Domain organization of CYPOR, NOS isoforms, and related enzymes. Dots indicate conserved aromatic amino acid residues and bars above “CD” represent the location of the connecting domains in the primary sequence. H, hinge; C, conseved Cys residue as the thiolate heme ligand; CD, connecting domain. Note that CD consists of two different parts of the linear sequence interspersed with the FNR like domain. (A) Fld, flavodoxin; FNR, ferredoxin-NADP+ oxidoreductase; CYPOR, NADPH-cytochrome P450 oxidoreductase; P450, cytochrome P450; TM, transmembrane domain. (B) CaM, CaM-binding region; H4B, (6R)-5,6,7,8-tetrahydrobiopterin; BF, -finger; AR, autoregulatory region; Myr and Palm, myristoylation and palmitoylation motifs, respectively; Zn, Zinc binding site found at the dimer interface; PDZ, PDZ domain.