Figure 4.

Control experiments investigating possible direct NO and NO₂^– scavenging activity as well as nitrate oxidation by catalase.

(A) NO production was measured as the concentration of nitrite present in the media after 1 h of incubation of the catalase with 5 mM sodium nitroprusside (SNP) at 50°C. Data points were expressed as % of control and represent the mean of four replicates. (B) The concentration of nitrite present in the media after 1 hour of incubation of the catalase with 150 μM NO₂^– at 37°C. Data points were expressed as % of control and represent the mean of three replicates. (C, D) To exclude that the downregulation of NO production is caused by oxidation of nitrite to nitrate, a reduction step of nitrate to nitrite with vanadium chloride was performed. C and D contain the same data expressed as a linear plot depicting original data for nitrite concentration and a logarithmic plot normalized to 100%. Results represent the mean ± SEM of five experiments. Statistical analysis was carried out using unpaired t-test. NO: Nitric oxide.