Purification and structural studies of rabbit erythrocyte cytochrome b5

Abstract

SummaryA single form of cytochrome b5 has been isolated in highly purified form from the cytosolic fraction of rabbit erythrocytes by sequential chromatography on DE-52 cellulose, Sephadex G-75, and DEAE-Sephadex A50. The cytochrome is structurally similar to the N-terminal, heme-binding domain of rabbit liver microsomal cytochrome b5. Like the liver protein, it is blocked at the amino terminus. Its amino acid composition is similar to that of residues 1-97 of the microsomal protein. With one exception, tryptic peptides derived from apo-cytochrome b5 of rabbit erythrocytes co-elute with the tryptic peptides obtained from a soluble hemepeptide fragment of microsomal cytochrome b5. These findings, together with amino acid sequence analysis of the carboxyl terminal tryptic peptides, identify the erythrocyte cytochrome b5 as a 97-residue peptide.