NADPH consumption by eNOS can be blocked by BH4 in absence of L-arginine.

3μg WT eNOS or S1179D eNOS mixed with 600μL reaction system containing 50 mM Tris-HCl, pH 7.4, 0.5 mM NADPH, 0.5mM Ca²⁺, 10μg/ml calmodulin, and BH4 at the indicated concentrations. NADPH consumption was monitored spectrophotometrically at 340nm. (A and B) BH4 showed a dose-dependent inhibitory effect on both WT eNOS and S1179D eNOS, although they had different NADPH consumption rates. (C) S1179D eNOS had a significantly higher NADPH consumption rate than WT eNOS, and was less sensitive to BH4 than WT eNOS. Data shown are the mean ± S.E. from five independent experiments.