[35] Solid-phase COOH-terminal sequential degradation

Publisher Summary A method of peptide sequencing from the COOH terminus, using a chemical method, was introduced recently. One procedure described in the chapter is to couple the peptide with S-n-butyl thiuronium iodide with dicyclohexylcarbodiimide by heating at 50 ° for 10-15 min. Cleavage was effected with aqueous base at pH 10-11.5. One other chemical sequencing method was reported in detail by Stark. In this method, protein and peptidyl thiohydantoins were prepared and sequentially cleaved with the release of the amino acid, thiohydantoin, from the carboxyl terminus. Three cycles of degradation were usually satisfactory. The Stark method in free solution was studied with the objective of improving on the yields previously reported, but with little success. At the fourth cycle of degradation, the yield dropped dramatically to about 10%. The use of solid-phase sequencing, in conjunction with the Stark method, offers advantages for removing both excess reagents and thiohydantoin from the residual attached peptide.