Regulation of coenzyme utilization by mitochondrial NAD(P)-dependent malic enzyme

Abstract

1. 1. Skeletal muscle mitochondrial NAD(P)-dependent malic enzyme [EC 1.1.1. 39, l-malate: NAD + oxidoreductase (decarboxylating)] from herring could use both coenzymes, NAD and NADP, in a similar manner. 2. 2. The coenzyme preference of mitochondrial NAD(P)-dependent malic enzyme was probed using dual wavelength spectroscopy and pairing the natural coenzymes, NAD or NADP with their respective thionicotinamide analogues, s-NADP or s-NAD, that have absorbance maxima in reduced forms at 400 nm. 3. 3. s-NAD and s-NADP were found to be good alternate substrates for NAD(P)-dependent malic enzyme, the apparent K m values for the thioderivatives were similar to those of the corresponding natural coenzymes. 4. 4. ATP produced greater inhibition of the NAD or s-NAD linked reactions than of the NADP or s-NADP-linked reactions of skeletal muscle mitochondrial NAD(P)-dependent malic enzyme. 5. 5. At 5 mM malate concentration and in the presence of 2 mM ATP the NADP-linked reaction is favoured and the activity ratios, v ( s- nadp) / v ( nad) or v ( nadp) / v ( s- nad) are 6 and 26, respectively.