The effects of adenine nucleotides on NADH binding to mitochondrial malate dehydrogenase

The effects of adenine nucleotides on initial velocity and NADH binding have been studied with the malate dehydrogenase reaction. ATP, ADP, and AMP were inhibitors competitive with NADH and uncompetitive with oxaloacetate but caused only 50–60% inhibition at saturating concentrations. Direct fluorescence titrations indicated that saturating concentrations of the adenine nucleotides displaced 50–60% of the bound NADH from enzyme-NADH complex. Adenine and adenosine had no inhibitory effect but ADP-ribose caused complete inhibition and NADH dissociation. The possible mechanistic basis for these results and their physiological implications are discussed.