[Regulation of two-substrate reaction by substrate analog, as analyzed by graphic methods]

The regulatory action of a substrate analogue on the two-substrate reaction has been analysed by the method of graphs. It was shown that the analogue can act not only as inhibitor but also as activator in an ordered mechanism of the two-substrate reaction. Activation of the reaction by the analogue is a consequence of its random mechanism in regard to substrates and products. This random mechanism tends to the appearance of another route in the enzymic reaction and by this route the activation of the reaction may be obtained. It was also shown, that substrate inhibition may be abolished by the analogue, if the reaction rate via analogue route is large enough. On this case the analogue competes with the substrate-inhibitor in the non-active ternary complex. For the analysis of kinetic schemes the cyclic algorithm of the graph method was applied because of its convenience for multiroute reactions. Some simplifications were proposed for the structure of graphs. The results of this analysis are applicable for interpretation of abolishing the substrate inhibition by monovalent anions for some dehydrogenases.