A oxidation, enzymic

Schneider S, G Fuchs (1998) Phenylacetyl-CoA acceptor oxidoreductase, a new a-oxidizing enzyme that produces phenylglyoxylate. Assay, membrane localization, and differential production in Thauera aro-matica. Arch Microbiol 169 509-516. 

Fig. 15. EPR spectra for galactose oxidase complexes, (a) Oxidized enzyme (AGO) prepared by treating native galactose oxidase with K3Fe(CN)0. (b) Radical-free lAGO complex, prepared by treating native galactose oxidase with K4Fe(CN)0. Instrumental parameters microwave power, 10 [xW microwave frequency, 9.223 GHz modulation amplitude, 5 G temperature, 30 K.

System A oxidative enzyme L-lactate dehydrogenase reducing system electrochemical reduction... 

Fia. 20. Absorption spectra of the purified NADH dehydrogenase of C. uliUs at 0.8 mg/ml. Trace (a), oxidized enzyme trace (b) after addition of 0.1 mAf NADH inset, (b) minus (a). From Tottmar and Ragan (ISS). 

The mitochondrial system uses acetyl-CoA, not malonyl-CoA, by a slightly modified reversal of j6-oxidation. The substrates are saturated and unsaturated Ci2, Ci4, and Ci6 fatty acids, and the products are Cig, C20, C22, and C24 fatty acids. The first reduction step utilizes NADH, and the enzyme is /5-hydroxyacyl dehydrogenase (a -oxidation enzyme) the second reduction step utilizes NADPH, and the enzyme is enoyl reductase. 

The aim of the present study has been to purify and characterize the a-oxidation enzyme system in cucumber using fatty acid analogues with a sulphur atom at different positions in the carbon chain as substrates. 

Phytanic acid Refsum s disease a-Oxidation enzymes Chronic polyneuropathy night-blindness narrowing of visual field skeletal malformation... 

Oxidative Reactions. The majority of pesticides, or pesticide products, are susceptible to some form of attack by oxidative enzymes. For more persistent pesticides, oxidation is frequently the primary mode of metaboHsm, although there are important exceptions, eg, DDT. For less persistent pesticides, oxidation may play a relatively minor role, or be the first reaction ia a metaboHc pathway. Oxidation generally results ia degradation of the parent molecule. However, attack by certain oxidative enzymes (phenol oxidases) can result ia the condensation or polymerization of the parent molecules this phenomenon is referred to as oxidative coupling (16). Examples of some important oxidative reactions are ether cleavage, alkyl-hydroxylation, aryl-hydroxylation, AJ-dealkylation, and sulfoxidation. 

An important function of certain carotenoids is their provitamin A activity. Vitamin A may be considered as having the stmcture of half of the P-carotene molecule with a molecule of water added at the end position. In general, all carotenoids containing a single unsubstituted P carotene half have provitamin A activity, but only about half the activity of P carotene. Provitamin A compounds are converted to Vitamin A by an oxidative enzyme system present in the intestinal mucosa of animals and humans. This conversion apparendy does not occur in plants (see Vitamins, VITAMIN a). 

Riboflavin was first isolated from whey in 1879 by Blyth, and the structure was determined by Kuhn and coworkers in 1933. For the structure determination, this group isolated 30 mg of pure riboflavin from the whites of about 10,000 eggs. The discovery of the actions of riboflavin in biological systems arose from the work of Otto Warburg in Germany and Hugo Theorell in Sweden, both of whom identified yellow substances bound to a yeast enzyme involved in the oxidation of pyridine nucleotides. Theorell showed that riboflavin 5 -phosphate was the source of the yellow color in this old yellow enzyme. By 1938, Warburg had identified FAD, the second common form of riboflavin, as the coenzyme in D-amino acid oxidase, another yellow protein. Riboflavin deficiencies are not at all common. Humans require only about 2 mg per day, and the vitamin is prevalent in many foods. This vitamin... 

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... 

Conjugation is crucial not only for the colors we see in organic molecules but also for the light-sensitive molecules on which our visual system is based. The key substance for vision is dietary /3-carotene, which is converted to vitamin A by enzymes in the liver, oxidized to an aldehyde called 11-frans-retinal, and then isomerized by a change in geometry of the C11-C12 double bond to produce 11-cis-retinal. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

Alcohol dehydrogenase is a cytoplasmic enzyme mainly found in the liver, but also in the stomach. The enzyme accomplishes the first step of ethanol metabolism, oxidation to acetaldehyde, which is further metabolized by aldehyde dehydrogenase. Quantitatively, the oxidation of ethanol is more or less independent of the blood concentration and constant with time, i.e. it follows zero-order kinetics (pharmacokinetics). On average, a 70-kg person oxidizes about 10 ml of ethanol per hour. 

The findings discussed above suggest that the presence of Met(O) residues in a-l-PI and lens proteins might account for some of the observed clinical manifestations. It is of interest to speculate that Met(0)-peptide reductase may function as a repair enzyme to prevent the accumulation of Met(O) residues in most proteins. Whether in those examples as discussed above, the accumulation of Met(O) in proteins is a result of an overwhelming increase in the synthesis of biological oxidants and/or a decrease in the ability to either destroy the biological oxidants or reduce the Met(O) residues in the proteins is not known. If it is the latter, this could be due to a decrease in the reductase itself or to some impairment in the reducing system that the enzyme requires. 

Uchicda, Y., Izai, K., Orii, T., Hashimoto, T. (1992). Novel fatty acid p-oxidation enzymes in rat liver mitochondria. II. Purification and properties of enoyl-coenzyme A (CoA) hydratase/3-hy-droxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase trifunctional protein. J. Biol. Chem. 267, 1034-1041. 

Catalase is a hver enzyme that uses hydrogen peroxide to oxidize other substances. In vivo, the catalase system does not play a significant role in ethanol metabolism, probably because the quantities of hydrogen peroxide available are insufficient for ethanol metabolism. 

An important advance on these studies was the possibility of isolating AORs from Fe enriched media with obvious interest for an iron-sulfur center site labeling, with enhanced sensitivity of the Mossbauer studies. The work developed with bacterial systems is advantageous as compared with mammalian systems for isotopic labeling and opens the possibility of a direct measurement of substrate binding. Spectra of the enzyme in oxidized, partially reduced, benzaldehyde-reacted, and fully reduced states were recorded at different temperatures and with variable externally applied magnetic fields (222). In the oxidized enzyme, the clusters are diamag-... 

The reduced NADH of the tespitatoty chain is in turn oxidized by a metalloflavoptotein enzyme—NADH dehydrogenase. This enzyme contains FeS and FMN, is tighdy bound to the tespitatoty chain, and passes te-ducing equivalents on to Q. 

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