Purification and characterization of a processing protease from rat liver mitochondria

A processing protease has been purified from the matrix fraction of rat liver mitochondria. The purified protease contained two protein subunits of 55 kd (P‐55) and 52 kd (P‐52) as determined by SDS‐PAGE. The processing protease was estimated to be 105 kd in gel filtration, indicating that the two protein subunits form a heterodimeric complex. At high ionic conditions, the two subunits dissociated. The purified processing protease cleaved several mitochondrial protein precursors destined to different mitochondrial compartments, including adrenodoxin, malate dehydrogenase, P‐450(SCC) and P‐450(11 beta), but the processing efficiencies were different each other. The endoprotease nature of the processing protease was confirmed with the purified enzyme using adrenodoxin precursor as the substrate; both the mature form and the extension peptide were detected after the processing. The processing activity of the protease was inhibited by metal chelators, and reactivated by Mn2+, indicating that the protease is a metalloprotease.