The generation of superoxide anion in the reaction of tetrahydropteridines with molecular oxygen

Abstract

The reduction rates of nitro blue tetrazolium with 2-amino-4-hydroxy-6,7-dimethyl-4,5,6,7-tetrahydropteridine, tetrahydrobiopterin, and tetrahydrofolate under aerobic conditions at pH 7.4 at 25 °C were negligible, but were accelerated in the presence of Triton X-100 above its critical micelle concentration. These reactions were substantially inhibited by superoxide dismutase, indicating the participation of O 2 −, generated in the reaction system, in the reduction of nitro blue tetrazolium. At pH 8.5, O 2 −-dependent reduction of nitro blue tetrazolium with the tetrahydropteridines occurred in the absence of Triton X-100. The autoxidation of the tetrahydropteridines was also substantially inhibited by superoxide dismutase. This indicates that O 2 − plays an important role in the overall process of tetrahydropteridine oxidation by O 2. It is suggested from these results that tetrahydropteridines generate O 2 − in vivo in their reaction with O 2.