Patent ID: 7943337

Claim:
A method of screening a protease for an ability to cleave 1-deoxyfructosyl- L -valyl- L -histidine from a glycated β-chain N-terminal without cleaving a glycated amino acid or a glycated peptide from a glycated α-chain N-terminal of glycated hemoglobin or a fragment thereof, comprising contacting the protease with a hemoglobin α-chain N-terminal glycated peptide having a length of 3 amino acids to 20 amino acids in a first reaction mixture, contacting the protease with a hemoglobin β-chain N-terminal glycated peptide having length of 3 amino acids to 20 amino acids in a second reaction mixture, detecting the glycated amino acid and/or glycated peptide cleaved from the α-chain N-terminal glycated peptide and/or the 1-deoxyfructosyl- L -valyl- L -histidine from the β-chain N-terminal glycated peptide, wherein a protease having an ability to cleave 1-deoxyfructosyl- L -valyl- L -histidine from a glycated β-chain N-terminal without cleaving a glycated amino acid or a glycated peptide from a glycated α-chain N-terminal of glycated hemoglobin can be identified by comparing the relative amounts of the glycated amino acid and/or glycated peptide cleaved from the α-chain N-terminal glycated peptide and the 1-deoxyfructosyl- L -valyl- L -histidine from the β-chain N-terminal glycated peptide.