NAD(+) NADP(+)-DEPENDENT MALIC ENZYME - EVIDENCE OF A NADP(+) PREFERRING ACTIVITY IN HUMAN SKELETAL-MUSCLE/

The L-malate NAD(P)(+) oxidoreductase (decarboxylating) E.C.1.1.1.39 w as purified from human skeletal muscle; the specific activity estimate d in the presence of NADP(+) as coenzyme was similar to 15 mu mol/min/ mg. The apparent V-max values for NAD(+) (similar to 8 mu mol/min/mg) and NADP(+) (similar to 16 mu mol/min/mg) show that the enzyme (in thi s tissue) is more active in the presence of NADP(+). This observation was confirmed by the estimation of enzymatic activity in competition e xperiments where both NAD(+) and NADP(+) were used together as coenzym es. The absence of pyruvate carboxylation and of oxalacetate decarboxy lation activities demonstrates that the enzyme studied is E.C.1.1.1.39 . In addition, the apparent K-m values for NAD(+) and NADP(+) were cal culated (15 and 0.05 mM, respectively). This paper provides the first demonstration of a NADP(+) preferring activity of the enzyme in human skeletal muscle, (C) 1995 Academic Press, Inc.