SEQUENTIAL DEGRADATION OF PEPTIDES WITH AN INSOLUBLE EDMAN REAGENT

An insoluble Edman reagent, analogous to phenyl isothiocyanate, has been synthesized from polystyrene beads (cross-linked with 0.25% divinylbenzene) by nitration, reduction, and reaction with carbon disulfide and ethyl chloroformate. To enable the NCS-polystyrene to swell in polar solvents, it was essential to reduce its hydrophobicity by coupling 60% of the NCS groups to glucosaminol. The resulting resin, which swells extensively both in a solvent containing 20% water, 75% pyridine, and 5% N-ethylmorpholine (used for addition of peptide to resin) and in a mixture of 80% trifluoroacetic acid and 20% acetic acid (used for cleavage), has been used to degrade several peptides sequentially from their amino termini, for a maximum of 10 cycles. Recoveries of degraded peptide average about 75% per stage. This relatively poor recovery is primarily responsible for the current restriction of the method to peptides of moderate size. Degradations have been followed by determining the amino acid composition of the peptide after each cycle. The results are unambiguous even after many cycles have been performed since the terminal amino acid is lost after each degradation. One complete cycle takes about 2 hr and several peptides can be degraded in tandem very easily. © 1969, American Chemical Society. All rights reserved.