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. Author manuscript; available in PMC: 2012 Jul 1.
Published in final edited form as: Free Radic Biol Med. 2011 Apr 15;51(1):179–184. doi: 10.1016/j.freeradbiomed.2011.04.004

Fig. 2. Febuxostat is more potent than allopurinol at inhibiting XO free in solution.

Fig. 2

(A) Xanthine oxidase (2 mU/ml, 5 mM KPi, pH 7.4) was exposed to various concentrations of either allopurinol or febuxostat and assessed for formation uric acid (λ = 295 nm) upon the addition of xanthine (50 μM). Shown are the initial reaction rates (V0) plotted as % control (no inhibitor). IC50 values were calculated as the ordinate value of 50% inhibition (allopurinol = 2.9 μM and febuxostat = 1.8 nM). (B) Same as A except O2 •- formation was detected by the reduction of cytochrome c (λ = 550) and IC50 values were 3.9 μM for allopurinol and 0.9 nM for febuxostat.