison of the Raman and ir amide frequencies.

Notes: Real and imaganiry parts of complex dielectric constant of dilute solutions of DNA in 10-3M NaCl with molecular weight ranging from 0.4 × 106 to 4 × 106 were measured at frequencies from 0.2 Hz to 30 kHz. Dielectric increments Δε were obtained from Cole-Cole plots and relaxation times τD from the loss maximum frequency. The τD of all samples agrees well with twice of the maximum viscoelastic relexation time in the Zimm theory, indicating that the low-frequency dielectric relaxiation should be ascribed to be the rotation of DNA. The rms dipole moment, which was obtained from Δε, agree well with that calculated from the counterion fluctuation theory. The dielectric increment was found to be greatly depressed in MgCl2, which is resonably interpreted in terms of a strong binding of Mg++ ions with DNA.

Notes: Ultravoilet photoelectron spectroscopy has been employed to exmamin the valence electronic structure of 5-fluorouracil, 5-chlorouracil, 5-bromouracil, and 5-iodouracil. Photoelectron bands associted with the three highest π orbitals and the two oxygen atom lone-pair orbitals were assigned by a comparison to similar bands observed in the photoelectron spectrum of uraciul. Bands arising from the halogen atom lone-pair orbitals were assigned by comparing the present results with photoelectron spectra measured for halobenzenes, and by considering the linear dependence of halogen atom lone-pair ionization potentials upon halogen atom electronegativities. The present spectroscopic results have been compared with results from studies of association constants of 5-halouracil-adenine complexes. This examination in dicates that the complex association constants incresase as the ionization potentials of the highest occupied π orbital and the halogen atom lone-pair orbitals of th halouracils decrease.

Notes: Electric dichroism measurements on poly(A) in low-ionic-strength solution demonstrate that below a molecular weight of 130,000 the double-stranded polymer is hydrodynamically rigid and above that molecular weight becomes increasingly flexible. At 500,000 it is considerably more flexible than DNA of the same molecular weight, with a mean end-to-end distance of about 1150 Å compared to approximately 1600 Å for DNA. The fully extended length for both DNA and poly(A) of this molecular weight is about 2750 Å. It is further shown that the orientation of these polyelectrolytes in an electric field is consistent with theoretical treatments of the counter-ion distribution and a preliminary model based on the additivity of classical valence charge anisotropy and counter-ion polarization is postulated for the orientation mechanism. Single-stranded pol (A) is shown not only to retain its base stacking in the presence of the electric field but to extend the persistent regions of stacked bases so that it attains a rodlike structure very similar to the one in the double-stranded polymer is found to be less than that expected from consideration of the x-ray structure. An explanation for this result is sought in the electric asymmetry of the helical polymer.

Notes: The effect of hydration on the solid-state conformation and relaxation behavior of the alkaline earth salts of poly (L-glutamic acid) has been examined. The calcium and strontium salts take the β-conformation and the magnesium salt takes the α-form. No hydration-dependent conformational transitions were observed. The amount of bound water, as measured by differential scanning calorimetry, appears to depend on the size of the cation, while conformation has little or no effect. A relative measure of the barrier to side-chain reorientation was obtained from the temperature of the side-chain (β1) relaxation. It was found that the barrier is determined by electrostatic forces and increases with increasing cation surface charge density. Side-chain motion also appears to be more hindered in the β-conformation than in the α-conformation.

Notes: An optimized potential function for base-stacking interaction is constructed. Stacking energies between the complementary pairs of a dimer are calculated as a function of the rotational angle and separation distance. Using several different sets of atomic charges, the electrostatic component in the monopole-monopole approximation (MMA) is compared to the more refined segmented multipole-multipole representation (SMMA); the general features of the stacking minima are found to be correctly reproduced with IEHT or CNDO atomic charges. The electrostatic component is observed to control the location of stacking minima. The MMA, in general, is not a reliable approximation of the SMMA in regions away from minima; however, the MMA is reliable in predicting the location and nature of stacking minima. The attractive part of the Lennard-Jones 6-12 potential is compared to and parameterized against the expression for the second-order interaction terms composed of multipole-bond polarizability for the polarization energy and transition-dipole bond polarizabilities for approximation of the dispersion energy. The repulsive part of the Lennard-Jones potential is compared to a Kitaygorodski-type repulsive function; changing the exponent from its usual value of 12 to 11.7 gives significantly better agreement with the more refined repulsive function. Stacking minima calculated with the optimized potential method are compared with various perturbation-type treatments. The optimized potential method yields results that compare as well with melting data as do any of the more recent and expensive perturbation methods.

Notes: The 1H-nmr spectra (270 MHz) of cyclic di- and tri-L-azatidine-2-carboxylic acid [cy-clo(L-Aze)2 and cyclo(L-Aze)3] were determined in CDCl3 and D2O and computer simulated. The spectral results were compared with those obtained with cyclo (L-Pro)2 and cyclo (L,-Pro)3. In CDCl3 and D2O solution, the four membered ring of cyclo (L-Aze)2 is puckered with the α-proton in a pseudo-axial position, and the φ angle is smaller in absolute value than -60°, as found for cyclo (L-Pro)2,. The puckering of the four-membered ring of cyclo(L,-Aze)3 in CDCl3 has the α-proton in a pseudo-equatorial position and φ angle larger in absolute value than -60°, in agreement with cyclo(L-Pro)3. In D2O, cyclo(L-Aze)3 was found to interconvert rapidly between different conformers. In the azetidine cyclic peptides studied, the range of values found for the φ angles was smaller than in the related proline cyclic peptides, indicating greater rigidity in the four-membered ring.