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-term inal 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 pr oteins from different intramitochondrial locations. In potato, biochem ical methods fail to separate the ubiquinol cytochrome c oxidoreductas e 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 pr otein complex causes the unique properties of the processing enzyme. I t 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 physiol ogical results indicate that the mitochondrial processing protease doe s not belong to the thermolysin superfamily of metalloproteinases but may be a member of a new class of metalloendoproteases.