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PubMed · 1380405

Ca2+/calmodulin-regulated nitric oxide synthases.

H H Schmidt·J S Pollock·M Nakane·U Förstermann·F Murad
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Abstract

NO synthase (NOS) catalyzes the oxidation of L-arginine to L-citrulline and nitric oxide (NO) or a NO-releasing compound. At least three isoforms of NOS exist (types I-III). The activities of the type I isoform purified from brain and the type III isoform purified from endothelial cells are regulated by the intracellular free calcium concentration ([Ca2+]i) and the Ca(2+)-binding protein calmodulin. At resting [Ca2+]i, both isozymes are inactive; they become fully active at [Ca2+]i greater than or equal to 500 nM Ca2+. Longer lasting increases in [Ca2+]i may downregulate NO formation, for in vitro phosphorylation by Ca2+/calmodulin protein kinase II decreases the Vmax of NOS. Besides the conversion of L-arginine, type I NOS, Ca2+/calmodulin dependently, generates H2O2 and reduces cytochrome c/P450. Other redox activities, i.e. the reduction of nitroblue tetrazolium to diformazan (NADPH-diaphorase) or of quinoid-dihydrobiopterin to tetrahydrobiopterin, by NOS appear to be Ca2+/calmodulin-independent.

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Amino Acid OxidoreductasesCalciumCalmodulinNitric Oxide SynthaseJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.Review

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H H Schmidt, J S Pollock, M Nakane, U Förstermann, F Murad. Ca2+/calmodulin-regulated nitric oxide synthases.. https://doi.org/10.1016/0143-4160(92)90055-w

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