Enzymatic oxidation, laccase activity

Azinobis(3-ethylbenzothiazoline-6-sulfonic acid), namely ABTS-(NH4)2 (518), is found to be an adequate cosubstrate (or mediator) in the enzymatic oxidation of methyl groups on aromatic rings, lihe mediator (518) acts as a single-electron donor and activator of the enzyme (laccase) but does not function as oxidant of the substrate <9SJOC4320>. 

Parallelism in the specific inhibition of electrocatalytic and enzymatic activity. The specific inhibitors of a particular enzyme are observed also to suppress its electrocatalytic activity in the adsorbed state. Experimental data demonstrate that a,a -dipyridyl completely suppresses the reaction of hydrogen evolution by immobilized hydrogenase fluorine ions inactivate laccase in the reaction of oxygen electroreduction and diphenylhydrazine has the same effect on peroxidase in the reaction of hydrogen peroxide electroreduction. A complete parallelism is also observed in the inactivating effect of hydrogen peroxide on peroxidase in the electrochemical reaction and enzymatic oxidation of o-dianisidine. 

The physical processes of racking and clarification (with bentonite) help remove the enzyme fraction associated with particulate materials (Gortegs and Geisenheim, 1986). In addition, the activity of tyrosinase decreases during yeast fermentation, largely because of the production of ethanol. Consequently, clarified protein-stable wines made from relatively sound berries are unlikely to contain significant quantities of either laccase or tyrosinase and, hence, should undergo little enzymatic oxidation (Simpson, 1980). 

Superoxide anion scavenging activity of the enzymatically synthesized poly(catechin) was evaluated. Poly(catechin), synthesized by HRP catalyst, greatly scavenged superoxide anion in a concentration-dependent manner, and almost completely scavenged at 200 p.M of a catechin unit concentration. The laccase-catalyzed synthesized poly(catechin) also showed excellent antioxidant property. Catechin showed pro-oxidant property in concentrations lower than 300 jlM. These results demonstrated that the enzymatically synthesized poly(catechin) possessed much higher potential for superoxide anion scavenging, compared with intact catechin. 

In some cases, substrates and enzymes are not soluble in the same solvent. To achieve efficient substrate conversion, a large interface between the immiscible fluids has to be established, by the formation of microemulsions or multiple-phase flow that can be conveniently obtained in microfluidic devices. Until now only a couple of examples are published in which a two-phase flow is used for biocatalysis. Goto and coworkers [431] were first to study an enzymatic reaction in a two-phase flow in a microfluidic device, in which the oxidation ofp-chlorophenol by the enzyme laccase (lignin peroxidase) was analyzed (Scheme 4.106). The surface-active enzyme was solubilized in a succinic acid aqueous buffer and the substrate (p-chlorophenol) was dissolved in isooctane. The transformation ofp-chlorophenol occurred mainly at... 

It is now well-established that some enzyme families, including various peroxidases and laccases, catalyze the polymerization of vinyl monomers and other redox active species such as phenol-type structures. Vinyl polymerization by these redox catalysts has recently been reviewed 93). These catalysts have been used to prepare polyanilines 94) and polyphenols 95,96). A few examples of related research are included in this book. For example. Smith et al (57) described a novel reaction catalyzed by horseradish peroxidase (HRP). In the presence of HRP and oxygen, D-glucuronic acid was polymerized to a high molecular weight (60,000) polyether. However, the authors have not yet illucidated the polyether structure. Two other oxidative biotransformations were discussed above i) the sono-enzymatic polymerization of catechol via laccase 31), and ii) the oxidation of aryl silanes via aromatic dioxygenases 30). 

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