Use of thiocyanic acid to form 2-thiohydantoins at the carboxyl terminus of proteins.

The chemistry of the formation of 2-thiohydantoins on the carboxyl terminal of peptides or proteins was investigated. It was found that thiocyanic acid was much more reactive for the formation of 2-thiohydantoins than were the thiocyanate salts. The physical reasons for this observation are explained. The kinetics of the reaction of a number of proteins, and some of their fragments, with thiocyanic acid were also determined. Simple and safe procedures for the preparation of anhydrous thiocyanic acid solutions were devised. The prospective application of these procedures to sequencing from the carboxyl terminal of a polypeptide is discussed.