The present invention provides a protein comprising an amino acid sequence in which arginine at position 61 of a protein comprising the amino acid sequence represented by SEQ ID NO: 1 is substituted to an amino acid selected from the group consisting of glycine, alanine, valine, leucine, serine, threonine, proline, cysteine, methionine, asparagine, glutamine, and aspartic acid; and a method for measuring a glycated hemoglobin in a sample, wherein the method comprises reacting a glycated hemoglobin in a sample with a protease to produce a glycated hexapeptide, then reacting the produced glycated hexapeptide with the aforementioned protein, and measuring a substance produced or consumed by the reaction.