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). Required for PINK1 turnover by coupling PINK1 mitochondrial import and cleavage, which results in subsequent PINK1 proteolysis (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 PMPCA is required for catalytic activity. Heterodimer of PMPCA (alpha) and PMPCB (beta) subunits, forming the mitochondrial processing protease (MPP) in which PMPCA is involved in substrate recognition and binding and PMPCB is the catalytic subunit. Belongs to the peptidase M16 family.