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

Yeast phenylalanyl-tRNA synthetase, an enzyme with an alpha2beta2 structure, has two active sites for phenylalanine, tRNAphe, phenylalanyladenylate and phenylalanyl-tRNAphe. Determination of phenylalanine binding properties to the free enzyme by equilibrium dialysis shows that only one mole of amino acid binds per mole of enzyme, i.e. absolute negative cooperativity. Binding of the amino acid in the presence of tRNA or of ATP and PPi unmasks the second phenylalanine binding site. The difference between the affinities at the tight and loose binding sites under such conditions is about 10--15. Titration of phenylalanyladenylate sites by the burst of ATP consumption shows the formation of a (enzyme-phenylalanyladenylate)2 complex in the presence of pyrophosphatase; however, the two sites differ widely in their affinity as shown by dialysis experiments. Measurements of hydrolysis rates of enzyme-bound phenylalanyladenylate suggests that when only the high-affinity adenylate site is occupied, the other protomer can still bind phenylalanine and ATP (in the presence of phenylalanine). Two moles of Phe-tRNAphe bind to the enzyme with a very high affinity (Kd less than 48 nM). The presence of millimolar concentrations of ATP, phenylalanine and pyrophosphate triggers negative cooperativity and under these conditions only one mole of Phe-tRNAphe is bound per mole of enzyme with a Kd value of 0.15 muM. The present results give support to interprotomer catalytic cooperativity in the mechanism of action of yeast phenylalanyl-tRNA synthetase.
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PMID:Non-equivalence of the sites of yeast phenylalanyl-tRNA synthetase during catalysis. 32 9

ATP phosphorylates the regulatory center of E. coli inorganic pyrophosphatase with the resultant 1,5-fold increase in the activity of the enzyme. The maximal incorporation of the ATP gamma-group into pyrophosphatase is 3 moles per mole of the protein. Pi likewise phosphorylates the enzyme regulatory center and lowers the pyrophosphatase activity by 10-15%. The ATP- and Pi-mediated phosphorylation processes are interrelated; ATP prevents phosphorylation by Pi and brings about rapid dephosphorylation of Pi-modified protein.
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PMID:[Phosphorylation as a method of regulating inorganic pyrophosphatase activity in E. coli. I. Phosphorylation and enzyme activation induced by ATP]. 300 99

Incubation of inorganic pyrophosphate from baker's yeast with phosphate and MgCl2 in the presence of fluoride results in a gradual inactivation of the enzyme concomitant with incorporation of PP1 (about 2 moles per mole) into the protein. The rate constant for this process shows an increase with a rise in concentrations of the three reagents, the maximal value of inactivation being 0.11 min-1. The bound PP1 is not separated by gel-filtration. The rate of spontaneous degradation of the enzyme-pyrophosphate complex and the nature of EDTA and Mg2+ effects are similar to those for the analogous compound obtained by inhibition of PP1 hydrolysis by fluoride. The data obtained suggest that during PP1 synthesis and hydrolysis by pyrophosphatase fluoride stabilizes the same intermediate of the enzyme with pyrophosphate.
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PMID:[Stable compound of inorganic pyrophosphatase with pyrophosphate obtained by a fluoride-mediated reaction with phosphate]. 611 33

A comparative study of phosphorylation of native dimeric and artificial monomeric forms of inorganic pyrophosphatase and its fluoride-stabilized complex with PPi has been carried out. The maximal incorporation of Pi for the dimeric and monomeric proteins is 0.5 and 1 mole per mole of subunit, respectively. The saturation kinetic curves are suggestive of strong positive cooperative interactions. The value of the Hill coefficient (5.5) for the free dimeric enzyme drastically changes upon the active center blockage and/or transition to the monomeric enzyme. Acceleration of dephosphorylation induced by Pi in the presence of Mg2+ is observed only in the case of the dimeric protein. The data obtained indicate that phosphorylation of native dimeric pyrophosphatase occurs according to a "flip-flop" mechanism; the Pi binding in the active center exerts a strong influence on individual steps of the reaction.
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PMID:[Cooperative mechanism of phosphorylation of the monomeric and dimeric forms of inorganic pyrophosphatase from baker's yeast]. 612 24