[Conformational isomerization of lactate dehydrogenase complexes formed by pyruvate and coenzyme analogs]

The kinetics of LDH-catalyzed reduction of pyruvate involving APADH were studied. It was shown that under conditions of a single turnover reaction the first order rate constant is equal to 37+/-4 sec-1. The reaction rate (vo) did not change when a deutero-coenzyme was used. The relationship between vo and pyruvate concentration is hyperbolic. It is concluded that isomerization of the ternary LDH-APADH-pyruvate complex limits the reaction rate. The spectral properties and the kinetics of formation and dissociation of abortive LDH complexes with pyruvate and NAD analogs (APAD and PAAD) were studied. The participation of the carboxamide group of NAD in conformational isomerization of the LDH-NADH-pyruvate and LDH-NAD-pyruvate complexes was studied.