Malate transport into heart mitochondria.

The oxidation of l-Malate to carbon dioxide was employed as a measure of malate transport into mitochondria. Conditions of incubation were optimized with regard to osmolarity, pH, phosphate concentration, and substrate concentrations. Under these conditions the rate of malate oxidation to carbon dioxide was 17.1 ± 2.1 μmol/min/g mitochondrial protein at 30°C. Previous workers have found that maximum oxidation of glucose by the isolated perfused rat heart is from 2.4 to 3.0 μmol/min/g dry weight of tissue which would require the transport of 22 to 28 μmol of malate/min/g mitochondrial protein. Since the perfused heart experiments were carried out at 37°C, it is apparent that malate transport into mitochondria can account for most, if not all, of the reducing equivalents generated during glycolysis.