Understanding regulation of aspartate metabolism with a model based on measured kinetic parameters

The equation is valid for the physiological values of [Pi], [NADPH] and [NADP] listed in Table S1, and these concentrations are included in the numerical values. We assumed that the rate in the forward direction (AspP → ASA) was proportional to [AspP] and that the rate in the reverse direction (ASA → AspP) was proportional to [ASA]. These assumptions were verified a posteriori because [ASA] and [AspP] steadystate concentrations in the model were much lower than the apparent Km of ASADH for [ASA] and [AspP]. Rate constants for the forward and the reverse directions correspond to the apparent specificity constants (kcat/Km) for AspP and for ASA, respectively.