Evidence that two forms of bovine erythrocyte cytochrome b5 are identical to segments of microsomal cytochrome b5.

Abstract

Homogeneous preparations of 2 forms of soluble cytochrome b5 were obtained from bovine erythrocytes by successive chromatography on DEAE-cellulose, Bio-Gel P-60 and DEAE-Sephadex. Although the 2 forms could be separated on disc gel electrophoresis, they appeared to have similar MW of approximately 12,000 and identical visible absorbance spectra. The tryptic hemepeptides derived from the 2 forms of bovine erythrocyte cytochrome b5 are electrophoretically indistinguishable from each other and from the tryptic core hemepeptide derived from liver microsomal cytochrome b5. The bovine erythrocyte tryptic hemepeptide was purified to homogeneity; its amino acid composition was identical to that of tryptic hemepeptide from liver microsomal cytochrome b5. The amino acid compositions of the 2 isolatable forms of erythrocyte cytochrome b5 correspond well to the compositions of the 97- and 95-residue segments of native liver microsomal cytochrome b5 that begin at the NH2 terminus. Soluble erythrocyte cytochrome b5 seem to be derived from microsomal protein by proteolysis during erythroid maturation.