Evidence for intra-mitochondrial degradation of the extrapeptide of ornithine aminotransferase.

When rat liver mitochondria that had imported a synthetic extrapeptide of ornithine aminotransferase (composed of 34 amino acids) were incubated at 25 degrees C, the extrapeptide in their matrix was degraded inside the mitochondria. The degradation of the extrapeptide did not depend on energy either inside or outside the mitochondria. The degrading activity was found exclusively in the mitochondrial soluble fraction and only inhibited by N-ethylmaleimide of eight protease-inhibitors tested. These observations show that the extrapeptide cleaved from the precursor of the mitochondrial protein in the mitochondria is degraded by some ATP-independent proteases inside the mitochondria.