Molecular cloning and functional expression of an inducible nitric oxide synthase from a murine macrophage cell line

Macrophages activated by exposure to cytokines and/ or to endotoxin produce nitric oxide (NO^•), a free radical that is a mediator of the host response to infection. Activation induces the expression of nitric oxide synthase, the enzyme that catalyzes formation of NO^• from L-arginine and molecular oxygen. We report the cloning of a cDNA encoding the inducible nitric oxide synthase from a murine macrophage cell line, RAW264.7, exposed to interferon-γ and lipopolysaccharide. Oocytes injected with mRNA transcribed from this cDNA demonstrate arginine-dependent production of nitrite, a stable metabolite of NO^•. Nitrite production is blocked by the enzyme inhibitor, N^G-monomethylarginine, and is independent of calcium/calmodulin. RAW264.7 cells demonstrate rapid accumulation of the nitric oxide synthase-encoding mRNAs upon activation. Comparison of the deduced amino acid sequence to the calcium/calmodulin-dependent nitric oxide synthase previously purified (Bredt, D. S., and Snyder, S. H. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 682-685) and cloned (Bredt, D. S., Hwang, P. M., Glatt, C. E., Lowenstein, C., Reed, R. R., and Synder, S. H. (1991) Nature 351, 714-718) from rat brain identifies shared binding sites for the cofactors NADPH and flavins in the C-terminal half of both proteins and an additional conserved region near the N terminus that may recognize L-arginine and/or contribute to the active site.