Primary structure of yeast cytochrome c peroxidase : I. Chemical characterization of the polypeptide chain and of tryptic and chymotryptic peptides

Abstract

The amino acid composition of yeast cytochrome c peroxidase was determined and calculated assuming that the enzyme contained one protoheme per molecule. On the basis of the amino acid composition and heme content the minimum M r was calculated to be 35,235. Gel electrophoresis in the presence of sodium dodecyl sulfate indicated the presence of a single polypeptide chain with a M r of approximately 33,000. A single cysteinyl residue present in the molecule was shown to be resistant against reaction with iodoacetic acid in the native form of both holo- and apo-enzymes, but readily modified with the reagent in the denatured form. Automated Edman degradation yielded an aminoterminal sequence of 11 residues beginning with threonine. Twenty-eight tryptic and 47 chymotryptic peptides were isolated from the carboxymethylated apoprotein and subjected to the sequence analysis by the dansyl-Edman method. The results with these peptides confirmed and extended the amino- and carboxyl-terminal sequences and in addition provided a partial sequence covering approximately 90% of the polypeptide chain.