Studies on sequencing of peptides from the carboxyl terminus by using the thiocyanate method

We report on our experience in applying the thiocyanate method developed by Stark (1968) (Biochemistry 7, 1796-1807) to the sequencing of short peptides from the carboxyl end in free solution. Yields fell to very low levels after three cycles of degradation. The method was time-consuming because of the filtration and freeze-drying stages involved. To overcome these problems, peptides were attached to modified polystyrene polymers for sequential degradation in the solid phase, and a maximum of six amino acids was determined. Also, ribonuclease was attached to active-ester glass beads and sequential degradation was carried out to determine six amino acids at the C-terminal end of this protein.