Potential channel-forming protein implicated in import of protein precursors into mitochondria. Forms part of the preprotein translocase of the outer mitochondrial membrane (TOM complex) containing TOMM22, TOMM40, TOMM40L and TOMM70. Interacts with mitochondrial targeting sequences. Widely expressed. Higher levels in heart, brain and liver, very low level in testis. Belongs to the Tom40 family.