Nitric oxide synthase (NOS) shows similarities to cytochrome P-450 reductase. The two enzymes catalyze the oxidation of N-omega-hydroxy-L-arginine by NADPH and oxygen to nitric oxide (NO) and citrulline. Nitric oxide synthase activity is inhibited by L-arginine analogs like N-omega-nitro-L-arginine, which does not affect cytochrome P-450 reductase. Dihydroergotamine, miconazole, and troleandomycin are classical inhibitors of cytochrome. The present study shows the concentration-dependent inhibitory effect of these compounds and of L- but not D-N-omega-nitro-arginine on the activity of constitutive nitric oxide synthase from bovine aortic endothelial cells. Activity of nitric oxide synthase was estimated by measurement of conversion of [3H]arginine to [3H]citrulline. The tested cytochrome P-450 inhibitors are likely to interfere with heme of nitric oxide synthase. The data confirms a similarity as well as functional differences between the enzymes.
This communication examines the possibility that nitric oxide (NO) production by endothelial cells results from changes in cell membrane fluidity. Lysophosphatidylcholine (LPC) alters fluidity of the endothelial cell membranes causing vascular relaxation. Through membrane alterations LPC influences function of a number of membrane receptors and modulates enzyme activity. As a result of detergent action, lysophosphatidylcholine (LPC) causes activation of guanylate cyclase, stimulates sialyltransferase and regulates protein kinase C activity. It has already been demonstrated that ionic detergents, such as Triton X-100 also cause vascular relaxation, possibly induced by NO production from endothelial cells. It is postulated that production of nitric oxide results from changes in membrane viscosity; this may represent a mechanism for its regulation in biological systems.
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