We here describe in detail our method whereby the carboxyl-terminal residue of a peptide may be determined. The procedure involves, first, formation of an 0-substituted hydroxamic acid by reaction of the peptide C-terminal carboxyl group with a water-soluble carbodiimide and a nucleophilic 0-substituted hydroxylamine. Considerations leading to the choice of 0- pivaloylhydroxylamine (10, OPHA) as the nucleophile are described, and optimization of ...