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  • Springer  (18)
  • 1980-1984  (18)
  • 1960-1964
  • 1955-1959
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  • 1
    ISSN: 1573-4943
    Keywords: cyclic AMP derivatives ; affinity labels ; chemical modification of enzymes ; nucleotide affinity labels ; cAMP phosphodiesterase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The syntheses of two potential cAMP affinity lables, 1,N 6-(3-iodopropyleno)adenosine 3′,5′-cyclic-monophosphate and 2′-O-(2-iodo-3-hydroxypropyl) adenosine 3′,5′-cyclic-monophosphate, by a two-step chemical procedure are described. TheN 6- and 2′-O-allyl intermediates were prepared selectively by alkylation of cAMP in organic and alkaline aqueous solutions, respectively. Treatment of theN 6-allyl derivative withN-iodosuccinimide resulted in iodine addition to the double bond and cyclization to theN 1 position of the purine ring. The iodohydrin analog was synthesized by reaction of 2′-O-allyl-cAMP with potassium iodide and thallium trichloride in acetate buffered solution. The products were isolated by column chromatography and characterized by thin-layer chromatography, elemental analysis, and ultraviolet,13C, and1H NMR spectroscopy. The cAMP analogs were found to react with lysine and cysteine. Both cAMP derivatives were tested for their reaction with the low-K m cAMP phosphodiesterase of human platelets. The ribose-substituted analog functioned as a competitive inhibitor (K I =0.72 μM) and caused a time-dependent irreversible inactivation of the phosphodiesterase. In contrast, the purine-substituted derivative acted neither as a reversible competitive inhibitor nor as an irreversible inactivator of the enzyme. These results indicate the specificity of these potential cAMP analogs in their interaction with the phosphodiesterase.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 42 (1980), S. 861-870 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A mathematical model of prothrombin activation is being proposed which includes the feedback mechanism of thrombin and the alteration of factor V by thrombin. This model is in good agreement with experimental data for the dependence of the rate of thrombin formation on the concentrations of factors V and X a . In particular, it correctly predicts the existence and location of a maximum in both of these cases.
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  • 3
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In the study of chemical modification of enzymes and other biologically active proteins, plots of fractional residual activity as a function of number of groups modified per enzyme molecule are often used to establish a correlation between the chemical modification and enzyme inactivation reactions and to determine the stoichiometry of the modification reaction. This paper presents a critical examination of the underlying theoretical framework of such graphs. Whereas these plots are usually presented as linear functions, it is shown here that the general equation describing the relationship between inactivation and modification contains an exponential term; therefore, in the general case, the plot is actually a curve. It is suggested that caution be exercised in the interpretation of such plots and that equations such as those derived in the text be used to fit theoretical curves to the data, in order to maximize the information gained from chemical modification experiments.
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  • 4
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We describe a portable, non-motorized device for delivering a tracer dye into seawater under field conditions. Dye is ejected at a constant flow rate over a period of tens of minutes. The ejector works in a wide range of ambient pressures without external energy requirements. The flow rate is adjusted simply by varying the length of the delivery tube. The dye streams permitted observations of the upcurrent and downcurrent flow regimes for a filter-feeding crinoid (Comanthus bennetti) living at a depth of 8 m on a coral reef. The results indicate that the crinoid may enhance the rate of particle capture by changing the scale of turbulence in the water passing through the mesh of the filtration fan.
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  • 5
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A variety of 3H-labelled ribosomal gene probes were hybridized in situ to the nascent transcripts of lampbrush chromosomes from the crested newt, Tritums cristatus carnifex. The probes were from Xenopus laevis and included rDNA isolated by CsCl gradient centrifugation, recombinant plasmids and purified restriction fragments of rDNA. All the probes gave essentially the same result. About 10–15 loop pairs were distinctly labelled in each preparation, almost all of them located on the heteromorphic arms (HTAs) of chromosome 1. Ribosomal gene probes were also hybridized in situ to the DNA of denatured mitotic chromosomes from some of the individuals used to provide lampbrush preparations. Minor, scattered sites of hybridization were found in the HTAs, but the main clusters of ribosomal genes were found on chromosomes 6 and/or 9, in agreement with previous determinations of nucleolus organizer position in this species. However, the nucleolus organizers were not sites of labelled loops in lampbrush transcript hybridizations. — We have incubated isolated lampbrush-stage nuclei in media containing α-amanitin and labelled RNA precursors. Although extrachromosomal nucleolar genes incorporated label, supposedly due to transcription by RNA polymerase I, no lampbrush loops were labelled. — It appears that in T. c. carnifex there are ribosomal gene sequences at the main nucleolus organizers and at a number of sites scattered along the HTAs. The ribosomal genes at the nucleolus organizers are not extended in the form of actively transcribing loops unlike the ribosomal sequences on the HTAs, which are heavily labelled in transcript hybridization. The ribosomal sequences on the HTAs appear not to be transcribed by the same RNA polymerase that transcribes the ribosomal genes of extrachromosomal nucleoli.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Planta 149 (1980), S. 318-320 
    ISSN: 1432-2048
    Keywords: Coccochloris ; CO2 fixation ; Photosynthesis (bluegreen alga)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Air-grown cells of the cyanobacterium, Coccochloris peniocystis Kutz were exposed to [14C] bicarbonate in the light for periods of 0.5 to 2.0 s followed by longer exposures to unlabelled bicarbonate. Although C4 acids are among the initial products of photosynthesis, the kinetics of tracer movement during the pulse-chase experiments demonstrate that the principal mechanism of CO2 fixation in this alga is the C3-pathway.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 59 (1984), S. 101-111 
    ISSN: 1573-4919
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Adenosine diphosphate (ADP) is known to induce platelet shape change, aggregation and fibrinogen binding, followed by secretion. These processes are mediated by the binding of ADP to an externally oriented protein of the platelet plasma membrane. An affinity analog of ATP, a competitive inhibitor of the action of ADP, has been utilized to probe the structure and function of this receptor. FSBA (5′-p-fluorosulfonylbenzoyl adenosine) covalently modifies a single protein in intact platelets with Mr = 100 000 and concomitantly inhibits platelet shape change, aggregation and fibrinogen binding. Studies on platelet membranes demonstrate non-covalent association of ADP-binding protein with actin which is also labeled by FSBA but only in isolated membranes. This finding suggests a structural and functional coupling of the receptor to the contractile process. The putative ADP receptor covalently modified with FSBA is cleaved by chymotrypsin, a process that reverses the inability of the platelets to bind fibrinogen. Thus, the Mr = 100 000 polypeptide may be involved in the proteolytic exposure of fibrinogen binding sites on the platelet surface. The ability of FSBA to inhibit platelet aggregation and fibrinogen binding by prostaglandin H2 derivatives and epinephrine suggest that ADP is involved in these processes. However, the interaction is not at the receptor level since shape change, stimulated by PGH2 derivatives and yohimbine (epinephrine antagonist) binding are unaffected by FSBA. Finally, the action of ADP to inhibit PGE1- or PGI2-stimulated adenylate cyclase appears to be mediated by a receptor distinct for the protein modified by FSBA.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The protein journal 2 (1983), S. 171-185 
    ISSN: 1573-4943
    Keywords: blood coagulation factor V ; snake venoms ; thrombocytin ; Russell's viper venom protease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Thrombin activation of factor V constitutes an important feedback reaction in the regulation of coagulation. We therefore examined the details of activation of bovine factor V by two purified snake venom proteolytic enzymes, factor V-activating protease from Russell's viper venom and a platelet-aggregating enzyme, thrombocytin, fromBothrops atrox venom. The reactions were followed by changes in factor V coagulant activity, immunoelectrophoresis, and electrophoresis of radiolabeled factor V in sodium dodecylsulfate under reducing conditions. When factor V (M r 330,000) was exposed to factor V-activating protease at an enzyme-to-substrate ratio of 1:35 at 37°, cleavage occurred in 1 min, with formation of an intermediate (M r 250,000) coincident with a nine-fold activity increase. By 2 min, additional cleavage occurred, with disappearance of the intermediate and formation of two final fragments (M r 150,000 and 100,000) but no further change in coagulant activity. The concentration of these components remained unchanged from 5 to 15 min. Immunoelectrophoresis against antiserum directed against factor V confirmed cleavage of the molecule. Incubation of factor V with thrombocytin at 37° for 1 min resulted in a four-fold increase of factor V activity, with the formation of an intermediate (M r 220,000). By 2 min, a 7.5-fold activation was found, with a decline in the concentration of the intermediate; the predominant species hasM r =130,000. At 5 min the intermediate disappeared and a second, final fragment ofM r of ∼150,000 appeared without further change in coagulant activity. Immunoelectrophoresis again confirmed selective proteolysis. Thus, incubation of factor V-activating protease or thrombocytin with factor V results in different molecular alterations associated with an increase in the coagulant activity of this clotting factor.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Planta 153 (1981), S. 210-216 
    ISSN: 1432-2048
    Keywords: Asparagus ; 5,5-Dimethyloxazolidine-2,4-dione ; Mesophyll ; Photosynthesis ; pH, intracellular
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The intracellular pH of isolated, photosynthetically active mesophyll cells of Asparagus sprengeri Regel has been determined, in the light and dark, by the distribution of the weak acid 5,5-dimethyl-[2-14C]oxazolidine-2,4-dione ([14C]DMO) between the cells and the liquid medium. [14C]DMO was taken up rapidly, reaching equilibrium in 7–10 min of incubation, but was not metabolized by the cells, and intracellular binding of the compound was minimal. The intracellular pH, measured at saturating light fluence and 1.5 mM sodium bicarbonate, was found to remain relatively constant at 6.95–7.21 over the external pH range of 5.5–7.2. Illumination of the cells increased the intracellular pH compared to dark controls. The pH of the cytoplasm, excluding and including the chloroplasts (“cytoplasmic” and “bulk cytoplasmic”, respectively) was calculated from the experimentally derived intracellular [14C]DMO concentration and estimates of the vacuolar, chloroplastic and cytoplasmic volumes. The calculated cytoplasmic pH was similar in the light and dark, being 7.75 and 7.74, respectively, while the calculated pH of bulk cytoplasm was 7.85 in the light and 7.49 in the dark. Theoretical analysis indicated that intracellular pH is a good indicator of changes in the bulk cytoplasmic pH but insensitive to changes in vacuolar pH. The external pH optimum for photosynthesis (O2 evolution) of isolated Asparagus cells was pH 7.2. At pH 8.0 photosynthesis was inhibited by 30% and at pH 5.25 by 45%. Inhibition at alkaline pH may be the result of a decrease in the pH gradient between the cells and the medium, causing CO2 limitation in the cell. At acid pH, decrease in internal pH caused by substantial accumulation of inorganic carbon may account for the loss in photosynthetic activity.
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  • 10
    ISSN: 1573-4943
    Keywords: purine nucleotide derivatives ; affinity labels ; chemical modification of enzymes ; nucleotide affinity labels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two new adenosine analogs, 2′-(2-bromoethyl) adenosine monophosphate and 3′-(2-bromoethyl) adenosine monophosphate, were synthesized, purified by semipreparative high-pressure liquid chromatography, and completely characterized. A new synthesis of 5′-(2-bromoethyl) adenosine monophosphate is presented which facilitates the preparation of radioactive reagent with label either in the ethyl group or the purine ring of the nucleotide derivative. The reactive moiety of these derivatives, a bromoalkyl group, has the ability to react with the nucleophilic side chains of several amino acids. The second-order, pH-independent rate constants for reaction with the side chains of the amino acids cysteine, lysine, histidine, and tyrosine were determined as 3×10−4, 6×10−6, 3×10−7, and 〈1×10−7 M−1 sec−1, respectively. These data could be use in estimating the rate enhancement observed in modification of a protein by these affinity-labeling reagents. 5′-(S-(2-hydroxyethyl)cysteine) adenosine monophosphate, the derivative expected from exhaustive digestion of protein in which a cysteinyl residue is modified by 5′-(2-bromoethyl) adenosine monophosphate, and S-2-hydroxyethyl)cysteine, the derivative anticipated upon acid hydrolysis of such a modified protein, were synthesized, characterized, and their elution positions from an amino acid analyzer determined. These bromoethyl AMP derivatives are potential affinity labels for enzymes that bind 2′-, 3′-, or 5′-nucleotides such as TPN, coenzyme A, or ADP, respectively.
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