A mathematical model for the adenylosuccinate synthetase reaction involved in purine biosynthesis

Development of the mathematical models that adequately describe biochemical reactions and molecular-genetic mechanisms is one of the most important tasks in modern bioinformatics. Because the enzyme adenylosuccinate synthetase (AdSS) has long been extensively studied, a wealth of kinetic data has been accumulated.

We describe a mathematical model for the reaction catalyzed by AdSS. The model's parameters were fitted to experimental data obtained from published literature. The advantage of our model is that it includes relationships between the reaction rate, the concentrations of three substrates (GTP, IMP and ASP), the effects of five inhibitors (GMP, GDP, AMP, ASUC and SUCC), and the influence of Mg2+ ions.

Our model describes the reaction catalyzed by AdSS as a fully random process. The model structure implies that each of the inhibitors included in it is only competitive to one of the substrates. The model was tested for adequacy using experimental data published elsewhere. The values obtained for the parameters are as follows: Vmax = 1.35.10-3 mM/min, KmGTP = 0.023 mM, KmIMP = 0.02 mM, KmASP = 0.3 mM, KiGMP = 0.024 mM, KiGDP = 8.10-3 mM, KiAMP = 0.01 mM, KiASUC = 7.5.10-3 mM, KiSUCC = 8 mM, KmMg = 0.08 mM.