The binding of spin-labeled derivatives of NAD+ and its structural components to pig skeletal muscle lactate dehydrogenase.

The binding of spin-labeled derivatives of NAD+ and its structural components to pig skeletal muscle lactate dehydrogenase (L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) is described. In contrast to results previously obtained with the heart muscle isozyme (Wenzel, H.R., Pfleiderer, G., Trommer, W.E., Paschenda, K. and Redhardt, A. (1976) Biochim. Biophys. Acta 452,292--301), no significant increase is observed in the binding constant of N6-SL-ADP as compared N6-SL-AMP. This different behavior can be explained by the substitution of glutamine-31 for alanine in the muscle isozyme, which has been proposed to account for the the tighter binding of NADH to the heart type. In both isozymes the binding of the binding of the spin-labeled coenzyme itself is weaker than found for its structural components.