Figure 1.

NOS homodimer subdomain structure and electron transfer sequence. Hydride transfer from NADPH to FAD is followed by electron transfer to the FMN subdomain and then to the heme in the oxygenase domain of the partner NOS monomer. Electron transfer from FAD to FMN and from FMN to heme is activated by binding of calmodulin. NOS conformational changes based on electron microscopy structures showing the Input, Calmodulin-Docked, and Output conformations. (Figure adapted with permission from ref. (9))