Mitochondrial inner membrane protease ATP23 has two roles in the assembly of mitochondrial ATPase. Firstly, it acts as a protease that removes the N-terminal 10 residues of mitochondrial ATPase CF(0) subunit 6 (ATP6) at the intermembrane space side. Secondly, it is involved in the correct assembly of the membrane-embedded ATPase CF(0) particle, probably mediating association of ATP6 with the subunit 9 ring [, ].