| abstract |
(57) [Problem] To provide a method of isotopically labeling a functional group of an amino acid residue of a protein, and to provide a protein in which the functional group of an amino acid residue is isotopically labeled. SOLUTION: An enzyme replaces a functional group of an amino acid residue of a protein with an isotope-labeled group derived from an isotope-labeled compound. In particular, transglutaminase is allowed to act on a glutamine residue of a protein in the presence of an isotope-labeled compound, and the carboxyamide nitrogen of the glutamine residue is replaced with an isotope-labeled group. |