Cloned and expressed macrophage nitric oxide synthase contrasts with the brain enzyme.

Nitric oxide (NO) is a messenger molecule of macrophages, endothelial cells in blood vessels, and neurons. A neuronal form of NO synthase (NOS) has been previously cloned. We now report the molecular cloning of macrophage NOS. The macrophage enzyme displays 50% sequence identity to the neuronal enzyme. Like neuronal NOS, macrophage NOS has recognition sites for FAD, FMN, and NADPH and also has a consensus calmodulin binding site. Macrophage NOS mRNA is strikingly inducible; it is absent in quiescent macrophages or spleen but is prominent 2-6 hr after endotoxin treatment.