Are chemical transformations in an enzyme-substrate complex reversible? Experience of the fractionation of isotopes in enzymatic reactions

The complete kinetic analysis of two alternative schemes of the enzymatic reactions is carried out with an account of the equilibrium in the SE↔PE complex and SE→PE irreversible transformation (S=substrate, E=enzyme, P=product). The kinetic equations for the velocity constants and isotope fractionation coefficients are obtained. It is shown that the isotope fractionation is accomplished in the course of the irreversible chemical reaction on the account of the kinetic isotope effect. The isotope distribution observed thereby imitates the thermodynamic equilibrium