Enzymes enzymic oxidation

Oxidative substitutions at ring junction positions in various tetrahydro-5-deaza-pterins (79JA6068) and -flavins (77JA6721) have been studied, e.g. to give (13), and the oxidation-reduction reactions of 5-deazaflavins (e.g. 78CL1177, 80CPB3514) across the 1,5-positions, e.g. (19) (20), are involved in their co-enzymic role in enzymic oxidations (see Section... 

Enzymic oxidations at the 7-position of pyrido[2,3-oxygenated derivatives and of the 8-N-oxide have been observed in the metabolism of the pyrido[2,3-e/]pyrimidine analogues of the antiepileptic drug methaqualone (75MI21502, 74MI21500). 

A -Pyrroline has been prepared in low yield by oxidation of proline with sodium hypochlorite (71), persulfate (102), and periodate (103). A -Pyrroline and A -piperideine are products of enzymic oxidation via deamination of putrescine and cadaverine or ornithine and lysine, respectively (104,105). This process plays an important part in metabolism and in the biosynthesis of various heterocyclic compounds, especially of alkaloids. 

Meyer, O. Fiebig, K. Enzymes Oxidizing Carbon Monoxide D. Reidel Dordrecht, The Netherlands, 1985. 

Peroxidation is also catalyzed in vivo by heme compounds and by lipoxygenases found in platelets and leukocytes. Other products of auto-oxidation or enzymic oxidation of physiologic significance include oxysterols (formed from cholesterol) and isoprostanes (prostanoids). 

D. Craig and S. A. Holditch. The degradation of hydroxypropyl guar fracturing fluids by enzyme, oxidative, and catalyzed oxidative breakers Pt 2 Crosslinked hydroxypropyl guar gels Topical report (January-April 1992). Gas Res Inst Rep GRI-93/04192, Gas Res Inst, December 1993. 

Aside from China, Japan, North Africa, and the Middle East, most tea is consumed as black tea, which is produced by promoting the enzymic oxidation of tea flavanols. For the production of green tea, inactivation of the tea enzyme system by rapid firing is carried out to prevent flavanol... 

The origin of many of the components of black tea aroma has been studied. Aldehydes are produced by catechin quinone oxidation of amino acids. Enzymic oxidation of carotenoids during manufacture generates ionones and their secondary oxidation products such as theaspirone and dihydroactinidolide. Oxidation of linoleic acid is responsible for the formation of trans-2-hexenal.82... 

Roberts, E. A. H., The phenolic substances of manufactured tea. II. Their origin as enzymic oxidation products in fermentaiton. J. Sci. Food Agri., 9 212, 1958. 

Kiener, A. (1992) Enzymic oxidation of methyl groups in heteroarenes a versatile method for the preparation of heteroaromatic carborylic acids. Angewandte Chemie-International Edition, 31 (6), 774—775. 

Arnstein and Bentley believed that the direct conversion of glucose (XXII) might proceed by the following sequence enzymic oxidation of... 

Klein and Olsen126 studied the action of kojic acid on the enzymic oxidation of amino acids by the liver and kidney of rats. Low concentrations of kojic acid in vitro inhibited the oxidation of a number of D-amino acids, L-phenylalanine, and a few related compounds. Kojic acid was found to compete with D-amino acid oxidase for the substrate. 

Cabanes J, Sanchez-Ferrer A, Bru R and Garcia-Carmona F. 1988. Chemical and enzymic oxidation by tyrosinase of 3,4-dihydroxymandelate. Biochem J 256 681—684. 

Abiotic spoilage is produced by different physical and chemical changes such as hydrolytic action of enzymes, oxidation of fats, breakdown of proteins, and a browning reaction between proteins and sugars. However, in this chapter we focus on microbial deterioration and their effects on bioactive compounds. 

Biddle and Wehry [429] carried out fluorometric determination of manganese II in seawater via catalysed enzymic oxidation of 2,3-diketogluconate. The detection limit was 8 pmoll-1 Mn (II). 

This enzyme oxidizes a- and P-anomers of D-glucose to the same extent and shows excellent stability and sensitivity about twice that for the methods with immobilized glucose oxidase. In this approach, pyranose oxidase is immobilized on tresylate-poly(vinylalcohol) beads and packed into a stainless column and peroxidase is immobilized on tresylate-hydrophylic vinyl polymer beads and packed into a transparent FITE tube that is used as the CL flow cell. The H202... 

In accord with this mechanism, free peroxyl radical of the reaction product hydroperoxide activates the inactive ferrous form of enzyme (Reaction (1)). Then, active ferric enzyme oxidizes substrate to form a bound substrate radical, which reacts with dioxygen (Reaction (4)). The bound peroxyl radical may again oxidize ferrous enzyme, completing redox cycling, or dissociate and abstract a hydrogen atom from substrate (Reaction (6)). 

Since the oxidative polymerization of phenols is the industrial process used to produce poly(phenyleneoxide)s (Scheme 4), the application of polymer catalysts may well be of interest. Furthermore, enzymic, oxidative polymerization of phenols is an important pathway in biosynthesis. For example, black pigment of animal kingdom "melanin" is the polymeric product of 2,6-dihydroxyindole which is the oxidative product of tyrosine, catalyzed by copper enzyme "tyrosinase". In plants "lignin" is the natural polymer of phenols, such as coniferyl alcohol 2 and sinapyl alcohol 3. Tyrosinase contains four Cu ions in cataly-tically active site which are considered to act cooperatively. These Cu ions are presumed to be surrounded by the non-polar apoprotein, and their reactivities in substitution and redox reactions are controlled by the environmental protein. 

Prostate Citric acid Acid phosphatase Spermidine Zinc ions Calcium ions Proteolytic enzymes Oxidation generates ATP and removes protons (Chapter 6) Hydrolyses phosphatidylcholine Not known Helps to stabilise structure of DNA (see Table 15.4) Stimulate coagulatiou of semeu in vagina Gradual breakdowu of coagulum to release sperm... 

It has been demonstrated that Mn is the preferred substrate for MnP (13-17). The enzyme oxidizes Mn to Mn and the Mn produced, complexed with a suitable carboxylic acid ligand (12-16), diffuses from the enzyme and in turn oxidizes the organic substrates (6,8,13-17). Thus the Mn ion participates in the reaction as a diffusible redox couple (Fig. 1) rather than as an enzyme-binding activator. In support of this concept, we have demonstrated that chemically prepared Mn complexed with a carboxylic acid ligand such as malonate or lactate mimics the reactivity of the enzyme (6,8,14,15). 

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