Skeletal muscle NAD+(P) and NADP+-dependent malic enzyme in Friedreich's ataxia.

Malic enzymes were studied in skeletal muscle from seven patients with Friedreich's ataxia (FA) and nine controls. Muscle contained three different malic enzymes. There were two strictly NADP+-dependent enzymes, one in the cytosol and one in mitochondria. These two enzymes are not allosteric. In FA muscle, activity of the mitochondrial NADP+-linked enzyme was significantly low and the cytosol NADP+-linked enzyme was significantly increased. A third malic enzyme, NAD+(P)-dependent, was found in the mitochondrial fraction. That enzyme had allosteric properties, and its activity was about the same in FA and control muscle.