Mammalian mitochondrial and microsomal cytochromes b5 exhibit divergent structural and biophysical characteristics

Document Type


Publication Date



The only outer mitochondrial membrane cytochrome b5 examined to date, from rat (rOM b5), exhibits greater stability than known mammalian microsomal (Mc) isoforms, as well as a much higher kinetic barrier for hemin dissociation and a more negative reduction potential. A BlastP search of available databases using the protein sequence of rOM b5 as template revealed entries for analogous proteins from human (hOM b5) and mouse (mOM b5). We prepared a synthetic gene coding for the heme-binding domain of hOM b5, and expressed the protein to high levels. The hOM protein exhibits stability, hemin-binding, and redox properties similar to those of rOM b5, suggesting that they are characteristic of the OM b5 subfamily. The divergence in properties between the OM and Mc b5 isoforms in mammals can be attributed, at least in part, to the presence of two extended hydrophobic patches in the former. The biophysical properties characteristic of the OM proteins may be important in facilitating the two functions proposed for them so far, reduction of ascorbate radical and stimulation of androgen synthesis. © 2003 Elsevier Inc. All rights reserved.

Publication Source (Journal or Book title)

Biochemical and Biophysical Research Communications

First Page


Last Page


This document is currently not available here.