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  • Chemistry  (5,684)
  • 2020-2024
  • 1975-1979  (5,684)
  • 1945-1949
  • 1977  (5,684)
  • 1
    Electronic Resource
    Electronic Resource
    A sulphated glycopeptide in human supragingival calculus extracts (1977)
    Springer
    Calcified tissue international 23 (1977), S. 13-17 
    Details
    ISSN: 1432-0827
    Keywords: Dental calculus ; Glycopeptide ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A method is described for the isolation and purification of a sulphated glycopeptide from human supragingival calculus. The compound was isolated after using EDTA treatment, 2 M CaCl2 extraction, proteolytic digestion, ethanol precipitation, and finally purified by DEAE cellulose chromatography. It migrated as a single component on cellulose acetate electrophoresis, and chemical and infrared spectral analysis showed the presence of covalently attached sulphate groups. The sulphated glycopeptide was distinguished from being a sulphated glycosaminoglycan.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02012761
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  • 2
    Electronic Resource
    Electronic Resource
    Proteins of the periodontium (1977)
    Springer
    Calcified tissue international 23 (1977), S. 39-44 
    Details
    ISSN: 1432-0827
    Keywords: Dental cementum ; Collagen ; Protein ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Cyanogen bromide (CNBr) peptides were prepared of the insoluble collagen of bovine dental cementum. Following chromatographic separation, the peptides were identified by their amino-acid composition. Type I collagen ([α1(I)]2α2) accounted for more than 90% of the organic matrix, while Type III collagen ([α1(III)]3) was present at a level of approximately 5%. Amino-acid analyses revealed that the CNBr peptides from α1(I) and α2 chains of cementum closely resembled the corresponding peptides from calf skin. The only systematic difference was a higher level of hydroxylation of prolyl and lysyl residues of the cementum peptides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02012764
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  • 3
    Electronic Resource
    Electronic Resource
    Calcium deficiency, pregnancy, and lactation in rats (1977)
    Springer
    Calcified tissue international 23 (1977), S. 87-94 
    Details
    ISSN: 1432-0827
    Keywords: Calcium ; Osteoporosis ; Lactation ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The calcium homeostatic mechanism was challenged in adult female rats by feeding them a calcium-deficient diet containing oxalate, and by subjecting them to pregnancy and lactation. The regimen caused a substantial weight loss, especially in those animals which reared their young well. Severe hypocalcaemia was observed in the lactating rats. Serum-P was slightly elevated. The content of hydroxyproline in serum was considerably elevated, reflecting the degree of calcium deprivation. Serum proteins were least influenced. The calcium depriving regimen reduced the growth of long bones, but did not stop it. The ash content of the bones was considerably reduced, the degree of reduction depended on the degree of calcium deprivation. Ash as percentage of total bone organ was reduced, but not to the same extent as total ash. Analyses of different parts of femur showed that the proximal and distal parts had lost more bone mineral than the diaphyseal shaft. The ash content of cortical bone tissue from the femur was estimated by a volumetric method. No differences were observed between test groups and controls, indicating that no measurable amounts of bone mineral had been removed from the walls of the vascular canals or by osteocytic osteolysis. Planimetric determinations on cross sections from femora disclosed that a great amount of bone had been removed from the endosteal surface of the diaphysis, while the periosteal surface demonstrated reduced bone apposition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02012771
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of fluctuations in electron density on the excess small-angle X-ray scattering from dilute solutions of macromolecules (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 67-80 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence on the excess scattering function P(μ) of flutuations in the electron density ρ within a macromolecule is treated, to the approximation that the solvent is a structureless medium of constant electron density ρ0. The results for P(μ) and the apparent value of the mean square radius Rapp2, can be expressed as functions of the excess electron density Δρ: P(μ) = X(μ) + (Δρ)-1Y(μ) + (Δρ)-2Z(μ) and Rapp2 = Rx2 + (Δρ)-1Ry2 + (Δρ)-2Rz2, where X(μ) and Rx2 depend only on the shape of the macromolecule, while Y(μ) and Ry2 as well as Z(μ) and Rz2 depend on the shape and the fluctuations in ρ. By varying the electron density of the solvent, the contributions of the shape and the internal structure of the macromolecule can be resolved. The quantities Rx2, Ry2, and Rz2 are evaluated for seven models to illustrate the relative importance of these contributions for representative structures.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160106
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  • 5
    Electronic Resource
    Electronic Resource
    The optical properties of tyrosine-containing cyclic dipeptides (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 121-142 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiroptical properties of the cyclic dipeptides cyclo (L-alanyl-L-tyrosine) and cyclo(L-tyrosyl-L-tyrosine) have been investigated as a function of molecular conformation. Theoretical optical calculations and conformational energy calculations have been carried out as a function of the side-chain dihedral angles χ1 and χ2, and as a function of the angle of fold of the cyclic dipeptide backbone. The results of these theoretical calculations have been compared with experimental circular dichroism (CD) data. Theoretical predictions are in very good agreement with experiment for c(L-Tyr-L-Tyr). Agreement was not quite as good for c(L-Ala-L-Tyr), although the signs of all of the Cotton effects were apparently predicted correctly except for that associated with the lowest energy tyrosine absorption band.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160110
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetic analysis of the annealing period in the formation of the poly(A)·2poly(U) triple helix (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 289-298 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The slow kinetics of annealing processes in multistranded nucleic acids is spectrophotometrically investigated using poly(A)·2poly(U) as a model system. The absorbance changes at specific wavelengths show that double-helical (A·U) base pairs appear as transient intermediates. The annealing process is identified by the enlargement of triple-helical sequences at the cost of (A·U) base pairs and unpaired (U) residues. A large time range in the reorganization of mismatched chain configurations is characterized by a logarithmic dependence on time. This observation is quantitatively described by a kinetic model developed by Jackson. In Jackson's model the rate-limiting process in the slow annealing phase of maximizing triple-helical sequences, is the removal of strand entanglements, knots, and hairpin loops by complete unwinding of those helical stretches which stabilize the mismatched configurations. The results of the present study are briefly discussed in terms of optimum conditions for hybridization experiments and for the preparation of polynucleotide complexes commonly used to produce interferons.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160206
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  • 7
    Electronic Resource
    Electronic Resource
    Fluorescence of proteins in aqueous neutral salt solutions. I. Influence of anions (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 341-368 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of anions of neutral salts on the fluorescence emission of six proteins as well as on tryptophan and tyrosine were studied in relation to the structure of proteins. Most anions are good quenchers of tryptophyl and tyrosyl fluorescence, free or in proteins. The results with tryptophan and tyrosine indicate involvement of a collisional quenching mechanism due to agreement with Stern-Volmer law. The deactivation of fluorescence probably occurs because of the transition from singlet state to triplet state. Lehrer's modification of Stern-Volmer law was applied to proteins. The effective quenching constants ([KQ]eff) and the fraction of fluorescence available ([fa]eff) to the quencher are also calculated.In contrast to its effect on tryptophan, CH3COO- quenches tyrosyl fluorescence and ClO4- does not. The effects on fluorescence of ribonuclease and free tyrosine are similar and without any changes in emission maximum. The anions are divided into three groups based on the effect they have on tryptophan-containing proteins. (1) NO3-, NO2-, Br-, and I- have high [KQ]eff values and readily quench tryptophyl fluorescence of proteins causing a shift of emission maximum to a shorter wavelength. This change is due to the specific quenching of “exposed” tryptophan residues which are accessible to quenchers and the observed residual fluorescence is from the “buried” tryptophyls. (2) ClO4- and SCN- also quench fluorescence of tryptophan in proteins and have lower ([KQ]eff) values. In their presence the fluorescence maximum is shifted to a longer wavelength, which indicates the unfolding of a protein with [(fa)eff] = 1. (3) Cl-, CH3COO-, and SO4— do not have a direct effect on the fluorescence of tryptophan. Besides the “direct” effects, “indirect” effects on fluorophors in protein are also seen, pointing out that the neutral salts can interact in more than one manner with proteins. The effectiveness of anions in quenching fluorescence of proteins follows similar sequences which almost resemble the Hofmeister series, viz., SO4=, CH3COO- ≃ Cl- 〈 ClO4- 〈 SCN- 〈 Br- 〈 I- 〈 NO3- 〈 NO2-.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160210
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  • 8
    Electronic Resource
    Electronic Resource
    Co-oligopeptides of aromatic amino acids and glycine with a variable distance between the aromatic residues. V. pH-Dependent conformational changes in peptides containing two adjacent tryptophyl residues as evidenced by circular dichroism studies (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 437-448 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of pH upon CD spectra of H-Trp-Trp-OH, H-Trp-Trp-Gly-OH, and H-Gly-Trp-Trp-OH is investigated and data are compared with those obtained for peptides containing only one tryptophyl residue. A negative Cotton effect at around 225 nm, which in previous work has been related to an increase of the conformational rigidity in compounds having the sequence -CO-Trp-Trp, is also observed in the case of H-Trp-Trp-OH and H-Trp-Trp-Gly-OH upon deprotonation of the terminal α-amino group. These data, together with observations arising from solvent and temperature effects, give evidence that H-Trp-Trp-OH undergoes a conformational change upon going from acid to alkaline conditions, where the two aromatic side chains become conformationally more rigid relative to each other. This rigidity generates an exciton coupling between the Bb transitions of the two indoles. Hydrophobic forces, including stacking interactions, do not appear important in stabilizing this conformationally rigid structure. Rather, intramolecular electrostatic interactions (e.g., hydrogen bondings or polar interactions between the aromatic side chain and the peptide backbone) as well as interactions with the OH group(s) of the solvent, are suggested to be the salient forces. Possible structures which obey these requisites are discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160216
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  • 9
    Electronic Resource
    Electronic Resource
    Spectral analysis on the melting fine structure of λ DNA and T2 DNA (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 427-435 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The fine structure of the thermal denaturation of viral DNA's was analyzed with the spectral method established by Felsenfeld and Hirschman, and Fresco et al. A fully automated system measuring melting curves at four wavelengths at the same time was developed for this purpose. With this device, (G + C)-contents of melting components of λ DNA's were determined. The correlation between the (G + C)-content and the melting temperature of each melting component is found to be well described by the linear relationship given by Marmur and Doty. The denaturation of each component is regarded as cooperative. The Marmur-Doty relation also stands for the local denaturation of T2 DNA, which has a narrow melting range.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160215
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  • 10
    Electronic Resource
    Electronic Resource
    Relaxation times manifested by the Rouse-Zimm model in dynamic light-scattering experiments (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 461-464 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160218
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