The enzyme activity allosteric regulation model based on the composite nature of catalytic and regulatory sites concept

A new kinetic model of enzymatic catalysis is proposed, which postulates th at enzyme solutions are equilibrium systems of oligomers differing in the n umber of subunits and in the mode of their assembly. It is suggested that t he catalytic and regulatory sires of allosteric enzymes are of composite na ture and appear as a result of subunits joining. Two possible joining modes are postulated at each oligomerization step. Catalytic site may arise on o ligomer formed only by one of these modes. Effector acts by fastening toget her components of certain oligomeric form and increases the life time of th is form. It leads to a shift of oligomer equilibrium and increases a propor tion of effector-binding oligomers. Effectors-activators bind the oligomers carrying composite catalytic sites and effectors-inhibitors bind the oligo mers, which do not carry active catalytic sites. Thus, catalytic activity c ontrol in such system is explained by effector-induced changes of a catalyt ic sites number, but not of a catalytic site activity caused by changes of subunit's tertiary structure. The postulates of the model do not contradict available experimental data a nd lead to a new type of general rate equation, which allows to describe an d understand the specific kinetic behavior of allosteric enzymes as well as Michaelis type enzymes. All known rate equations of allosteric. The equation was tested by modeling the kinetics of human erythrocyte phosp hofructokinase. It enabled to reproduce quantitatively the 66 kinetic curve s experimentally obtained for this enzyme under different reaction conditio ns.