Nitric oxide synthase (NOS) prokaryotic oxygenase domain. NOS produces nitric oxide (NO) by catalyzing a five-electron heme-based oxidation of a guanidine nitrogen of L-arginine to L-citrulline via two successive monooxygenation reactions producing N(omega)-hydroxy-L-arginine (NHA) as an intermediate. Nitric oxide synthases are homodimers. Most prokaryotes produce NO as a byproduct of denitrification, using a completely different set of enzymes than NOS. However, a few prokaryotes also have a NOS, consisting solely of the NOS oxygenase domain. Prokaryotic NOS binds to the substrate L-Arg, zinc, and to the cofactors heme and tetrahydrofolate.
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