valero

Title

A kinetic study of a ternary cycle between adenine nucleotides

Authors

Edelmira Valero1, Ramo ́ n Varo ́ n1 and Francisco Garcı ́a-Carmona2

Affiliations

1 Departamento de Qu ́ımica-F ́ısica, Escuela Polite ́cnica Superior de Albacete, Universidad de Castilla-La Mancha, Albacete, Spain 2 Departamento de Bioqu ́ımica y Biolog ́ıa Molecular A, Facultad de Biolog ́ıa, Universidad de Murcia, Spain

Abstract

In the present paper, a kinetic study is made of the behavior of a moiety- conserved ternary cycle between the adenine nucleotides. The system con- tains the enzymes S-acetyl coenzyme A synthetase, adenylate kinase and pyruvate kinase, and converts ATP into AMP, then into ADP and finally back to ATP. l-Lactate dehydrogenase is added to the system to enable continuous monitoring of the progress of the reaction. The cycle cannot work when the only recycling substrate in the reaction medium is AMP. A mathematical model is proposed whose kinetic behavior has been analyzed both numerically by integration of the nonlinear differential equations describing the kinetics of the reactions involved, and analytically under steady-state conditions, with good agreement with the experimental results being obtained. The data obtained showed that there is a threshold value of the S-acetyl coenzyme A synthetase⁄adenylate kinase ratio, above which the cycle stops because all the recycling substrate has been accumulated as AMP, never reaching the steady state. In addition, the concept of adenylate energy charge has been applied to the system, obtaining the enabled values of the rate constants for a fixed adenylate energy charge value and vice versa.

Journal

FEBS Journal 273 (2006) 3598–3613

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Global parameters

Local parameters

Assignment rules

Rate rules

Algebraic rules