Apocytochrome B5 Research Articles

The Amino Acid Sequence of Cytochrome b5

Abstract Calf liver microsomal apocytochrome b5 was hydrolyzed with chymotrypsin and the resulting peptides were resolved on a Dowex 1 column. The isolation and partial amino acid sequences of the 10 chymotryptic peptides are described. The total amino acid composition of these peptides is equal to the sum of the residues present in the tryptic peptides. On the basis of the data obtained for the chymotryptic peptides the order of the tryptic peptides was established. This information, combined with the known sequences of the tryptic peptides, provided sufficient evidence to construct a unique amino acid sequence for the 85 amino acid residues in cytochrome b5.

The Reactivity of the Lysyl Residues of Cytochrome b5

Abstract The modification of α- and e-amino groups in cytochrome b5 with acetic anhydride, succinic anhydride, and 2,4,6-trinitrobenzene 1-sulfonic acid (trinitrobenzene sulfonate) was described. Acylation of these residues increases the rate of heme dissociation from the protein in the presence of urea, without altering the spectrum or enzymatic reduction of the cytochrome. Trinitrophenylation of all of the α- and e-amino groups results in a marked alteration of the protein structure. Even more extensive changes in the protein structure occurred when trinitrophenylation was carried out in the absence of the heme. The kinetics of trinitrophenylation showed that 3 of the lysyl residues in cytochrome b5 are particularly reactive. These residues are largely confined to the heme peptide core rather than to the lysyl residues near the amino- and carboxyl-terminal ends of the protein. Because the completely acetylated apocytochrome b5 recombines with heme to yield a cytochrome b5 with unaltered spectral properties, the α- and the e-amino groups are not involved directly in either heme binding or the catalytic activity of cytochrome b5.

The Interaction of Porphyrins and Metalloporphyrins with Apocytochrome b5

The Interaction of Porphyrins and Metalloporphyrins with Apocytochrome b5