Reduction, biological enzymatic

Reductive Reactions. A number of pesticides are susceptible to reductive reactions under anaerobic conditions, depending on the substituents present on the molecule. Reductive reactions can be either chemically or enzymatically mediated. Because biologically generated reductants, eg, cysteine and porphyrins, are frequendy the electron donors for both chemical and enzymatic reactions, results from sterile controls are not necessarily conclusive in distinguishing between the two mechanisms. The only definitive means of distinguishing between chemical vs biological (enzymatic) reactions is to determine whether the reaction rate is consistent with enzyme kinetics. The most common reductive reactions are the reduction of nitro substituents and reductive dechlorination. 

Excellent biological arguments exist for a direct impact of fever specifically on neurological outcome. On a local level, fever produces increased levels of excitatory amino acids (e.g., glutamate and dopamine), free radicals, lactic acid, and pyr-uvate. There is an increase in cell depolarizations and BBB breakdown. Enzymatic function is impaired and cytoskeletal stability reduced. These events lead to increased cerebral edema, with a possible reduction in CPP as well as larger volumes of ischemic injury. " ... 

Weissbach, H. and Brot, N. (1981). Enzymatic reduction of oxidised alpha-l-proteinase inhibitor restores biological activity. Proc. Natl Acad. Sci. USA, 78, 7483—7486. 

Anaerobic bio-reduction of azo dye is a nonspecific and presumably extracellular process and comprises of three different mechanisms by researchers (Fig. 1), including the direct enzymatic reduction, indirect/mediated reduction, and chemical reduction. A direct enzymatic reaction or a mediated/indirect reaction is catalyzed by biologically regenerated enzyme cofactors or other electron carriers. Moreover, azo dye chemical reduction can result from purely chemical reactions with biogenic bulk reductants like sulfide. These azo dye reduction mechanisms have been shown to be greatly accelerated by the addition of many redox-mediating compounds, such as anthraquinone-sulfonate (AQS) and anthraquinone-disulfonate (AQDS) [13-15],... 

As discussed earlier, Azo biological decolorization are mainly reduced in a direct reduction or mediated/indirect reduction with nonspecial azo reductase or reduced enzyme cofactors (Figs. 1 and 3). According to the direct enzymatic reduction mechanism, nonspecial azo reductase can catalyze the transfer of reducing equivalents originating from the oxidation of original electron donor in the azo dyes. In... 

The acceleration mechanism of redox mediators are presumed by van der Zee [15]. Redox mediators as reductase or coenzymes catalyze reactions by lowering the activation energy of the total reaction. Redox mediators, for example, artificial redox mediators such as AQDS, can accelerate both direct enzymatic reduction and mediated/indirect biological azo dye reduction (Fig. 3). In the case of direct enzymatic azo dye reduction, the accelerating effect of redox mediator will be due to redox mediator enzymatic reduction in addition to enzymatic reduction of the azo dye. Possibly, both reactions will be catalyzed by the same nonspecific periplasmic enzymes. In the case of azo dye reduction by reduced enzyme cofactors, the accelerating effect of redox mediator will either be due to an electron shuttle between the reduced enzyme cofactor and redox mediator or be due to redox mediator enzymatic reduction in addition to enzymatic reduction of the coenzymes. In the latter case, the addition of redox mediator simply increases the pool of electron carriers. 

Despite intense study of the chemical reactivity of the inorganic NO donor SNP with a number of electrophiles and nucleophiles (in particular thiols), the mechanism of NO release from this drug also remains incompletely understood. In biological systems, both enzymatic and non-enzymatic pathways appear to be involved [28]. Nitric oxide release is thought to be preceded by a one-electron reduction step followed by release of cyanide, and an inner-sphere charge transfer reaction between the ni-trosonium ion (NO+) and the ferrous iron (Fe2+). Upon addition of SNP to tissues, formation of iron nitrosyl complexes, which are in equilibrium with S-nitrosothiols, has been observed. A membrane-bound enzyme may be involved in the generation of NO from SNP in vascular tissue [35], but the exact nature of this reducing activity is unknown. 

Biotransformations of morphinan alkaloids have been reported for plant, fungal, and mammalian enzymatic systems with emphasis on rather specific reactions such as the reduction of ketones, N- and O-demethylation, and perox-idative transformations. Furuya et al. used immobilized tissue culture cells of Papaver somniferum to accomplish the selective reduction of codeinone (135) to codeine (136) (207) (Scheme 30). Suspension cultures of a well-established cell line of P. somniferum were grown for one week as a source of cell mass for immobilization in calcium alginate. The cells continued to live in the alginate matrix for 6 months maintaining their biological activity. The reduction of co-... 

Since HA is unstable in vivo , and is known to rapidly associate with the heme part of heme proteins , and possibly also with a variety of biological oxidants, such as the superoxide anion that is produced by many mammalian cells, it is difficult to demonstrate its accumulation in vivo. Already in 1932 Lindsey and Rhines discussed some analytical difficulties in the detection of HA, since when added externally, it disappeared rapidly from bacterial cultures this led to the conclusion that even if it is produced as an intermediate, its consumption is too fast to allow the accumulation of sufficient quantities for analytical demonstration. Compelling indirect evidence for the presence of HA as an intermediate in the enzymatically catalyzed reduction of nitrite (N02 ) to NH3 was provided by Einsle and colleagues , who characterized the crystal structure of the complex obtained by soaking cytochrome c-nitrite reductase with NH20H. ... 

Verschraagen, M., Boven, E., Torun, E., Hausheer, F. H., Bast, A., and van der Vijgh, W. J. F., Possible (enzymatic) routes and biological sites for metabohc reduction of BNP7787, a new protector against cisplatin-induced side-effects. Biochemical Pharmacology 68(3), 493-502, 2004. 

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