Channel-forming protein essential for import of protein precursors into mitochondria. Plays a role in the assembly of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) by forming a complex with BCAP31 and mediating the translocation of Complex I components from the cytosol to the mitochondria. Forms part of the preprotein translocase complex of the outer mitochondrial membrane (TOM complex) which consists of at least 7 different proteins (TOMM5, TOMM6, TOMM7, TOMM20, TOMM22, TOMM40 and TOMM70). Interacts with mitochondrial targeting sequences. Interacts with TIMM29; linking the TIM22 complex to the TOM complex. Forms a complex with BCAP31 (via C-terminus) which mediates the translocation of components of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) from the cytosol to the mitochondria (By similarity). Interacts (via N-terminus) with CYP1A1 (via mitochondrial targeting signal); this interaction is required for CYP1A1 translocation across the mitochondrial outer membrane (By similarity). Associates with the mitochondria-associated ER membrane via interaction with BCAP31. Belongs to the Tom40 family.