Analysis of the substrate inhibition of complete and partial types

Enzyme inhibition by its substrate in excess, substrate inhibition, is one of the common deviations from Michaelis–Menten kinetics, and means that the velocity curve of a reac-tion rises to a maximum as substrate concentration increases and then descends either to zero (complete inhibition) or to a non-zero asymptote (partial inhibition). Substrate inhibition is an extremely widespread phenomenon in enzyme kinetics, and plays critical regulatory roles in a number of metabolic pathways (Kaiser 1980; Kühl 1994; Reed et al. 2010). The simplest explanation of substrate inhibition implies the binding of two substrate molecules to the enzyme at the active sites and the non-catalytic inhibitory sites. Thus, determination of kinetic parameters including the dissociation constants of the substrates for the catalytic sites and inhibitory sites, and the reaction rate constants of the enzyme– substrate and enzyme–substrate–inhibitor complexes is necessary for the study on sub-strate inhibition. However, various kinetic methods for analyzing inhibition mechanism (Segel 1973; Cornish-Bowden 1974a, b; Eisenthal and Cornish-Bowden 1974; Baici 1981; Yoshino 1987) cannot be applied to substrate inhibition. In this report we describe a new graphical method for direct determination of the inhibition constants and the reactio