PEPTIDES OBTAINED BY TRYPTIC HYDROLYSIS OF PERFORMIC ACID-OXIDIZED RIBONUCLEASE

Abstract

In the present study, the chemical structure of ribonuclease has been investigated by the use of trypsin as a reagent. for the hydrolysis of specific peptide bonds in the oxidized protein, and the resulting peptides have been separated and analyzed by ion exchange chromatography. The investigations of Anfinsen, Redfield, Choate, Page, and Carroll (3) have shown that ribonuclease consists of a single peptide chain with the sequence Lys.Glu.Thr.Alaat the amino-terminal end. Amino acid analyses of the chromatographically purified protein (4) have indicated that the chain contains 126 amino acid residues, among which are 8 half cystine residues.’ Since several attempts to confirm the reported (6) presence of sulfhydryl groups in ribonuclease have not been successful (3,7,8), it is assumed, as a working hypothesis, that the single chain is held in a folded form by four disulfide bridges, as postulated by Anfinsen et al. (3). As the first step in the determination of the sequence of amino acids in the A and B chains of insulin, partial hydrolysis by acid was utilized by Sanger and Tuppy and by Sanger and Thompson (9, 10). As Sanger has