Purity >99%. L-NAME requires hydrolysis of the methyl ester by cellular esterases to become a fully functional inhibitor (L-NNA). L-NNA exhibits some selectivity for inhibition of neuronal and endothelial isoforms. It exhibits Ki values of 15 nM, 39 nM, and 4.4 μM for nNOS (bovine), eNOS (human), and iNOS (mouse), respectively. The reported Ki value for the inhibition of iNOS ranges from 4-65 μM. L-NAME inhibits cGMP formation in endothelial cells with an IC50 of 3.1 μM (in the presence of 30 μM arginine) and reverses the vasodilation effects of acetylcholine in rat aorta rings with an EC50 of 0.54 μM.