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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined multiple cofactor usage by yeast tRNA ligase in splicing in vitro. The ligase mechanism of action requires expenditure of two molar equivalents of nucleotide cofactor per mole of tRNA product. Recent evidence (Westaway, S.K., Belford, H.G., Apostol, B.L., Abelson, J., and Greer, C.L. (1993) J. Biol. Chem. 268, 2435-2443) demonstrated that the ligase-associated kinase activity is more efficient with GTP as cofactor than with ATP. Employing a ligase fusion construct with dihydrofolate reductase (Apostol, B.L., Westaway, S.K., Abelson, J., and Greer, C.L. (1991) J. Biol. Chem. 266, 7445-7455) for purposes of enzyme purification, we performed joining assays demonstrating that ATP and GTP are the most effective combination of cofactors. ATP was essential to the joining reaction, while UTP, CTP, or ATP replaced GTP inefficiently. Specific and functionally independent binding sites were confirmed for ATP and GTP by direct binding measurement. A third site was implicated in UTP- and CTP-ligase interactions. Comparison of binding constants with Kapp values determined for nucleotide-dependent joining suggested both that nucleotide triphosphate binding may be limiting in tRNA joining and that tRNA ligation occurs most efficiently using GTP for the kinase reaction and ATP as the adenylylate synthetase cofactor.
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PMID:Multiple nucleotide cofactor use by yeast ligase in tRNA splicing. Evidence for independent ATP- and GTP-binding sites. 842 19

The contractile protein actin contains one mole of firmly bound nucleotide and a number of divalent cations bound with different affinities. During recent years evidence for a second nucleotide interacting site on actin has been reported. Therefore, a specific search for the presence of a second nucleotide-interacting site on actin was undertaken. For this purpose G- and F-actin or actin in complex with deoxyribonuclease I (DNase I) was passed over ADP-agarose which was found to retain all three forms of actin. Nucleotide bound to the high affinity site of actin did not exchange during passage and retention to agarose-immobilized ADP, thus indicating the presence of a second nucleotide interacting site. This site was found to be equally accessible in G- and F-actin and in the actin-DNase I complex, whereas DNase I alone passed unretained through this column. A number of nucleotides and phosphorylated compounds were tested for their ability to compete with immobilized ADP for actin interaction. It was found that all forms of actin are liberated only by high concentrations (5mM) of ADP, ATP and NADH, by 1mM CTP and ITP, and by high salt concentrations (150mM NaCl). Since it was found that EDTA- and heat-treated actin were also retained on ADP-agarose, we conclude that this second nucleotide interacting site is of limited specificity, low affinity, and not dependent on the native configuration of actin. It exhibits characteristics of an unspecific, polyanionic site, but may represent the low affinity phosphate binding site.
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PMID:Evidence that the presumptive second nucleotide interacting site on actin is of low specificity and affinity. 848 39

We have utilized DSC and high pressure FTIR spectroscopy to study the specificity and mechanism by which ATP protects actin against heat and pressure denaturation. Analysis of the thermograms shows that ATP raises the transition temperature Tm for actin from 69.6 to 75.8 degrees C, and the calorimetric enthalpy, deltaH, from 680 to 990 kJ/mole. Moreover, the peak becomes sharper indicating a more cooperative process. Among the other nucleotide triphosphates, only UTP increases the Tm by 2.5 degrees C, whereas GTP and CTP have negligable effects; ADP and AMP are less active, increasing the Tm by 2.1 and 1.6 degrees C, respectively. Therefore, gamma phosphate plays a key role in this protection, but its hydrolysis is not implicated since the nonhydrolysable analogue of ATP, ATP-PNP have the same activity as ATP. FTIR spectroscopy demonstrates that ATP also protects actin against high pressure denaturation. Analysis of the amide I band during the increase in pressure clearly illustrates that ATP protects particularly a region rich in beta-sheets of the actin molecule.
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PMID:Effects of nucleotides on the denaturation of F actin: a differential scanning calorimetry and FTIR spectroscopy study. 924 36

CDP-2,3-di-O-geranylgeranyl-sn-glycerol synthase (CDP-archaeol synthase) activity was discovered in the membrane fraction of the methanoarchaeon Methanothermobacter thermoautotrophicus cells. It catalyzed the formation of CDP-2,3-di-O-geranylgeranyl-sn-glycerol from CTP and 2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate (unsaturated archaetidic acid). The identity of the reaction product was confirmed by thin layer chromatography, fast atom bombardment-mass spectroscopy, chemical analysis, and by UV spectroscopy. One mole of the product was formed from approximately 1 mol of each of the reactants. The enzyme showed maximal activity at pH 8.5 and 55 degrees C in the presence of Mg(2+) and K(+) ions. By in vivo pulse labeling of phospholipids with (32)P(i), CDP-archaeol was found to be an intracellular intermediate. A cell-free homogenate of M. thermoautotrophicus, when incubated with l-serine, converted the product of CDP-archaeol synthase reaction to a product with the same chromatographic mobility as archaetidylserine. It was concluded from these results that both CDP-archaeol and CDP-archaeol synthase were involved in cellular phospholipid biosynthesis. Among various synthetic substrate analogs, both enantiomers of unsaturated archaetidic acid possessing geranylgeranyl chains showed similar levels of activity, while archaetidic acid with saturated or monounsaturated isoprenoid or straight chains was a poor substrate, despite having the same stereostructure as the fully active substrate. The ester analogs with geranylgeranioyl chains showed significant activities. These results suggest that the enzyme dose not recognize ether or ester bonds between glycerophosphate and hydrocarbon chains nor the stereostructure of the glycerophosphate backbone but mainly targets substrates with geranylgeranyl chains.
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PMID:CTP:2,3-di-O-geranylgeranyl-sn-glycero-1-phosphate cytidyltransferase in the methanogenic archaeon Methanothermobacter thermoautotrophicus. 1096 Apr 77

The 2',3'-dialdehyde derivative of ATP (dial-ATP) has been shown to be an affinity label for the ATP binding site of the H(+)-ATPase from tonoplast of etiolated mung bean seedlings (Vigna radiata L.). The dial-ATP caused marked inactivation of enzymatic activities of both membrane-bound and soluble ATPase and its associated proton translocation. The inactivation was reversible, but could be stabilized by NaBH(4). The sodium dodecyl sulfatepolyacrylamide gel electrophoresis pattern revealed that the dial-ATP binding site was in the large (A) subunit of ATPase. The inhibition could be substantially protected by its physiological substrate ATP, pyrophosphate, and nucleotides in the decreasing order: ATP > pyrophosphate > ADP = AMP > GTP > CTP = UTP. A Lineweaver-Burk plot showed that the mode of inhibition was competitive with respect to ATP. Loss of ATPase activity followed pseudo-first order kinetics with a K(i) of 4.1 millimolar, a minimum inactivation half-time of 20 seconds, and a pseudo-first order rate constant of 0.035 s(-1). The double logarithmic plot of apparent rate constant versus dial-ATP concentration gave a slope of 0.927, indicating that inactivation results from reaction of at least one lysine residue at the catalytic site of the large subunit. Labeling studies with [(3)H]dial-ATP indicate that the incorporation of approximately 1 mole of dial-ATP per mole ATPase is sufficient to completely inhibit the ATPase. A working model of nonequivalent subunits for enzymatic mechanism of vacuolar ATPase is suggested.
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PMID:Inhibition of tonoplast ATPase by 2',3'-dialdehyde derivative of ATP. 1666 47


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