Complex formation between methionine and a heme peptide from cytochrome c.

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Abstract
N-Acetyl-DL-methionine, N-acetyl-DL-methionlne methyl ester, diethyl sulfide, and several other thioethers have been shown to form complexes with a heme octapeptide from horse heart cytochrome c, with a glutathione adduct of iron protoporphyrin IX, and, in a few instances tested, with iron protoporphyrin K itself. Binding in the peptide systems occurs to the lower limit of the pH-range covered (pH2), is stronger in the reduced than in the oxidized state, and results in the appearance of hemochrome- and hemichrome-type spectra. The oxidation-reduction potential of the heme octapeptide in the presence of N-acetyl-DL-methionine is less negative than that of the imidazole-heme octapeptide system at pH 7. The possiblity is considered that methionine-heme binding might occur among the cytochromes c.