Has a dual role in the assembly of mitochondrial ATPase. Acts as a protease that removes the N-terminal 10 residues of mitochondrial ATPase CF(0) subunit 6 (ATP6) at the intermembrane space side. Also involved in the correct assembly of the membrane-embedded ATPase CF(0) particle, probably mediating association of ATP6 with the subunit 9 ring. Interacts with ATP6. Associates loosely with the inner membrane. Belongs to the peptidase M76 family. Extended N-terminus. Extended N-terminus.