Description_x000D_ Biochem/physiol Actions_x000D_ NOS is responsible for the biosynthesis of nitric oxide from L-arginine and is constituitively expressed in endothelial cells (eNOS) and brain (nNOS)._x000D_ Suitable for measuring NOS activity in the presence of exogenously added co-factors and/or inhibitors._x000D_ Unit Definition_x000D_ One unit of enzyme produces 1 nmole of nitric oxide per minute at 37 °C in 50 mM HEPES, pH 7.4, containing 5 μM oxyhemoglobin, 1 mM CaCl2, 20 μg/ml calmodulin, 0.1 mM NADPH, 50 μM arginine, 12 μM tetrahydrobiopterin, and 170 μM DTT._x000D_ Physical form_x000D_ Solution in 50 mM HEPES, pH 7.4, with 10% glycerol, 5 mM CHAPS, and 100 μM DTT.