Intramitochondrial intermembranal reversible translocation of aspartate aminotransferase and malate dehydrogenase through the inner mitochondrial membrane.

The translocation of aspartate aminotransferase, malate dehydrogenase, and bulk protein from the rat liver inner mitochondrial membrane and matrix toward the intermembranal space induced by certain organic acids (movement effectors) has been studied. Experiments involving a two-stage dissolution of the mitochondrial membranes by the use of detergents strongly suggest that enzymes like aspartate amino-transferase can cross the inner mitochondrial membrane providing exogenous movement effector was present. Experiments which measured the changes in membranal distribution of malate dehydrogenase induced by the movement effectors also suggested the occurrence of a similar phenomenon for this enzyme in intact mitochondria. Control experiments revealed that under our experimental conditions, the inner mitochondrial membrane remained impermeable to small molecules, e.g., sucrose, and that the release of aspartate aminotransferease, malate dehydrogenase, insocitrate dehydrogenase, and bulk protein into the intermembranal space in the presence of succinate occurred at a much lower concentration of digitonin than that required to disrupt the inner mitochondrial membrane.