The Complete Amino‐Acid Sequence of the Low‐Spin Class II Cytochrome c‐556 from Agrobacterium tumefaciens Strain B2a

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Abstract
The amino acid sequence of the soluble monoheme cytochrome c-556 from A. tumefaciens, strain B2a, was determined. The sequence was derived from peptides obtained by digestion of the apoprotein with trypsin and chymotrypsin, and by subdigestion of some of the peptides with Staphylococcus aureus protease and thermolysin. Sequencing of the various peptides was achieved by a combination of manual dansyl-Edman degradation and automatic liquid-phase sequence analysis. The main characteristic of this cytochrome is that the heme-binding sequence Cys-Xaa-Yaa-Cys-His occurs in the C-terminal region of the polypeptide chain, the first cysteine being located 11 residues ahead of the C-terminal lysine-122. The protein belongs to cytochrome c sequence class II. The cytochrome c-556 is the first example known of a class II cytochrome of the low-spin type isolated from an obligate aerobic organism.