[Coenzyme specificity and isoenzyme spectrum of rat brain malate dehydrogenase]

Our studies have shown that malatedehydrogenase of rat brain mitochondrial fraction (M-MDH) and soluble fraction (S-MDH) differ in respect to their coenzyme specificity. Affinity of both M-MDH and S-MDH to deamino-NAD (direct reaction) is about two times lower than toward NAD. In the reverse reaction deamino-NADH and NADH enhance the activity of M-MDH to the same extent while in the presence of deamino-NADH the activity of S-MDH is somewhat higher. The isoenzyme composition of M-MDH and S-MDH have been studied as well as the relative affinity of each isoenzyme towards deamino-NAD and NAD. Both M-MDH and S-MDH have been shown to consist of 3 isoenzymes, the second isoenzyme being the most active. The percentage of the 3-rd isoenzyme is the lowest. The coenzyme affinity of isoenzymes M-MDH and S-MDH have been shown to differ very markedly.