Allosteric enzyme models and their analysis by the theory of graphs.

Abstract Possible cooperative models, intended for the description of the properties of allosteric enzymes, have been studied for the simplest case of the dimeric protein. Both the “indirect” cooperativity used by Monod et al,1 and the “direct” cooperativity determined by the direct interaction of active sites have been investigated. The method of the theory of graphs is used for the calculation of the effect of the allosteric inhibitor and of the competitive activator on the enzyme activity. The results of calculations agree qualitatively with the data obtained by Gerhart and Pardee 4 for aspartate transcarbamylase (carbamoylphosphate: L -aspartate carbamoyltransferase, EC 2.1.3.2). The models are described by equations containing a smaller number of consants than the model of Monod et al.1.