Hydroxylation of fatty acids

A high content of dicarboxylic acid is the most characteristic feature of the composition of aliphatic components of suberin (231). The generation of dicarboxylic acids by oxidation of endogenous cu-hydroxy fatty acids has been demonstrated in cell-free preparations from the excised epidermis of Vida faba leaves (242). This dehydrogenase activity, which showed a strong preference for NADP, was located in the 100000-g supernatant. Modification of the substrate, o -hydroxyhex-adecanoic acid, by removal or esterification of the carboxyl or incorporation of a hydroxyl moiety at C-10, rendered it a poor substrate. cu-Oxohexadecanoic acid could be trapped by dinitrophenylhydrazine, indicating that the oj-oxo acid was probably an intermediate in the reaction. Additionally, synthetic co-oxohex-adecanoic acid was converted to Cjg dicarboxylic acid by the enzyme preparation. 

Wound-healing slices of Solanum tuberosum were utilized to isolate the enzymes involved in dicarboxylic acid generation since they were known to develop a suberin polymer under controlled conditions (243). Extracts of wound-healing slices of S. tuberosum catalyzed a two-step oxidation of cu-hydroxy acid to the dicarboxylic acid with the cu-oxo acid as an intermediate (3). Both steps were cata- 

It was found to be a dimer composed of two 30000 MW monomers. The apparent Kjn values for NADP, cohydroxyhexadecanoic acid, NADPH, and cu-oxohex-adecanoic acid were 100, 20, 5, and 7 pM, respectively. Surprisingly, hydride from the A side of NADPH was added to cu-oxohexadecanoic acid by the purified enzyme at almost the same rate as that from the B side. 

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Chuang SS, Helvig C, Taimi M, Ramshaw HA, Collop AH, et al. 2004. CYP2U1, a novel human thymus- and brain-specific cytochrome P450, catalyzes omega- and (omega-1)-hydroxylation of fatty acids. J Biol Chem 279 6305-6314. 

Another source of rubredoxins was found in an aerobic bacterium, Pseudomonas oleovorans, utilizing n-hexane as a carbon source (10). This particular rubredoxin differs from those commonly found in anaerobic bacteria in some of its properties it has a molecular weight of 19,000, and one iron form of the protein is readily converted to a two-iron form (11). The rubredoxin of P. oleovorans functions as a terminal electron transfer component in an enzyme system which participates in the ( -hydroxylation of fatty acids and hydrocarbons. The hydrocarbon-oxidizing... 

Leal W. S., Zarbin P. H. G., Wojtasek H. and Ferreira J. T. (1999) Biosynthesis of scarab beetle pheromones enantioselective 8-hydroxylation of fatty acids. Eur. J. Biochem. 259, 175-180. 

Cabello-Hurtado, F., Batard, Y., Salaun, J.P., Durst, F., Pinot, F., and Werch-Reichhart, D., Cloning, expression in yeast, and functional characterization of CYP81B1, a plant cytochrome P450 that catalyzes inchain hydroxylation of fatty acids, J. Biol. Chem., 273, 7260-7267, 1998. 

Miura, Y., and Fulco, A. J. 1974. (Omega-2) Hydroxylation of Fatty-Acids by a Soluble System from Bacillus megaterium. J. Biol. Chem., 249,1880-1888. 

These screens have been used to direct the evolution of cytochrome P450 BM-3, a soluble enzyme from Bacillus megaterium that contains its reductase and hydroxylase domains on a single polypeptide chain. P450 BM-3 primarily catalyzes the hydroxylation of fatty acids ( 12 to 18 carbons long) at the a>-1, a>-2, and m-3 positions, but also... 

They convert cholesterol to bile acids and convert vitamin prostaglandins, and many other metabolites to more soluble and often biologically more active forms. In plants cytochromes P450 participate in hydroxylation of fatty acids at many positions. ... 

Matsunaga, I., M. Yamada, E. Kusunose, Y. Nishiuchi, 1. Yano, and K. Ichihara (1996). Direct involvement of hydrogen peroxide in bacterial a-hydroxylation of fatty acid. FEBS Lett. 386, 252-254. 

Expression of rabbit cytochrome P4504A which catalyzes the oo-hydroxylation of fatty acids, and prostaglandins. Arch. Biochem. Biophys. 307, 57-67. 

In contrast to the large amount of the three-dimensional structural data available in the literature, little is known about the physiological fimction of Rd. Typically, Rds exhibit redox potentials in the range of —60 to OmV [24], and are commonly assmned to be involved in electron transfer processes. It has bear demonstrated that Rd can replace ferredoxin as an electron carrier in certain electron transfer reactions [3]. Furthermore, Rd from the aerobe P. oleovorans was proposed to participate in the ctj-hydroxylation of fatty acids and hydrocarbons by transferring electrons to an alkane hydroxylase [7, 25]. Rd isolated from D. gigas was also shown to be involved in the formation of ATP from the degradation of polyglucose in the presence of... 

A distorted tetrahedral environment of sulfur ligands was found for rubredoxin, which contains [IFe-OS] and is an intermediate electron carrier in the co-hydroxylation of fatty acids in Pseudomonas oleovorans. Fe cycles between the Fe(II) and Fe(Ill) states with E°= + 20 mV vs. NHE in the protein... 

Quantitative studies show that only a small fraction of the fatty acids are subject to co-oxidation in the liver under normal conditions [387]. Starvation, diabetes mellitus and ketosis apparently augment co-oxidation of fatty acids in experimental animals and man [388-390]. In these situations, several investigators estimated that 10-40% of the fatty acids may be initially co-oxidised [388,389,392]. The increase was probably not due to induction of the monooxygenase enzymes but could reflect a decreased rate of formation of fatty acid esters for reacylation [390]. However, monooxygenase metabolism of fatty acids is inducible. Treatment with pheno-barbital increased the hepatic co2-hydroxylation, while the col-hydroxylation of fatty acids was little affected [374]. Renal cortical hydroxylation of fatty acids could be induced by a high intake of fat in the diet [393]. 

Unlike 1- and fatty acids, it is not known whether epoxides of essential fatty acids are formed by monooxygenases in vivo. However, isolated renal cells and hepatocytes of the rat metabolise exogenous arachidonic acid to 11,12-dihydroxy- and 14,15-dihydroxy-eiCosatrienoic acids [402], Surprisingly, the capacity of renal cells to form these 1,2-diols was several times higher than that of the isolated hepatocytes. 

M. K. Moe, T. Anderssen, M. B. Str0m, and E. Jensen, Total structure characterization of unsaturated acidic phospholipids provided by di-hydroxylation of fatty acid double bonds and negative electrospray ionization mass spectrometry, J. Am. Soc. Mass Spectrom. 16, 46-59 (2005). 

Eujishiro T, Shoji O, Nagano S, Sugimoto H, Shiro Y, Watanabe Y (2011) Crystal structure of H202-dependent cytochrome P450SPalpha with its bound fatty acid substrate insight into the regioselective hydroxylation of fatty acids at the alpha position. J Biol Chem 286 29941-29950... 

Li H, Pinot F, Sauveplane V, Werck-Reichhart D, Diehl P, Schreiber L, Franke R, Zhang P, Chen L, Gao Y Liang W, Zhang D (2010) Cytochrome P450 family member CYP704B2 catalyzes the co-hydroxylation of fatty acids and is required for anther cutin biosynthesis and pollen exine formation in rice. Plant Cell 22 173-190... 

The co-hydroxylation of fatty acids, which involves the addition of a hydroxyl group at or near the co-terminal carbon, was first shown to be catalyzed by the liver microsomal enzyme system in the 1960s [38], In particular, the CO pigment of CYP was recognized as a constituent of the microsomal mixed function oxidase system that contributes to the co-hydroxylation of steroids [39], Substrates that are susceptible to co-hydroxylation include laurate and AA [38], Early reports showed that CYP enzymes catalyze the CO (C-20) and co-1 (C-19) hydroxy lation of AA [40], In 1990, Faick et al. demonstrated that CYP enzymes also hydroxy late the C-16 (co-4), C-17 (co-3), and C-18 (co-2) carbons of A A [41], Thus, in the presence of nicotinamide adenine dinucleotide phosphate (NADPH) and molecular oxygen, CYPs mediate the hydroxylation of AA to generate a variety of co-terminal HETEs including 16-, 17-, 18-, 19-, and 20-HETR (Fig. 13.2). 

A specific hepatic microsomal isoenzyme of cytochrome P450 (termed CYP4A1 or P452) with a narrow substrate specificity for oi-hydroxylation of fatty acids was induced by peroxisome proliferators clofibrate (Gibson et al. 1982, 1990, Tamburini et al. 1984, Gibson 1992) and phthalates. 

The liver mixed-function oxidase system catalyzes the hydroxylation of fatty acids, hydrocarbons (see section on carcinogenesis in Chapter 16), and many drugs. Because of their broad involvement in metabolism, mixed-function oxidases have been researched so extensively that even a superficial review of the published work is impossible. For further information, the reader is referred to specialized texts [193]. 

Soliday C L, Kolattukudy P E 1977 Biosynthesis of cutin. cu-Hydroxylation of fatty acids by a microsomal preparation from germinating Vida faba. Plant Physiol 59 1116-1121... 

Another alternative method to hydroxylation of fatty acids is the hydroformylation, which allows the introduction... 

Faulkner KM, Shet MS, Fisher CW, Estabrook RW (1995) Electrocatalytically driven omega-hydroxylation of fatty acids using cytochrome P450 4A1. Proc Nat Acad Sci USA... 

Efforts to solubilize and isolate the P-450 monoxygenases from the microsomal membranes have been hampered by the facile conversion to a catalytically inactive form, cytochrome P-420. In 1968, however, a successful solubilization of catalytically active P-450 from hepatic microsomes was reported.30, 31 he solubilized system, which effected w-hydroxylation of fatty acids, required three coiq>onents for catalytic activity cytochrome P-450, NADPH-cytochrome c reductase, and a heat-stable, chloroform-soluble factor, the active component of which was identified as the microsomal lipid phosphatidylcholine.32 Further studies with this solubilized and reconstituted system have Indicated that the cytochrome P-450 and P-448 fractions have different catalytic activities 33-35 and that the terminal oxidase activity resides in the b-type cytochrome (P-450 or P-448) fraction rather than the cytochrome c reductase or lipid fractions.33, 36, 37 xhe cytochrome P-450 and P-448 were found to coiq>ete for reductase when present together.38 Cytochrome bs did not appear to be an obligatory component of the reconstituted systera.39 Cytochrome P-450 and P-448 fractions from rat liver were found to contain high levels of an epoxide hydrase, which can convert intermediate oxides to vicinal diols. Further purification has afforded fractions relatively free of cross-contamination of monoxygenase and hydrase enzymes. Recently, differential solubilization of monoxygenase activity towards a Type I substrate (naphthalene) and a Type II substrate (aniline) was... 

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