Beta-oxidation pathway

Michael reactions and, 895 Beta-keto ester, 851 alkylation of, 859-860 cyclic, 892-893 decarboxylation of, 857, 860 Michael reactions and. 895 pKd of, 852 synthesis of, 892-893 Beta-lactam antibiotics, 824-825 Beta oxidation pathway, 1133-1137 mechanism of, 1133-1136 Beta-pleated sheet (protein), 1038 molecular model of, 1039 secondary protein structure and, 1038-1039 Betaine, 720 Bextra. structure of, 544 BHA, synthesis of, 629 BHT, synthesis of. 629 Bicycloalkane. 129 Bijvoet. J. M., 299 Bimolecular, 363... 

Figure 17.4 Parallel beta oxidation pathways for a xenobiotic substituted benzene, 5-phenyl pen-tanoic acid, and a naturally occurring fatty acid, stearic acid (Nelson and Cox, 2000).

Dreyer, C., Krey, G., Keller, H., Givel, F., Helftenbein, G., and Wahli, W. (1992). Control of the Peroxisomal Beta-Oxidation pathway by a Novel Family of Nuclear Hormone Receptors. Cell 68, 879-887. 

Beta oxidation proceeds by the sequential removal of two carbon fragments from the functional end of the alkanoic acid. Recent evidence for the existence of an operative oxidative pathway in soils has been reported. The first intermediate of the beta oxidation pathway, 2-4-di-chlorophenoxycrotonic acid, was detected in soils treated with 2,4-dichlor-... 

Bramer CO, Steinbiichel A (2001) The methylcitric acid pathway in Ralstonia eutropha. new genes identified involved in propionate metabolism. Microbiol 147 2203-2214 Brigham CJ, Budde CF, Holder JW, Zeng Q, Mahan AE, Rha C, Sinskey AJ (2010) Elucidation of beta-oxidation pathways in Ralstonia eutropha U16 by examination of global gene expression. J Bacteiiol 192 5454-5464... 

Campbell, J. W., Morgan-Kiss, R. M. Cronan, Jr. J. E. (2003). A new Escherichia coli metabolic competency growth on fatty acids by a novel anaerobic beta-oxidation pathway. Mol Microbiol, 47 793-805. 

Duleimo T, Nicaud JM (2011) Involvement of the G3P shuttle and beta-oxidation pathway in the control of TAG synthesis and lipid accumulation in Yarrowia lipolytica. Metab Eng 13 (5) 482-491. doi 10.1016/j.ymben.2011.05.002... 

Fatty acids obtained by hydrolysis of fats undergo different oxidative pathways designated as (a), beta (P) and omega (co) pathways. 

Fatty acids undergo beta oxidation in the liver and form acetyl CoA. If acetyl CoA accumulates instead of traversing the citric-acid cycle, the liver becomes more dependent on beta oxidation than on the citric-acid cycle for its source of high-energy phosphate. To continue beta oxidation, coenzyme A is required. If all the CoA is tied up as fatty-acyl CoA and acetyl CoA, no beta oxidation occurs. However, there is a metabolic pathway, unique to the liver, through which to overcome this apparent dilemmaketone-body formation (Fig. 14.3). It occurs as follows in the mitochondrial matrix. 

To some extent this may be subjective, imposing a human interpretation on the observations, but it also reflects an objective reality some reactions carry a greater flux of metabohtes than others, some are active in a wider range of cell types than others, and so on. To understand the entire chart, therefore, it is useful to collect the reactions into groups of transformation sequences known as metabolic pathways. The number of steps considered to be one pathway can be very small if very few steps are needed to convert one important metabolite into another. For example, serine biosynthesis is a three-step pathway, in which the aminoacid serine is synthesized from 3-phosphoglycerate. At the other extreme, beta-oxidation, the process that converts fatty acids from the form in which they are stored in fat cells into the form in which they are metabolically active, involves seven repetitions of the same four types of step, making an unbranched pathway of nearly 30 reactions. 

To further investigate different expression patterns in these three tissues, we subdivided the metabolism TUGs based on substrate classes. Thus, carbohydrate includes all glycoside hydrolases, lipid includes lipases, beta-oxidation enzymes, JH-metabolizing enzymes, etc., and protein includes proteases. TUGs for all subcategories are contributed by all three insects, with the exception of the mevalonate pathway, which is represented only by /. pini (Fig. 3.2). This further supports the observation that their presence in /. pini midguts reflects the pheromone-biosynthetic activity of that tissue. 

Metoprolol is another beta-blocker that is predominantly eliminated by hepatic metabolism [38]. In humans, metoprolol is eliminated by several oxidation pathways, including benzylic hydroxylation (a-hydroxylation), which results in an active metabolite and accounts for 10% of the dose [39]. This pathway is stereoselective for S(—)-metoprolol. The major metabolic pathway, however, is O-demethylation and further oxidation to a carboxylic acid metabolite that accounts for 65% of the dose [38]. O-demethylation favors R(- -)-metoprolol [39] and facilitates the stereoselectivity observed in the plasma concentrations of metoprolol. A third metabolic pathway (N-dealkylation) accounts for < 10% of the dose in humans [39]. 

Beta-oxidation The major metaboiic pathway for oxidising fatty acids, so-caiied because in each cycle it is at the beta-carbon (two along from the carboxyl group linked to CoA) where oxidation occurs. 

Tsemg, K.-Y. Jin, SJ. (1991) J. Biol Chem., 266, 11614-11620, NADPH-dependent reductive metabolism of cis-5 unsaturated fatty acids. A revised pathway for the beta-oxidation of oleic acid. 

Poirier, Y., Antonenkov, V.D, Glumoff, T., and Hiltunen, J.K. (2006) Peroxisomal beta-oxidation - a metabolic pathway with multiple functions. Biochim. Biophys. Acta, 1763, 1413-1426. 

Reiser SE, Mitsky TA, Gruys KJ (2000) Characterization and cloning of an (R)-specific trans-2,3-enoylacyl-CoA hydratase from Rhodospirillum rubrum and use of this enzyme for PHA production in Escherichia coli. Appl Microbiol Biotechnol 53 209-218 Robert J, Marchesini S, Delessert S, Poirier Y (2005) Analysis of the beta-oxidation of tians-unsaturated fatty acid in recombinant Saccharomyces cerevisiae expressing a peroxisomal PHA synthase reveals the involvement of a reductase-dependent pathway. Biochim Biophys Acta 1734 169-177... 

Beta oxidation A metabolic pathway that breaks down fatty acids into 2-carbon pieces. 

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