Amino acid sequence of rattlesnake heart cytochrome c.

Since the complete amino acid sequence of horse heart cytochrome c was first reported (l), the sequences of additional cytochromes c from other species have been studied (see reviews by Smith and Margoliash (2) and by Margoliash and Smith (3)). These studies have provided considerable information which is of interest from the viewpoint of structure-function relationships in these homologous proteins. Such comparative sequence studies also provide an opportunity to consider the evolution of this protein, since all of the cytochromes c of higher organisms are presumably the product of a single gene which has become modified during the long period of the development of aerobic species. For these reasons, it was of interest to examine the amino acid sequence of the cytochrome c of a reptile, and we report here studies on the protein isolated from hearts of the eastern diamondback rattlesnake, Crotalus aclamanteus.1 Because only limited amounts of the pure protein were available, less than 10 pmoles, investigations were confined to a brief study of physical homogeneity to be certain of purity and similarity to other vertebrate cytochromes, to an examination of the amino acid composition, and to the isolation and determination of the sequences of peptides from a chymotryptic digest. By analogy with other cytochromes, it was possible to deduce the complete sequence of the protein.