Kinetics of thermal inactivation of lactate dehydrogenase from rabbit muscle

The kinetics of thermal inactivation of rabbit muscle lactate dehydrogenase at different temperatures has been studied using the kinetic method for the substrate reaction during irreversible inhibition of enzyme activity previously described by Tsou [Adv. Enzymol. Relat. Areas Mol. Biol. (1988), 61, 381-436]. The results show that thermal inactivation of the enzyme is an irreversible reaction. Microscopic rate constants were determined for thermal inactivation of the free enzyme and the enzyme-substrate complex. The inactivation rate constant of the free enzyme is much larger than the rate constant of the enzyme-substrate complex. The results suggest that the presence of the substrate has a certain protective effect against thermal inactivation of the enzyme.