Neurospora crassa cytochrome c. II. Chymotryptic peptides, tryptic peptides, cyanogen bromide peptides, and the complete amino acid sequence.

The complete amino acid sequence of Neurospora crassa cytochrome c has been determined. The molecule consists of a single polypeptide chain containing 107 residues. The NH2-terminal residue is glycine, and the COOH-terminal residue is alanine. There are 39 amino acid differences between the cytochromes of N. crassa and those of the yeast Saccharomyces cerevisiae, whereas there are 43 amino acid differences between the cytochromes c of Neurospora and human heart. For all of the presently known cytochromes c, the number of amino acids which occupy the same position is reduced to 39. N. crassa cytochrome c has only 2 histidine residues in positions 18 and 33, whereas tuna fish cytochrome has 2 histidine residues in positions 18 and 26. It is suggested that the histidine residue in position 18 contributes the fifth ligand to the heme iron, and that the sixth ligand in cytochrome c is not formed with histidine or with another nitrogenous group, but with an unknown ligand.