Autoinhibition of neuronal nitric oxide synthase: distinct effects of reactive nitrogen and oxygen species on enzyme activity

Abstract

Nitric oxide (NO) synthases (NOSs), which catalyse the oxidation of -arginine to -citrulline and an oxide of nitrogen, possibly NO or nitroxyl (NO − ), are subject to autoinhibition by a mechanism that has yet to be fully elucidated. In the present study we investigated the actions of NO and other NOS-derived products as possible autoregulators of enzyme activity. With the use of purified NOS-I, -arginine turnover was found to operate initially at V max (0-15 min, phase I) although, despite the presence of excess substrate and cofactors, prolonged catalysis (15-90 min, phase II) was associated with a rapid decline in -arginine turnover. Taken together, these observations suggested that one or more NOS products inactivate NOS. Indeed, exogenously applied reactive nitrogen oxide species (RNSs) decreased V max during phase I, although with different potencies (NO − NO ONOO − ) and efficacies (NO NO − l ONOO − ). The NO scavengers oxyhaemoglobin (HbO # ; 100 µM) and 1H-imidazol-1-yloxy-2-(4-carboxyphenyl)-4,5-dihydro-4,4,5,5-tetramethyl-3-

Tianma Gouteng Decoction Exerts Pregnancy-Protective Effects Against Preeclampsia via Regulation of Oxidative Stress and NO Signaling

“…To explore the mechanisms underlying TGD in regulation of NO production, we examined the effect of TGD on TNOS enzymatic activity using a commercial kit. Our results exhibited that H 2 O 2 treatment (500 μM, 3 h) significantly suppressed TNOS activity, which was consistent with a previous report ( Kotsonis et al, 1999 ), while TGD treatment not only significantly up-regulated TNOS activity but also effectively restored the H 2 O 2 -suppressed TNOS activity ( Figure 3A ), indicating TGD regulates TNOS activity. Consistently, treatment with L-NAME, an inhibitor of TNOS activity ( Pfeiffer et al, 1996 ), significantly lowered the TGD-induced NO levels, compared with the TGD-treatment group ( Figure 3B ).…”

Effect of nitroxyl on the hamster retinal nitridergic pathway

“…Since HNO may be synthesized during the NOScatalyzed oxidation of L-arginine under certain cofactor conditions (Adak et al, 2000), the inhibition of NOS by HNO may be another pathway of NOS auto inhibition. Kotsonis et al showed that low concentrations of HNO and NO decrease the activity of neuronal NOS (nNOS or NOS-1) purified from pig cerebellum (Kotsonis et al, 1999). We extend this conclusion by showing that both compounds were effective even in retinal homogenates.…”

The vulnerability of nitrergic neurons to transient spinal cord ischemia: a quantitative immunohistochemical and histochemical study

“…-independent NOS (iNOS) in the tissue exists (Lukácová et al 2006). The main mechanism, which could contribute to a decrease of nNOS expression, are (1) autoinhibition of the nNOS activity caused by an excessive formation of NO resulting from iNOS expression, and/or (2) a biological feedback control mechanism by which excessively generated NO can regulate the amount of subsequent NO synthesis (Kotsonis et al 1999). Many other factors, such as the absence of L-arginine, NADPH, FAD and oxygen, and/or the cofactor tetrahydrobiopterin (Marletta 1993;Xia et al 1996) can also contribute to the loss of enzyme expression during ischemia and longer time of reperfusion.…”