Cytochrome interaction with P450 reductase

As discussed in Sect. 7.44.4 (vide supra), one of the mechanistic curiosities is the interaction of cytochrome b with P450 17A1, which (in part) regulates the balance between the 17a-hydroxy and 17,20-lyase products. An NMR study with cytochrome b led to the conclusion that the protein occupies a position at a site on P450 17A1, including Arg-347, Arg-358, and Arg-449 [2178]. The same site is believed to be occupied by NADPH-P450 reductase. 

Davydov, D.R., Kariakin, A.A., Petushkova, N.A. and Peterson, J.A. (2000) Association of cytochromes P450 with their reductases opposite sign of the electrostatic interactions in P450BM-3 as compared with the microsomal 2B4 system. Biochemistry, 39 (21), 6489-6497. 

D. Active Site Environment Human HO-1 Crystal Structure Interaction with Cytochrome P450 Reductase Gaseous Ligands... 

Brimfield, A.A., Novak, M.J., Mancebo, A.M., Gallagher, B.S., Arroyo, M. (2006). The detection of free radical formation from the interaction of sulfur mustard with NADPH-cytochrome P450 reductase. Toxicologist 90 391. 

Mao, W., Rupasinghe, S.G., Zangerl, A.R., Berenbaum, M.R. and Schuler, M.A. (2007) Allelic variation in the Depressaria pastinacella CYP6AB3 protein enhances metabolism of plant allelochemicals by altering a proximal surface residue and potential interactions with cytochrome P450 reductase. /. Biol. Chem., 282,10544—52. 

NADPH cytochrome P450 reductase, an enzyme containing which a complex flavoenzyme that contains two flavins, one electron is first intramolecularly transferred from FAD to FMN, before the reaction with cytochrome P450 takes place. With FNR, NADP+ first has to bind to the oxidized form, before the very fast one-electron transfer from the specifically interacting reduced ferredoxin (Fdred) occurs (8). Subsequent dissociation of the oxidized ferredoxin (Fdox) is rate-limiting in catalysis. The enzyme semiquinone-NADP" complex then reacts with another reduced ferredoxin molecule to yield the flavin hydroquinone state. In the final steps of the catalytic cycle, the NADP+ is reduced and the NADPH dissociates ... 

Shimizu, T., T. Tateishi, M. Hatano, and Y. Fujiikuriyama (1991). Probing the role of lysines and arginines in the catalytic function of cytochrome-P450d by site-directed mutagenesis— interaction with NADPH-cytochrome-P450 reductase.,/ Sto/. Chem. 266, 3372-3375. 

Backes, W.L., C.J Batie, and G.F. Cawley (1998). Interactions among P450 enzymes when combined in reconstituted systems Formation of a 2B4-1A2 complex with a high affinity for NADPH cytochrome P450 reductase. Biochemistry 37, 12852-12859. 

CYP oxidation reactions involve a complex series of steps that have been well defined Rose and Hodgson, 2004). The initial step involves the binding of substrate to oxidized CYP, followed by a one-electron reduction catalyzed hy NADPH cytochrome P450 reductase to form a reduced cytochrome-substrate complex. The next several steps involve interaction with molecular oxygen, the acceptance of a second electron from NADPH cytochrome P450 reductase or NADH cytochrome b reductase, followed by the subsequent release of water and the oxygenated product of the reaction. This complicated reaction sequence results in the transfer of one atom of molecular oxygen to the substrate while the other atom is reduced to water. 

---