Kinetic behaviour of soluble and mitochondrial bound lactate dehydrogenase

Rabbit liver mitochondrial fraction shows lactate dehydrogenase activity. The kinetic behaviour of mitochondrial bound enzyme fits a bibi sequential type mechanism as well as the cytosolic rabbit liver lactate dehydrogenase. The bound enzyme has greater values of Km(NADH) and Km(pyruvate) than the soluble one, suggesting that binding induces a decrease in the affinity of both substrates. The behaviour of the free and the mitochondrial-bound enzyme is of the Michaelis-Menten type, but the kinetics of a mixture of rabbit liver cytosolic and mitochondrial-bound lactate dehydrogenase is sigmoidal, suggesting that a cooperative phenomenon takes place.