Purity >99%. L-NNA is a competitive inhibitor of nitric oxide synthase (NOS) with selectivity for the neuronal and endothelial isoforms of the enzyme. Although L-NAME is much more soluble than L-NNA in aqueous systems, a hydrolysis step is required to activate L-NAME, thus adding complexity to an in vivo experiment. L-NNA inhibits nNOS, eNOS, and iNOS with Ki values of 15 nM (bovine), 39 nM (human), and 4.4 μM (mouse), respectively.