The tryptic digestion of S-aminoethylated ribonuclease.

The peptides produced by the tryptic digestion of S-aminoethylated bovine pancreatic ribonuclease support the generally accepted amino acid sequence for this enzyme and also demonstrate the usefulness as well as some special limitations of the aminoethylation procedure. The relative extents of hydrolysis at different peptide bonds were estimated from the yields of purified peptides. Under the conditions used here for tryptic hydrolysis the approximate cleavage of arginyl and lysyl bonds was estimated at 83%, while the corresponding cleavage of aminoethylcysteinyl bonds averaged 56%. Exceptions to these generalizations included the very limited cleavage of lysyl and aminoethylcysteinyl bonds which were adjacent to other basic amino acid residues, and, of course, the negligible splitting of the lysyl proline bond and the ammo-terminal lysyl glutamic acid bond. The extent of cleavage at aminoethylcysteinyl bonds appeared to show greater variability than that at lysyl and arginyl bonds.