Mechanistic origin of the kinetic cooperativity for the ATPase activity of sarcoplasmic reticulum |
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Authors: | José A Teruel José Tudela Francisco Garcia Carmona Juan C Gomez Fernandez Francisco Garcia Canovas |
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Institution: | (1) Departamento de Bioquímica y Biología Molecular, Universidad de Murcia, Murcia, Spain |
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Abstract: | The (Ca2+-Mg2+)-ATPase from sarcoplasmic reticulum presents negative cooperativity for the hydrolysis of Mg2+-ATP at different concentration ranges of this substrate. A kinetic model is proposed according to which Mg2+-ATP may bind to three different enzymatic species present during the catalytic cycle, E (K
1=1 µM), EP.Ca2 (K
9=500 µM) and *EP (K
7=20 µM), accelerating the release of Pi. The fact that each of these species has a different affinity for Mg2+-ATP allows a significant enhancement of the rate of Pi release to the medium at the different ranges of Mg2+-ATP concentration where the enzyme shows a kinetic cooperativity. The kinetic analysis of this mechanism yields an equation which is a ratio of two cubic polynomials (3:3 rate equations) with respect to Mg2+-ATP and which may explain the negative cooperativity of the enzyme at different concentration ranges of Mg2+-ATP.Abbreviations: EGTA, ethylene glycol bis(-aminoethylether)-N,N,N,N-tetraacetic acid; I.U., international units; piruvate kinase (EC 2.7.1.40); lactate dehydrogenase (EC 1.1.1.27); ATP phosphohydrolase (EC 3.8.1.3). |
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Keywords: | (Ca2+-Mg2+)-ATPase sarcoplasmic reticulum enzyme kinetics |
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