Patent ID: 8658382

Claim:
A method for simultaneous quantitative analysis of both tetrahydrobiopterin and its oxidized forms in a sample, which comprises: (a) adding the sample comprising both tetrahydrobiopterin and its oxidized forms to an enzyme solution comprising (i) a protein having an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4, and 5, and (ii) UDP-glucose or UDP-xylose, and then performing an enzymatic reaction; (b) oxidizing the reaction mixture obtained in Step (a) and then measuring each amount of biopterin and biopterin-glycoside product; and (c) obtaining an amount of tetrahydrobiopterin from the amount of biopterin-glycoside product obtained from Step (b), using a calibration curve between biopterin and biopterin-glycoside product.