Catalytic subunit of the essential mitochondrial processing protease (MPP), which cleaves the mitochondrial sequence off newly imported precursors proteins (By similarity). Preferentially, cleaves after an arginine at position P2 (By similarity). Release of N-terminal transit peptides from precursor proteins imported into the mitochondrion, typically with Arg in position P2. Binds 1 zinc ion per subunit. Binding to mas2 is required for catalytic activity. Heterodimer of mas2 (alpha) and qcr1 (beta) subunits, forming the mitochondrial processing protease (MPP) in which mas2 is involved in substrate recognition and binding and qcr1 is the catalytic subunit. Belongs to the peptidase M16 family.