Human Cytochrome B5 Research Articles

Structural Studies of Cytochrome bs<subtitle>III. Sequential Studies on Human Liver Cytochrome <italic>b</italic><sub>5</sub></subtitle>

Human liver cytochrome b5 was de-hemed and digested with trypsin [EC 3.4.4.4] at pH 8.0. The digests were separated into a precipitate and a soluble fraction. One peptide was isolated from the precipitate and 8 peptides from the soluble fraction. The 9 peptides were sequenced by Edman degradation, carboxypeptidases [EC 3.4.2.1 and 3.4.2.2] and other digestion methods. On the basis of the results, all of the peptides were aligned by analogy to the known sequence of the closely similar rabbit liver cytochrome bs to give a tentative structure.

Amino Acid Sequences of Tryptic Peptides of Cytochromes b5 from Microsomes of Human, Monkey, Porcine, and Chicken Liver

Abstract Liver microsomal apocytochromes b5 from man, monkey (Alouatta fusca), pig, and chicken were subjected to trypsin digestion, and all of the peptides were isolated and characterized. The sum of the residues present in these peptides equaled the total amino acid composition of the corresponding parent cytochrome. For all of these peptides a homologous segment was found in our previously established bovine and rabbit cytochrome sequence. This information provided sufficient evidence to construct a unique amino acid sequence for human, monkey, porcine, and chicken cytochrome b5. Comparison of the six sequences indicated a close similarity between these proteins. The human cytochrome differed from that of chicken in 15 positions but from that of monkey in only 2 positions. With the exception of the avian protein sequence, the amino acid replacements were confined predominantly to the NH2- and COOH-terminal segments of the cytochrome. A segment comprising residues 42 to 72 was invariant in all six cytochromes.