Isolation and characterization of human liver cytochrome b5 cDNA

Three cDNA clones encoding human cytochrome b5 have been isolated and sequenced from a lambda gt 11 cDNA library of a human liver. The largest clone (b5-C) contains 765 base pairs corresponding to a complete coding sequence of 134 amino acids and sequences for 5' non-coding (56 bases) and 3' non-coding regions (307 bases). In Northern blots, a band hybridizing to 32P-labelled b5-B cDNA clone was detected at around 12S in mRNA of human and rat livers. The deduced amino acid sequence was identical with the partial amino acid sequence (2-100th) previously reported, except that two amino acid replacements were observed between the 89th and 91st positions. The deduced amino acid sequence of human cytochrome b5 shares 88.0, 86.5, 86.5 and 74.4% similarity with those of rat, pig, horse and chicken, respectively. The sequences in the haem binding region were highly conserved among these species. In addition, high similarities in the hydrophobicity profiles were maintained throughout their entire regions, although some diversity was observed in the N-terminal sequences between human and chicken.