Protease that is part of the quality control system in the inner membrane of mitochondria (PubMed:12963738, PubMed:22219186, PubMed:24648523, PubMed:27325672). Activated in response to various mitochondrial stress, leading to the proteolytic cleavage of target proteins, such as OXA1 and COX1 (PubMed:12963738, PubMed:22219186, PubMed:24648523). Cleaves and thereby promotes the turnover of mistranslated or misfolded membrane proteins (PubMed:12963738, PubMed:27325672). Cleaves the misfolded multi-pass membrane protein OXA1 (PubMed:12963738). Involved in quality control of cytochrome oxidase assembly: mediates the cleavage of COX1 in cells lacking COA2 (PubMed:22219186). Required for the stability of the respiratory supercomplexes (PubMed:26365306). Required for TOR signaling (PubMed:27325672). Binds 1 zinc ion per subunit. Protease activity is induced in response to various mitochondrial stress, such as changes in membrane potential, oxidative stress or chronic hyperpolarization, and depends on its C-terminal region. Homooligomer. Forms a redox-dependent disulfide bond, which plays a structural role and regulates its conformational stability and activity. Reduced ability to form viable colonies on glucose medium after acute treatment with hydrogen peroxide or chronic exposure to carbonyl cyanide m-chlorophenylhydrazone (CCCP) (PubMed:24648523). Cells are resistant to rapamycin and display reduced TOR signaling (PubMed:27325672). Oxidative-stress response is impaired (PubMed:27325672). Belongs to the peptidase M48 family.