Hydroxy-, enzymic oxidation

This enzyme [EC 1.14.15.1], also known as camphor 5-exo-methylene hydroxylase, and cytochrome P450-cam, catalyzes the reaction of (+)-camphor with putidare-doxin and dioxygen to generate (-F)-exo-5-hydroxy-camphor, oxidized putidaredoxin, and water. A heme-thiolate acts as a cofactor. The enzyme can also utilize ( )-camphor as a substrate, and l,2A-campholide will result in the formation of 5-exo-hydroxy-l,2-campholide. V. Ullrich W. Duppel (1975) The Enzymes, 3rd ed., 12, 253. 

The mechanism of flavin reduction in b2 has been a topic of debate for decades. Soon after it was discovered that DAAO could catalyze the elimination of Cl from chlorinated substrates, very similar experiments were conducted with many a-hydroxy acid oxidizing enzymes, including F 2- However, HCl elimination was not observed when using 3-Cl-lactate as a substrate. Studies using 3-Br-pynivate as an electron acceptor for lactate oxidation were interpreted as evidence of a carbanion mechanism of flavin reduction. ... 

LMO from Mycobacterium smegmatis is the best-studied example of this enzyme. The enzyme is an octomer of identical subunits, with one FMN per monomer. Even though no structural information has been obtained for LMO, much can be inferred from the high similarity of LMO to other ct-hydroxy acid oxidizing flavoenzymes. LMO exhibits many common properties of flavoprotein oxidases. It makes an N5 sulfite adduct and stabilizes anionic semiquinone and the benzoquinoid form of 8-mercapto-FMN," all of which are explained by the presence of a positive charge in the protein at the Nl—C2=0 locus. Sequence... 

L-lactate oxidase (LOX) catalyzes the oxidation of L-lactate to pyruvate with the concomitant reduction of the enzyme-hound FMN. The reduced enzyme is oxidized hy molecular oxygen resulting in oxidized enzyme and H207- LOX has substantial sequence homology to other a-hydroxy acid oxidizing flavoproteins, containing all the residues thought to he important for catalysis in this class of enzymes/... 

A contrasting mode of flavoprotein reactivity with an acetylenic inactivator occurs in the reaction of 2-hydroxy-3-butynoate (13, Fig. 15) with a number of a-hydroxy acid oxidizing enzymes. This process is exemplified by the inactivation of L-lactate oxidase from Mycobacterium smegmatis, an enzyme which catalyzes the oxidative decarboxylation of lactate to yield acetate, carbon dioxide, and water (Walsh, 1979, p. 408). Incubation of 13 with lactate oxidase leads to inactivation of the enzyme with a partition ratio that varies from 110 in the... 

The electrochemical (and chemical and enzymic) oxidation of 7-hydroxychlorpromazine leads to the eventual formation of 7,8-dioxochlor-promazine which, according to the mechanism proposed by Neptune and McCreery, " proceeds through a trihydroxylated intermediate (VI, Figure 10). It has been suggested " that the oxidized form of the latter compound (i.e., VII, Figure 10) could react with neuromembrane proteins, particularly at thiol sites, in the same way described for the p-quinone of 6-hydroxy-dopamine (see p. 143) and hence cause some neurophysiological effect. 

Unsaturated oils often contain small amounts of hydroxy and/or epoxy acids after prolonged storage, probably as a result of enzymic and/or non-enzymic oxidation (Sections 10.2 and 10.3). 

Wong and Matos (1985) reported a stereospecific oxidation of 1,2--diols to a-hydroxy carboxylic acids via a-hydroxy aldehydes.. The trick employed here is to coimmobilize HLADH and aldehyde dehydrogenase (AldDH) into polyacrylamide. The former enzyme oxidizes the diol to the corresponding a-hydroxy aldehyde, which is further oxidized to the a-hydroxy carboxylic acid by the latter enzyme (Scheme 34). After 40 % conversion of the substrates, enantiomer... 

Compound 66 was isolated in low yield and the quinoneimide, 67, was trapped by starting material, 65, as a 1,2-di(p-hydroxybenzyl)-tetrahydroisoquinoline. The reaction does not take place when the nitrogen is acylated or when the hydroxy group is methylated. It is of interest that the same reaction takes place in enzyme oxidations of similar materials (63) and in mass spectral fragmentations. Such reactions have not been noted in chemical oxidation, although it is questionable whether they have been looked for carefully. 

Blaschko, H. and Levine, W. G., Enzymic oxidation of psilocine and other hydroxy-indoles, Biochem. Pharmacol. 3, 168 (1960). 

L-Amino acid oxidase of rat kidney appears to catalyze the same type of reaction as n-amino acid oxidase. It oxidizes the monoamino, mono-carboxylic acids, but does not attack either dicarboxylic or polybasic compounds. Proline and W-methylamino adds are oxidized. A unique property of this enzyme is its ability to oxidize hydroxy acids. Only L-hydroxy acids are attacked. The ratio of hydroxy acid oxidation rate to amino acid rate is constant throughout purification. In general, hydroxy acid oxidation proceeds somewhat more rapidly than amino add oxidation, and the hydroxy acids corresponding to the basic amino adds... 

Knowledge of hydroxyproline oxidation is even more advanced than that for proline. Formation of a carbonyl compound on enzymic oxidation of L-hydroxyproline had been observed by Taggart and Krakaur 173), and it was postulated to be y-hydroxyglutamic-y-semialdehyde in equilibrium with A -pyrroline-3-hydroxy-5-carboxylic acid. 

Graveland has shown that in the enzymic oxidation of linoleic acid in doughs and in flour-water suspensions the products include two isomeric hydroperoxy-acids, two isomeric hydroxy-acids, two isomeric hydroxy-epoxy-octadecenoic acids, and some trihydroxy-octadecenoic acids. 

Ketone body synthesis occurs only in the mitochondrial matrix. The reactions responsible for the formation of ketone bodies are shown in Figure 24.28. The first reaction—the condensation of two molecules of acetyl-CoA to form acetoacetyl-CoA—is catalyzed by thiolase, which is also known as acetoacetyl-CoA thiolase or acetyl-CoA acetyltransferase. This is the same enzyme that carries out the thiolase reaction in /3-oxidation, but here it runs in reverse. The second reaction adds another molecule of acetyl-CoA to give (i-hydroxy-(i-methyl-glutaryl-CoA, commonly abbreviated HMG-CoA. These two mitochondrial matrix reactions are analogous to the first two steps in cholesterol biosynthesis, a cytosolic process, as we shall see in Chapter 25. HMG-CoA is converted to acetoacetate and acetyl-CoA by the action of HMG-CoA lyase in a mixed aldol-Claisen ester cleavage reaction. This reaction is mechanistically similar to the reverse of the citrate synthase reaction in the TCA cycle. A membrane-bound enzyme, /3-hydroxybutyrate dehydrogenase, then can reduce acetoacetate to /3-hydroxybutyrate. 

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