Substrate-induced enzyme dimerization. Kinetics of one- and two-substrate reactions

The catalytic activity of many oligomeric enzymes is regulated by association-dissociation processes, We studied kinetic models for mono-and bisubstrate reactions involving a catalytically active dimeric form of apr enzyme induced by its interaction with substrate. The concentration dependences of the reaction rate are different in these two cases; they also differ from the dependences predicted by the Michaelis schemes. For instance, the rate dependence on enzyme concentration proves to be nonlinear. The models also predict inhibition at higher substrate concentrations; however, a model can be put forward in which one of the two substrates is not inhibitory, For multisubstrate reactions requiring substrate-induced enzyme dimerization, the order of substrate binding to enzyme can be established by routine inhibitor analysis using various substrate analogs, as with enzymic systems exhibiting linear concentration dependences. An important point is that discrimination of the reaction models may only be effective if the reaction rates are measured over a wide range of enzyme/substrate concentrations.