Mitochondrial malic enzyme from crustacean and fish muscle.

1. In contrast to mammalian skeletal muscle mitochondria, the only substrate that crustacean and fish mitochondria oxidize at a high rate is malate. 2. The mitochondria isolated from muscles of fish and crayfish exhibit a high activity of malic enzyme. 3. Assuming that malic enzyme is responsible for the conversion of malate to pyruvate in animal muscle, it could be expected that the mitochondria which possess high activity of this enzyme should oxidize malate very rapidly when oxygen is available. 4. Some properties of different molecular forms of malic enzyme are reviewed.