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Titolo:
RAT-LIVER PHOSPHORIBOSYLPYROPHOSPHATE SYNTHETASE IS ACTIVATED BY FREEMG2+ IN A MANNER THAT OVERCOMES ITS INHIBITION BY NUCLEOTIDES
Autore:
SONODA T; ISHIZUKA T; ISHIJIMA S; KITA K; AHMAD I; TATIBANA M;
Indirizzi:
CHIBA UNIV,SCH MED,DEPT BIOCHEM,CHUO KU,INOHANA 1-8-1 CHIBA 2608670 JAPAN
Titolo Testata:
Biochimica et biophysica acta. Protein structure and molecular enzymology
fascicolo: 1-2, volume: 1387, anno: 1998,
pagine: 32 - 40
SICI:
0167-4838(1998)1387:1-2<32:RPSIAB>2.0.ZU;2-K
Fonte:
ISI
Lingua:
ENG
Soggetto:
COMPLETE CDNA SEQUENCE; ESCHERICHIA-COLI; PYROPHOSPHATE SYNTHETASE; SUBUNIT-II; DIPHOSPHATE SYNTHETASE; SALMONELLA-TYPHIMURIUM; CATALYTIC SUBUNITS; PURIFIED ENZYME; IDENTIFICATION; BINDING;
Keywords:
NUCLEOTIDE SYNTHESIS; PHOSPHORIBOSYLPYROPHOSPHATE SYNTHETASE; NUCLEOTIDE INHIBITION; FREE MG2+ ACTIVATION; ALLOSTERIC EFFECT; ANTAGONISTIC EFFECT;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
36
Recensione:
Indirizzi per estratti:
Citazione:
T. Sonoda et al., "RAT-LIVER PHOSPHORIBOSYLPYROPHOSPHATE SYNTHETASE IS ACTIVATED BY FREEMG2+ IN A MANNER THAT OVERCOMES ITS INHIBITION BY NUCLEOTIDES", Biochimica et biophysica acta. Protein structure and molecular enzymology, 1387(1-2), 1998, pp. 32-40

Abstract

Phosphoribosylpyrophosphate synthetase is activated by Pi and free Mg2+ as an essential activator and inhibited by nucleotides, especially ADP and GDP. The rat liver enzyme is a complex aggregate of two highlyhomologous catalytic subunits (PRS I and PRS II) and two associated proteins (PAP39 and PAP41), PRS I is more sensitive to inhibition by ADP and GDP than is PRS II. The native liver enzyme showed a weaker sensitivity to inhibition by nucleotides than expected from its composition. To further understand the regulation of the liver enzyme, kinetic studies of each subunit component and the liver enzyme regarding Mg2+ activation and inhibition by ADP and GDP were carried out. Assay conditions were designed to keep free Mg2+ at constant concentrations. (1) GDP, as MgGDP, did not affect the apparent K-m values of PRS I for MgATP and ribose-5-phosphate but did dramatically increase the apparent K-a value for free Mg2+. (2) In contrast, ADP, as MgADP, increased the K-m value for MgATP of PRS I as well as the K-a value for free Mg2+. (3) High concentrations of free Mg2+ almost completely nullified the inhibitory effect of MgGDP and partly that of MgADP on PRS I. (4) At low free Mg2+ concentrations within the physiological range, inhibition bythe nucleotides is of physiological significance and conversely, variation in free Mg2+ concentrations critically affects the enzyme activity in the presence of inhibitory nucleotides. (5) The response of PRS II and the native liver enzyme is similar to that of PRS I, while the effects of MgGDP and MgADP were smaller than that on PRS I. (6) We propose that MgGDP binds to a regulatory site of PRS I and PRS II and MgADP to the substrate MgATP site and also the regulatory site. The allosteric interaction of the regulatory site and the Mg2+ binding site is also considered. (C) 1998 Elsevier Science B.V. All rights reserved.

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Documento generato il 07/04/20 alle ore 22:44:41