Comparison of the Kinetic Behavior toward Pyridine Nucleotides of NAD+-Linked Dehydrogenases from Plant Mitochondria

In this article we compare the kinetic behavior toward pyridine nucleotides (NAD(+), NADH) of NAD(+)-malic enzyme, pyruvate dehydrogenase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and glycine decarboxylase extracted from pea (Pisum sativum) leaf and potato (Solanum tuberosum) tuber mitochondria. NADH competitively inhibited all the studied dehydrogenases when NAD(+) was the varied substrate. However, the NAD(+)-linked malic enzyme exhibited the weakest affinity for NAD(+) and the lowest sensitivity for NADH. It is suggested that NAD(+)-linked malic enzyme, when fully activated, is able to raise the matricial NADH level up to the required concentration to fully engage the rotenone-resistant internal NADH-dehydrogenase, whose affinity for NADH is weaker than complex I.