Isozymes of Nitric Oxide Synthase (NOS)

Three NOS isozymes are found in animals: neuronal NOS, endothelial NOS, and inducible NOS.

Although they differ  when it comes to amino acid sequence (51-57% homology), they all share similar structures. They are homodimeric with each monomer containing a N-terminal oxygenase domain and a C-terminal reductase domain. The N-terminal oxygenase domain contains binding sites for the catalytic heme, tetrahydrobiopterin (H4B), and the substrates L-arginine and molecular oxygen. The C-terminal domain contains binding sites for cofactors FMN, FAD, and NADPH. A calmodulin binding domain connects the two domains in each monomer.


This view shows the oxygenase domains of the three isozymes superimposed. The monomers are shown in cyan and dark cyan. The heme is colored using cpk coloring, and the pterin is colored pink. Notice the similarity in the structures of the 3 enzymes.  1NOD 2NSE 1OM4

This view shows both monomers of Murine Inducible NOSox.1NOD


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