Functional characterization of human xanthine oxidase allelic variants

Objective Xanthine oxidase (XO) catalyzes the oxidation of endogenous and exogenous purines and pyrimidines. In this study, we speculated that individual variations in XO activity are caused by genetic variations in the XO gene. Methods To investigate the genetic variations in XO in 96 Japanese participants, denaturing high-performance liquid chromatography was used. To assess the effects of these variations on enzymatic activity, wild-type XO and 21 types of variant XO - including those in the database and those just discovered - were transiently expressed in COS-7 cells. Results Three nonsynonymous single nucleotide polymorphisms, including 514G>A (Gly172Arg), 3326A>C (Asp1109Thr), and 3662A>G (His1221Arg) were identified in Japanese participants. Functional characterization of 21 XO variants showed a deficiency in enzyme activity in two variants (Arg149Cys and Thr910Lys); low activity (intrinsic clearance, CUM: 22-69% compared with the wild-type) in six variants (Pro555Ser, Arg607Gln, Thr62311e, Asn909Lys, Pro1150Arg, and Cys1318Tyr); and high activity (CLint: approximately two-fold higher than that in the wild-type) in two variants (IIe703Val and His1221Arg). Conclusion These results suggest that several single nucleotide polymorphisms in the XO gene are involved in individual variations in XO activity. In addition, such findings will be useful to identify xanthinuria patients.