Fig. 4.

Human and Rodent RBCs do not demonstrate XO-catalyzed nitrite reductase activity. Human, mouse, and rat samples were analyzed for XOR-dependent contributions to overall NO₂⁻ reductase activity using the Sievers Nitric Oxide Analyzer (NOA) as detailed in the methods. Samples were prepared in the reaction chamber with 50 μL of RBC homogenate (5 mg total protein) in KPi pH 7.0 with or without xanthine (25 μM) and with or without febuxostat (10 μM). Reactions were initiated by the addition of NaNO₂⁻ (500 μM). A) Representative NO generation profiles from human RBC homogenates + xanthine with or without addition of febuxostat (Febux). B) Human, mouse, and rat RBC homogenate values (alone or with xanthine or with xanthine and febuxostat). Authentication of NO was determined by diminution of the signal by the presence of the electron spin resonance NO spin trap carboxy-PTIO. Data represent the mean ± SD of n = 4.