Modeling steady-state [NO] as a function of O2 concentration with Cygb-NOD catalysis at a constant NO flux. The steady-state [NO] decreases with a higher Cygb-NOD turnover at higher [O2] (solid line). At low [O2], an elevated steady-state [NO] decreases the O2 : NO ratio (dashed line), and at O2 : NO ratios <500, NO inhibits Cygb-NOD [135]. A higher [Cygb], or lower NO synthesis rate, would be required for Cygb-NOD to maintain an O2 : NO ratio of >500 : 1 at a lower [O2]. Calculations were for 1 M Cygb, s−1 M−1, and a NO synthesis rate of 1.7 µM NO s−1. Calculations were simplified by applying the experimentally measured (O2) = 20 µM to derive a apparent = [O2]/(O2) + [O2] for the various O2 concentrations. The graded NO inhibition of Cygb-NOD is reflected in the apparent (O2), and the effect of O2 on NO synthesis rates are ignored.
