The Amino Acid Sequence of Ovine Pancreatic Ribonuclease A

The amino acid sequence of ovine pancreatic ribonuclease has been derived by the fragment approach. The reduced, S-aminoethylated protein was subjected to tryptic hydrolysis. Peptides derived from all segments of the 124-residue chain were isolated, and their amino acid sequences determined by conventional methods. Alignment of the peptides proceeded from close homology with the amino acid sequence of the bovine enzyme. The ovine enzyme shows the following replacements: serine for threonine at position 3; serine for alanine at position 19; glutamine for lysine at position 37; and glutamine for asparagine at position 103. The results, together with the known amino acid sequences for the enzymes from the cow, pig, and rat, provide an increasingly detailed impression of the species variability of this protein and indicate that pancreatic ribonuclease is an enzyme which is undergoing evolution relatively rapidly in comparison to cytochrome c.