Identity of the Heme-Not-Containing Protein in Bovine Heart Cytochrome c₁ Preparation with the Protein Mediating c₁-c Complex Formation-A Protein with High Glutamic Acid Content

Abstract

A heme-not-containing protein was isolated from cytochrome c₁ preparation by gel filtration after carboxymethylation and citraconylation. The amino acid sequence of this protein was determined by the analyses of tryptic and chymotryptic peptides as well as by solid-phase sequence analysis. It consisted of 78 amino acid residues and the molecular weight was calculated to be 9, 175. This protein contained a high proportion of glutamic acid and glutamine (27% of the total residues) but no methionine, isoleucine, tyrosine, and tryptophan. The most notable feature was an acidic cluster of 8 consecutive glutamic acid residues near the amino (N)-terminus. The secondary structure was predicted to have a high proportion of helical content.
The amino acid composition and N-terminal sequence of a protein independently prepared from bovine heart mitochondria, which is essential to the formation of the cytochrome c₁-c complex, suggested that this colorless factor and the present heme-not-containing protein are identical. Evidence shows that another protein, called the non-heme protein, isolated from “two-band” cytochrome c₁ preparation is also the same protein as that presented in this paper.