Cytochromes P450 reductases

The microsomal fraction consists mainly of vesicles (microsomes) derived from the endoplasmic reticulum (smooth and rough). It contains cytochrome P450 and NADPH/cytochrome P450 reductase (collectively the microsomal monooxygenase system), carboxylesterases, A-esterases, epoxide hydrolases, glucuronyl transferases, and other enzymes that metabolize xenobiotics. The 105,000 g supernatant contains soluble enzymes such as glutathione-5-trans-ferases, sulfotransferases, and certain esterases. The 11,000 g supernatant contains all of the types of enzyme listed earlier. 

Superoxide is formed (reaction 1) in the red blood cell by the auto-oxidation of hemoglobin to methemo-globin (approximately 3% of hemoglobin in human red blood cells has been calculated to auto-oxidize per day) in other tissues, it is formed by the action of enzymes such as cytochrome P450 reductase and xanthine oxidase. When stimulated by contact with bacteria, neutrophils exhibit a respiratory burst (see below) and produce superoxide in a reaction catalyzed by NADPH oxidase (reaction 2). Superoxide spontaneously dismu-tates to form H2O2 and O2 however, the rate of this same reaction is speeded up tremendously by the action of the enzyme superoxide dismutase (reaction 3). Hydrogen peroxide is subject to a number of fates. The enzyme catalase, present in many types of cells, converts... 

Cytochrome P450s catalyze reactions that introduce one atom of oxygen derived from molecular oxygen into the substrate, yielding a hydroxylated product. NADPH and NADPH-cytochrome P450 reductase are involved in the complex reaction mechanism. 

Yamazaki, H., Ueng, Y.F., Shimada, T. and Guengerich, F.P. (1995) Roles of divalent metal ions in oxidations catalyzed by recombinant cytochrome P450 3A4 and replacement of NADPH-cytochrome P450 reductase with other flavoproteins, ferredoxin, and oxygen surrogates. Biochemistry, 34, 8380—8389. 

Voznesensky, A.I. and Schenkman, J.B. (1992) Inhibition of cytochrome P450 reductase by polyols has an electrostatic nature. European Journal of Biochemistry, 210, 741—746. 

E. G., Creation of polarized cells coexpressing CYP3A4, NADPH cytochrome P450 reductase and MDRl/P-glycoprotein, Pharm. Res. 2000, 37, 803-810. 

The answers are 34-g, 35-a, 36-d. (Katzung, pp 53—56J There are four major components to the mixed-function oxidase system (1) cytochrome P450, (2) NAD PH, or reduced nicotinamide adenine dinucleotide phosphate, (3) NAD PH—cytochrome P450 reductase, and (4) molecular oxygen. The figure that follows shows the catalytic cycle for the reactions dependent upon cytochrome P450. 

NAD PI I gives up hydrogen atoms to the flavo protein NADPH— cytochrome P450 reductase and becomes NADP+. The reduced flavo protein transfers these reducing equivalents to cytochrome P450. The reducing... 

URBAN, P., MIGNOTTE, C., KAZMAIER, M., DELORME, F., POMPON, D., Cloning, yeast expression, and characterization of the coupling of two distantly related Arabidopsis thaliana NADPH-cytochrome P450 reductases with P450 CYP73A5, Bio. Chem., 1997,272, 19176-86. 

ROSCO, A., PAULI, H.H., PRIESNER, W., KUTCHAN, T.M., Cloning and heterologous expression of cytochrome P450 reductases from the Papaveraceae, Arch. Biochem. Biophys., 1997, 348, 369-377. 

McGuire, J., Anderson, D. J., MacDonald, B. J., Narayanasami, R., Bennett, B. M., Inhibition of NADPH-cytochrome P450 reductase and glyceryl trinitrate biotransformation by diphenyleneiodonium sulfate. 

If cyclohexanecarboxaldehyde is incubated with CYP2B4, NADPH, and cytochrome P450 reductase, the aldehyde-cyclohexyl ring carbon-carbon bond is cleaved generating cyclohexene and formic acid (150) (Fig. 4.81). The reaction is supported if hydrogen peroxide replaces NADPH and cytochrome P450 reductase but is not supported if other oxidants at the same oxidation equivalent as peroxide but bypass the peroxy form of P450 such as iodosobenzene, m-chloroperbenzoic acid, or cumyl hydroperoxide are used. These... 

NADPH controls the protein interaction properties of human cytochrome P450 reductase. Biochemistry, 45 (5), 1421-1434. 

Guengerich, F.P. (2005) Reduction of cytochrome b5 by NADPH-cytochrome P450 reductase. Archives of Biochemistry and Biophysics, 440 (2), 204-211. 

Although mammalian CYPs are attractive candidates for use as commercial biocatalysts, many functional characteristics limit the opportunities to exploit such a system. Association of the enzymes with membranes prevents easy extraction and purification and limits the opportunities to produce useful recombinant enzymes by cloning the relevant genes for expression in microbial systems. All P450s have a porphyrin-haem active site that requires a second protein to reduce the iron component, often cytochrome P450 reductase or... 

Rat brain DT-diaphorase enzyme hypothesized to be cytochrome P450 reductase (Kemp... 

NADPH-cytochrome P450 reductase was purified from rat brain microsomes. 

High NADPH cytochrome P450 reductase activity is found in immature rat brain and neuronal cultures, but very little cytochrome P450, thus NADPH cytochrome P450 reductase may be involved in cytochrome P450 independent pathways (Ghersi-Egea et al., 1993). 

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