THE CYTOCHROME-C REDUCTASE INTEGRATED PROCESSING PEPTIDASE FROM POTATO MITOCHONDRIA BELONGS TO A NEW CLASS OF METALLOENDOPROTEASES

The general mitochondrial processing peptidase that removes the N-terminal targeting signals from proteins imported into mitochondria forms part of a respiratory protein complex in potato (Solanum tuberosum L.). We have termed this complex the ''cytochrome c reductase/processing peptidase complex'' and show that it acts on a variety of precursor proteins from different intramitochondrial locations. In potato, biochemical methods fail to separate the ubiquinol cytochrome c oxidoreductase function from the function of the processing protease. On the other hand, inhibition of electron flow with antimycin A or myxothiazol does not affect processing activity. The integration into an oligomeric protein complex causes the unique properties of the processing enzyme. It is fully active at high pH and in the presence of high salt. It does not need externally added metal ions, but it is inhibited by EDTA and 1,10-phenanthroline. Other protease inhibitors have no effect on the processing activity. Taken together, the molecular genetic and physiological results indicate that the mitochondrial processing protease does not belong to the thermolysin superfamily of metalloproteinases but may be a member of a new class of metalloendoproteases.