Enzymatically generated

If the luciferase sample solution contains a flavin-reductase, luciferase activity can be measured by the addition of FMN and NADH, instead of FMNH2. In this case, the turnover of luciferase takes place repeatedly using the FMNH2 that is enzymatically generated thus, the luminescence reaction continues until aldehyde or NADH is exhausted. A crude luciferase extracted from luminous bacteria usually contains a flavin-reductase. 

Figure 10.19 Oxidative enzymatic generation of dihydroxyacetone phosphate in situ for stereoselective aldol reactions using DHAP aldolases (a), and extension by pH-controlled, integrated precursor preparation and product liberation (b).

Scheme 3.7 Electrochemical or enzymatic generation of NO from cupferron.

Other postulated routes (Jourd heuil et al., 2003) to RSNO formation include the reaction between NO and 02 to yield N02 via a second-order reaction. NO and thiolate anion, RS, react giving rise to thiyl radical, (RS ) [e]. RS then reacts with NO to yield RSNO [f]. The reaction between RS and RS- can also be the source of non-enzymatic generation of superoxide anion (02 ) [g], [h]. 02 reacts with NO to produce peroxynitrite (ONOO ) [i] (Szabo, 2003). Thiols react with ONOOH to form RSNOs [k] (van der Vliet et al.,1998). 

Lins, R. J. Flitsch, S. L. Turner, N. J. Irving, E. Brown, S. A. Enzymatic generation and in situ screening of a dynamic combinatorial library of sialic acid analogues. Angew. Chem. Int. Ed. 2002, 41, 3405-3407. 

The electrophilic primary and secondary quinones undergo addition of nucleophiles, including flavonoids. For instance, nucleophilic addition of catechin to its enzymatically generated quinone yielded a catechin dimer in which the catechin moieties are linked through a C6 C8 biphenyl linkage. This B-type dehydrodicatechin further oxidized to yellow pigments. Additional dehydrodicatechins arise from radical coupling of the catechin semi-quinones formed by retro-disproportionation, in which the catechin moieties are linked... 

Popular EPR-based assays of antioxidant activity include the DPPH assay, in which the ability of compounds to quench (by H-atom transfer) the 1,1-diphenyl-2-picrylhydrazyl radical is used to rank their antioxidant activity. This method has been applied widely to the analysis of dietary antioxidants and extracts from medicinal plants.213 219 Extensive use has also been made of assays based on the competition between spin traps and test compounds for reaction with enzymatically-generated 02 and, in the presence of a metal catalyst, the OH rad-... 

Lipid peroxidation has often been regarded simply as an undesirable side reaction, but it is also a normal part of metabolism. Initiated by enzymatically generated radicals, peroxidation occurs as specific metabolic pathways, such as the arachidonate cascade, which leads to a variety of local hormones and other substances (Eq. 21-16).254 2563... 

It should be stressed that it is a prerequisite of successful flavor precursor studies that the contribution of the odorant under investigation to a food flavor or off-flavor has been established. Sometimes the structure of a precursor can be assumed on the basis of structural elements in the odorant. In such cases, additions of the respective isotope-labelled precursor to the food system is commonly used to elucidate the precursor and to clarify reaction pathways governing the formation of the odorant. This method has been frequently applied, especially, in studies on the enzymatic generation of odor-active aldehydes (e.g., (Z)-3-hexenal in tea leaves) or alcohols (e.g., l-octen-3-oI in mushrooms) [cf. reviews in 84, 85] as well as lactones [86] from unsaturated fatty acids. 

Fig. 18.7. Schematic representation of the immobilization of the biotinylated cholera toxin B subunit using the biotin-avidin bridging system. The hydrophilic co-polymer on the transducer surface improves the permeation of the enzymatically generated quinone.

IgG (mouse) Sandwich immunoassay using SPCE-surface-immobilised anti-IgG antibody FLA amperometric, reduction of enzymatically generated iodine o.ov 30-700 ngmU1 3 ngmU1 Gao et al. [81]... 

Phosphate is detected via the immobilised PyOD which converts it in the presence of pyruvate and oxygen to hydrogen peroxide, carbon dioxide and acetylphosphate (Eq. (23.6)). The enzymatically generated hydrogen peroxide can then be monitored at +420 mV vs. Ag/AgCl ... 

The amperometric response, described above, is based on the electrooxidation at the platinum-modified electrode of the enzymatically generated hydrogen peroxide at + 0.60 V vs. Ag/AgCl. 

The HRP-immunosensors are potentiostated at —0.1V vs. SCE to detect the enzymatically generated label. 

The PPO-B-immunosensors are potentiostated at —0.2 V vs. SCE in order to reduce the enzymatically generated o-quinone. 

As a final example in this series of alkaloids, the enantio-selective synthesis of (+)-tacamonine is illustrated, which is also based on enzymatic generation of a chiral lactone related to the approaches described above. 

Kristensen JB, Olsen SM, Laursen BS et al. (2010) Enzymatic generation of hydrogen peroxide shows promising antifouling effect. Biofouling 26 141-153... 

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