The structure of hemopeptide 1–65 from cytochrome c

Hemopeptide 1–65 was cleaved from horse heart cytochrome c by cyanogen bromide and purified by exclusion chromatography. Although the intrinsic viscosity of the hemopeptide is intermediate between that of a compact sphere and a random coil, the ultraviolet circular dichroic spectrum indicates no significant amount of secondary structure. A variety of chemical and spectral measurements indicate that two histidyl residues of the hemopeptide are coordinated with the heme iron, that the indole ring of tryptophan 59 is one-third exposed, that the heme moiety is two-thirds exposed, and that tyrosyl 48 and the third histidyl residue are completely exposed. It was concluded that the hemopeptide has a relatively open conformation quite different from its conformation in the native protein.