The function of MTCH1 (mitochondrial carrier 1, ENSG00000137409) is as follows. Protein insertase that mediates insertion of transmembrane proteins into the mitochondrial outer membrane (PubMed:36264797). Catalyzes insertion of proteins with alpha-helical transmembrane regions, such as signal-anchored, tail-anchored and multi-pass membrane proteins (By similarity). Does not mediate insertion of beta-barrel transmembrane proteins (By similarity). May play a role in apoptosis (PubMed:12377771). {ECO:0000250|UniProtKB:Q9Y6C9, ECO:0000269|PubMed:12377771, ECO:0000269|PubMed:36264797}.