Abstract: The present invention is to provide a method for easily and specifically modifying specific amino acid residue(s) constituting a peptide and to provide a methodology of improving the accuracy of identification of the peptide using a new information of the peptide obtained from the number of modified amino acid residue by said specific modification method as mentioned. The method for modifying a peptide according to the present invention is characterized: A method for modifying a peptide, wherein the peptide as supported in a substrate and an aqueous solution of perhalogenated carboxylic acid containing an alcohol is reacted to selectively esterify a glutamic acid residue of said peptide.

Abstract: The present invention is to provide a method for cleavage of peptidic bond at C terminal of peptide and a method for determination of C terminal amino acid sequence of peptide without the decrease of the sensitivity and with preventing the subsidiary reaction. The method for cleavage of peptidic bond at C terminal of peptide according to the present invention is characterized as follows: A method for cleavage of peptidic bond at C terminal of peptide comprising the steps of: reacting a peptide with a solution of perhalogenated carboxylic acid containing alcohol to esterify glutamic acid residue of said peptide; and reacting said peptide with alkanoic acid anhydride to obtain C terminal-deleted peptide in which the amino acid residue of said peptide at C terminal is sequentially deleted.