Lineweaver-Burk analysis of NO generation by XO as a function of nitrite concentration at different oxygen tensions. Reciprocal plot, 1/velocity versus 1/[nitrite]. A, 0.02 mg/ml XO, 0.02 mM xanthine in the presence of 400 units/ml SOD and 4–60 mM nitrite. B, 0.02 mg/ml XO and 0.5 mM DBA in the presence of 400 units/ml SOD and 2–64 mM nitrite. Oxygen concentrations of 214, 102, 51, and 20 μM, respectively, were achieved with purging of the sample solutions at 37 °C with 21, 10, 5, or 2% oxygen. Reproduced from [18].