This subfamily contains peptidase M48C Oma1 (also called mitochondrial metalloendopeptidase OMA1) protease homologs that are mostly uncharacterized. Oma1 is part of the quality control system in the inner membrane of mitochondria, with its catalytic site facing the matrix space. It cleaves and thereby promotes the turnover of mistranslated or misfolded membrane proteins. Oma1 can cleave the misfolded multi-pass membrane protein Oxa1, thus exerting a function similar to the ATP-dependent m-AAA protease for quality control of inner membrane proteins; it cleaves a misfolded polytopic membrane protein at multiple sites. It has been proposed that in the absence of m-AAA protease, proteolysis of Oxa1 is mediated by Oma1 in an ATP-independent manner. Oma1 is part of highly conserved mitochondrial metallopeptidases, with homologs present in higher eukaryotes, eubacteria and archaebacteria, all containing the zinc binding motif (HEXXH). It forms a high molecular mass complex in the inner membrane, possibly a homo-hexamer.