Metalloprotease that is part of the quality control system in the inner membrane of mitochondria. Activated in response to various mitochondrial stress, leading to the proteolytic cleavage of target proteins, such as opa1 and dele1. Following stress conditions that induce loss of mitochondrial membrane potential, mediates cleavage of opa1 at S1 position, leading to opa1 inactivation and negative regulation of mitochondrial fusion (By similarity). Also acts as an activator of the integrated stress response (ISR): in response to mitochondrial stress, mediates cleavage of dele1 to generate the processed form of dele1 (S-DELE1), which translocates to the cytosol and activates eif2ak1/hri to trigger the ISR (By similarity). Required for the stability of the respiratory supercomplexes (PubMed:26365306). Binds 1 zinc ion per subunit. Protease activity is activated upon autocatalytic cleavage in response to mitochondrial depolarization. Homooligomer. The stress-sensor region regulates proteolysis and activation. Autocatalytically cleaved in response to mitochondrial depolarization both at the N-terminus and C-terminus to generate the short active form (S-OMA1). The S-OMA1 form is unstable. May form a redox-dependent disulfide bond (By similarity). Exists in a semi-oxidized state and is activated by prolonged hypoxia (By similarity). Morpholino knockdown of the protein causes developmental defects, such as pericardial edema, smaller eyes and shorter body length (PubMed:26365306). Bioenergetics defects are observed in dells (PubMed:26365306). Belongs to the peptidase M48 family.