Heme oxygenase electronic effects

Three isoforms of NOS are produced in mammalian cells neuronal (nNOS), endothelial (eNOS), and inducible (iNOS) [55]. All NOS isoforms exist as homodimers with a C-terminal FMN-FAD fused reductase domain, an N-terminal oxygenase domain, and a calmodulin binding sequence at the interface of the two domains. The NOS catalytic mechanism is complicated and requires O2, NADPH, FMN, FAD, Ca2+, calmodulin, tetrahydro-biopterin (BH4), and heme to effect the five-electron oxidation of L-arginine to L-citrulline and NO. Consumed in this process are 1.5 equivalents of NADPH and 2 equivalents of O2. 

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