Patent ID: 7579165

Claim:
A method for derivatizing a protein or peptide to a sulfonic acid derivative, comprising steps of: modifying a N-terminus in a protein or peptide with an immobilized compound A bound to a solid support to obtain a protein or peptide modified with the immobilized compound A at the N-terminus, said immobilized compound A comprising a disulfide group and a functional group which reacts with the N-terminus in the protein or peptide; fragmenting the obtained protein or peptide modified with the immobilized compound A into a N-terminal peptide fragment comprising the immobilized compound A and containing a disulfide bond, and one or more peptide fragments other than said N-terminal peptide fragment; separating the N-terminal peptide fragment from the other peptide fragments to selectively collect the N-terminal peptide fragment; and cleaving the disulfide bond of the disulfide group to convert into a sulfonic acid group, thereby converting the modified protein or peptide into a sulfonic acid derivative, wherein said immobilized compound A is selected from the group consisting of 3-([2-aminoethyl]dithio)propionic acid hydrochloride (AEDP), cystine, AEDP in which the carboxyl group of AEDP is replaced by an isothiocyanate or active ester, and cystine in which the carboxyl group of cystine is replaced by an isothiocyanate or active ester, and wherein in the cleaving step, the disulfide bond in the N-terminal peptide fragment that originates from the immobilized compound A is cleaved and converted into the sulfonic acid group and thereby the derivatized N-terminal peptide fragment is obtained.