Identification and characterization of a new tom40 isoform, a central component of mitochondrial outer membrane translocase.

Newly synthesized precursors are transported into mitochondria through an outer membrane translocase, TOM. Tom40, a central pore-forming component, interacts directly with precursors to help them translocate across the outer membrane. We identified a new isoform of rat Tom40, Tom40B, which is conserved among mammals and exhibits significant similarities to Tom40 in other eukaryotes.

Dual subcellular distribution of cytochrome b5 in plant, cauliflower, cells.

Subfractionation studies showed that cytochrome b(5) (cyt b5), which has been considered to be a typical ER protein, was localized in both the endoplasmic reticulum membrane (ER) and the outer membrane of mitochondria in cauliflower (Brassica olracea) cells and was a component of antimycin A-insensitive NADH-cytochrome c reductase system in both membranes. When cDNA for cauliflower cyt b5 was introduced into mammalian (COS-7) and yeast cells as well as into onion cells, the expressed cytochrome was localized both in the ER and mitochondria in those cells. On the other hand, rat and yeast cyt b5s were specifically localized in the ER membranes even in the onion cells.

Integration of cytochrome b5 into endoplasmic reticulum membrane: participation of carboxy-terminal portion of the transmembrane domain.

Integration of cytochrome b(5) (b5), a tail-anchored protein located in the endoplasmic reticulum (ER) membrane, into the membrane was studied. Mutation of three amino acids, -Leu-Met-Tyr, at the carboxy-terminal end of the transmembrane segment of b5 to alanines resulted in localization of the mutated protein, b5LMY/AAA, in the cytosol as well as in the ER membrane. When an N-glycosylation site was introduced at the carboxy-terminal end of b5LMY/AAA, a substantial amount of the glycosylated form of the mutant protein was recovered in the cytosol fraction.

Identification of outer mitochondrial membrane cytochrome b5 as a modulator for androgen synthesis in Leydig cells.

Outer mitochondrial membrane cytochrome b5 is an isoform of microsomal membrane cytochrome b5. In rat testes the outer mitochondrial membrane cytochrome b5 is present in both mitochondria and microsomes, whereas microsomal membrane cytochrome b5 is undetectable. Outer mitochondrial membrane cytochrome b5 present in the testis was localized in Leydig cells with cytochrome P-45017alpha, which catalyzes androgenesis therein.