Cytochrome b5 Reductase 4 (CYB5R4)

By searching EST databases for consensus NADPH- and flavin-binding sites, followed by RT-PCR of a hepatoma cell line cDNA library, Zhu et al. (1999) cloned NCB5OR, which they designated 'B5+B5R.' The deduced 487-amino acid protein contains 2 N-terminal heme-binding domains characteristic of CYB5, followed by a 100-amino acid hinge region and a CYB5 reductase domain, which includes 2 FAD-binding motifs and 3 C-terminal NADPH-binding motifs.

Unlike CYB5 and DIA1, NCB5OR has no membrane anchor. Northern blot analysis detected a 2.4-kb transcript in all tissues and cell lines examined. Confocal microscopy of epitope-tagged NCB5OR revealed a perinuclear distribution following expression in COS-7 cells.