Catalytic subunit of the essential mitochondrial processing protease (MPP), which cleaves the mitochondrial sequence off newly imported precursors proteins (PubMed:2007593, PubMed:9299349, PubMed:9654444). 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 (PubMed:9654444, PubMed:9299349). Inhibited by high levels (> 1uM) of zinc (PubMed:9654444). Inhibited by metal chelators ethylenediaminetetraacetic acid (EDTA) and O-phenanthroline (PubMed:9654444). Heterodimer of MAS2 (alpha) and MAS1 (beta) subunits, forming the mitochondrial processing protease (MPP) in which MAS2 is involved in substrate recognition and binding and MAS1 is the catalytic subunit. Present with 1360 molecules/cell in log phase SD medium. Belongs to the peptidase M16 family.