A PM3 Quantum Chemical Study of the Pyruvate Reduction Mechanism Catalyzed by Lactate Dehydrogenase

A simulation of the lactate dehydrogenase (LDH) catalytic mechanism by means of the characterization of the global potential energy surface has been carried out by the PM3 quantum chemical method using a rather large model of the LDH active center. The minimum energy pathway for this process was established. The overall process is controlled by the hydride transfer from NADH towards pyruvate carbonyl carbon. The transition state structure that combines the hydride and proton transfers is obtained. There are two independent minima for products. In both minima the coenzyme rotation supplies the reversibility of the pyruvate-lactate interconversion. The results agree with recently published studies on transition state structure, kinetic isotope effects, and the hydride and proton transfers being coupled kinetically but not dynamically in the molecular mechanism of the LDH catalytic reaction.