Nitric oxide arginine, binding site

In 1989, BH4 was found to be a cofactor for nitric oxide synthase (NOS) [ 126, 127]. BH4 is also involved in dimerization of NOS, as NOS is catalytically active in a homodimer structure. Three isoforms of NOS exist neuronal NOS (NOS 1), inducible NOS (NOS 2) and endothelial NOS (NOS 3). BH4 is essential for all NOS isoforms. The NOS isoforms share approximately 50-60% sequence homology. Each NOS polypeptide is comprised of oxygenase and reductase domains. An N-terminal oxygenase domain contains iron protoporphyrin IX (heme), BH4 and an arginine binding site, and a C-terminal reductase domain contains flavin mononucleotide (FMN), and a reduced nicotin-amide adenine dinucleotide phosphate (NADPH) binding site. 

Berka V, Tsai AL (2000) Characterization of interactions among the heme center, tetrahydrobiopterin, and /.-arginine binding sites of ferric eNOS using imidazole, cyanide, and nitric oxide as probes. Biochemistry 39 9373-9383... 

FIGURE I Schematic alignment of the deduced amino acid sequences of nitric oxide synthases (NOSs) and the cytochrome P-450 reductase. Depicted are consensus binding sites for heme, L-arginine, calmodulin (CaM), flavin mononucleotide (FMN), flavin-adenine dinucleotide (FAD), and NADPH. An NH2-terminal myristoylation site (myr) is present only in the endothelial constitutive NOS (ecNOS). n. Neuronal i, inducible. 

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