26- Hydroxylation cytochrome

Fasan, R., Chen, M.M., Crook, N.C. et al. (2007) Engineered alkane-hydroxylating cytochrome P450 (BM3) exhibiting nativelike catalytic properties. Angewandte Chemie (International Edition in English), 46 (44), 8414-8418. 

Dayer P, Desmeules J, Leemann T, Stribemi R. 1988. Bioactivation of the narcotic drug codeine in human liver is mediated by the polymorphic monooxygenase catalyzing debrisoquine 4-hydroxylation (cytochrome P-450 dbl/ bufl). Biochem Biophys Res Commun 152 411-416. 

Matsunaga I, Ueda A, Fujiwara N, Sumimoto T, Ichihara K (1999) Characterization of the ybdT gene product of Bacillus subtilis novel fatty acid (3-hydroxylating cytochrome P450. Lipids 34 841-846... 

The studies referred to were performed with crude preparations of cytochrome P-450. In a series of papers Wikvall, Hansson and collaborators have reported studies on 7a-hydroxylation of cholesterol in highly purified preparations of cytochrome P-450 from rats and rabbits [82,84,85], They showed that electrophoretically homogenous cytochrome P-450 LM4 isolated from cholestyramine-treated rabbits catalyses 7 -hydroxylation of cholesterol as well as some other hydroxylations. Chromatography of a cytochrome P-450 LM4 fraction on octylamine-Sepharose resulted in 2 subfractions, cytochrome P-450 LM4 I and cytochrome P-450 LM4 II, with different catalytic properties. Cytochrome P-450 LM4 I was unable to catalyse 7a-hydroxylation of cholesterol, but catalysed 12a- and 25-hydroxylations. Cytochrome P-450 LM4 II efficiently catalysed cholesterol 7a-hydroxylation. It also catalysed the other hydroxylations, although at lower rates than the original cytochrome P-450 LM4. 

Birgersson, C., E.T. Morgan, H. Jornvall, and C. von Bahr (1986). Purification of a desmethylimipramine and debrisoquine hydroxylating cytochrome P-450 from human liver. Biochem. Pharmacol. 35, 3165-3166. 

Many of the enzyme systems of the biosynthetic process have now been studied. A microsomal fraction from etiolated sorghum seedlings converted L-tyrosine (2) into p-hy-droxymandelonitrile (3) (Halkier and Mpller, 1991 Mpller and Poulton, 1993). The particles required only NADPH in addition to the substrate.. /V-Hydroxytyrosine (4) was shown to be an intermediate in the synthesis of the aldoxime, and an N-hydroxylating cytochrome P-450 was identified (Dewick, 1984 Halkier and M0ller, 1989,1991 Halkier et al, 1991). The A -hydroxytyrosine (4) is converted to 2-nitro-3-(p-hy-droxyphenyl)propionic acid (5), which is, in turn, converted to l-ad-nitro-2-(p-hydroxyphenyl)ethane (6). The last compound appears to be the immediate precursor to ( )-p-hy-... 

Yasutake Y, Kitagawa W, Hata M, Nishioka T, Oza-ki T, Nishiyama M, Kuzuyama T, Tamura T (2014) Structure of the quinoline N-hydroxylating cytochrome P450 RauA, an essential enzyme that confers antibiotic activity on aurachin alkaloids. FEBS Lett 588 105-110... 

Vims, C. and Bernhardt, R. (2008) Molecular evolution of a steroid hydroxylating cytochrome P450 using a versatile steroid detection system for screening. Lipids, 43 (12), 1133-1141. 

Fasan R, Chen MM, Crook NC, Arnold FH. Engineered alkane-hydroxylating cytochrome P450BM3 exhibiting... 

As a class of compounds, the two main toxicity concerns for nitriles are acute lethality and osteolathyrsm. A comprehensive review of the toxicity of nitriles, including detailed discussion of biochemical mechanisms of toxicity and stmcture-activity relationships, is available (12). Nitriles vary broadly in their abiUty to cause acute lethaUty and subde differences in stmcture can greatly affect toxic potency. The biochemical basis of their acute toxicity is related to their metaboHsm in the body. Following exposure and absorption, nitriles are metabolized by cytochrome p450 enzymes in the Hver. The metaboHsm involves initial hydrogen abstraction resulting in the formation of a carbon radical, followed by hydroxylation of the carbon radical. MetaboHsm at the carbon atom adjacent (alpha) to the cyano group would yield a cyanohydrin metaboHte, which decomposes readily in the body to produce cyanide. Hydroxylation at other carbon positions in the nitrile does not result in cyanide release. 

N—Fe(IV)Por complexes. Oxo iron(IV) porphyrin cation radical complexes, [O—Fe(IV)Por ], are important intermediates in oxygen atom transfer reactions. Compound I of the enzymes catalase and peroxidase have this formulation, as does the active intermediate in the catalytic cycle of cytochrome P Q. Similar intermediates are invoked in the extensively investigated hydroxylations and epoxidations of hydrocarbon substrates cataly2ed by iron porphyrins in the presence of such oxidizing agents as iodosylbenzene, NaOCl, peroxides, and air. 

Hydroxy vitamin D pools ia the blood and is transported on DBF to the kidney, where further hydroxylation takes place at C-1 or C-24 ia response to calcium levels. l-Hydroxylation occurs primarily ia the kidney mitochondria and is cataly2ed by a mixed-function monooxygenase with a specific cytochrome P-450 (52,179,180). 1 a- and 24-Hydroxylation of 25-hydroxycholecalciferol has also been shown to take place ia the placenta of pregnant mammals and ia bone cells, as well as ia the epidermis. Low phosphate levels also stimulate 1,25-dihydtoxycholecalciferol production, which ia turn stimulates intestinal calcium as well as phosphoms absorption. It also mobilizes these minerals from bone and decreases their kidney excretion. Together with PTH, calcitriol also stimulates renal reabsorption of the calcium and phosphoms by the proximal tubules (51,141,181—183). 

In the endoplasmic reticulum of eukaryotic cells, the oxidation of the terminal carbon of a normal fatty acid—a process termed ch-oxidation—can lead to the synthesis of small amounts of dicarboxylic acids (Figure 24.27). Cytochrome P-450, a monooxygenase enzyme that requires NADPH as a coenzyme and uses O, as a substrate, places a hydroxyl group at the terminal carbon. Subsequent oxidation to a carboxyl group produces a dicarboxylic acid. Either end can form an ester linkage to CoA and be subjected to /3-oxidation, producing a... 

The overall hydroxylation or epoxidation reaction catalyzed by cytochrome P450s involves the insertion of one oxygen atom, derived from molecular oxygen, into a C-H bond or into the Jt-system of an olefin, with the concomitant reduction of the... 

Scheme 10.2 Cytochrome P450cam-catalyzed hydroxylation of camphor.

Many examples of microbial hydroxylation of sterols/steroids have been reported. These hydroxylations usually involve mixed function oxidases which utilise molecular oxygen and cytochrome P-450. The reaction can be represented by ... 

The metabolism of foreign compounds (xenobiotics) often takes place in two consecutive reactions, classically referred to as phases one and two. Phase I is a functionalization of the lipophilic compound that can be used to attach a conjugate in Phase II. The conjugated product is usually sufficiently water-soluble to be excretable into the urine. The most important biotransformations of Phase I are aromatic and aliphatic hydroxylations catalyzed by cytochromes P450. Other Phase I enzymes are for example epoxide hydrolases or carboxylesterases. Typical Phase II enzymes are UDP-glucuronosyltrans-ferases, sulfotransferases, N-acetyltransferases and methyltransferases e.g. thiopurin S-methyltransferase. 

The numerous biotransformations catalyzed by cytochrome P450 enzymes include aromatic and aliphatic hydroxylations, epoxidations of olefinic and aromatic structures, oxidations and oxidative dealkylations of heteroatoms and as well as some reductive reactions. Cytochromes P450 of higher animals may be classified into two broad categories depending on whether their substrates are primarily endogenous or xenobiotic substances. Thus, CYP enzymes of families 1-3 catalyze... 

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