The function of Ensembl gene identifier ENSG00000075336 (TIMM21, translocase of inner mitochondrial membrane 21) is as follows. Participates in the translocation of transit peptide- containing proteins across the mitochondrial inner membrane. Also required for assembly of mitochondrial respiratory chain complex I and complex IV as component of the MITRAC (mitochondrial translation regulation assembly intermediate of cytochrome c oxidase complex) complex. Probably shuttles between the presequence translocase and respiratory-chain assembly intermediates in a process that promotes incorporation of early nuclear-encoded subunits into these complexes. .