Hydrogen peroxide, enzymatic degradation

An experimental set-up such as that depicted in Fig. 5.12.C was also used by Nieman s group for the determination of free and total cholesterol in serum [37]. A solution of the enzyme (cholesterol oxidase) at pH 7 was forced through a microporous membrane. The pH gradient across the membrane (from 7 to 9) facilitated the enzymatic degradation of the analyte and subsequent diffusion of the hydrogen peroxide formed to the PMT in the reagent/sample stream in order to react with luminol in the presence of horseradish peroxidase as the catalyst at pH 9 —the copper chelate commonly used as catalyst for this purpose requires pH 11. The system per-... 

All three chloroacetic acids (chloroacetic acid [MCA], dichloroacetic acid [DCA], and trichloroacetic acid [TCA]) are naturally occurring (7), with TCA being identified in the environment most frequently (reviews (278, 405 108)). However, these chlorinated acetic acids also have anthropogenic sources. The major source of natural TCA appears to be the enzymatic (chloroperoxidase) or abiotic degradation of humic and fulvic acids, which ultimately leads to chloroform and TCA. Early studies (409) and subsequent work confirm both a biogenic and an abiotic pathway. Model experiments with soil humic and fulvic acids, chloroperoxidase, chloride, and hydrogen peroxide show the formation of TCA, chloroform, and other chlorinated compounds (317, 410-412). Other studies reveal an abiotic source of TCA (412, 413). 

The determination of the purine-nucleotide metabolites xanthine, hypox-an thine, and inosine by biosensors is of special interest for the estimation of meat or fish freshness. After the death of a fish, adenosine triphosphate (ATP) in the fish tissue is quickly degraded to inosine monophosphate (IMP). Further enzymatic decomposition of IMP leads to the accumulation of hypoxan thine (Hx), which is used as an indicator of fish freshness. To quantify these compounds with biosensors, it is possible to perform amperometric measurements of the generated hydrogen peroxide or the consumed oxygen according to the following enzymatic reactions ... 

Most of the hydrogen peroxide is decomposed by catalytic degradation (platinum ring) chemical neutralization using pyruvate, sodium bisulfite, or sodium thiosulfate dilution and rinsing and enzymatic neutralization (catalase). 

The numbers of living cells in water can be sufficiently reduced by the addition of 1% of a 3% hydrogen peroxide solution. Heavily contaminated products, e.g. water based paints and thickener solutions showing signs of viscosity loss due to enzymatic degradation may be saved by the addition of 0 05-0 1% of a 30% hydrogen peroxide solution with stirring. After 24 h, when microbes and enzymes are inactivated and most of the unpleasant odours are eliminated by oxidation, the viscosity of the material is restored with additional thickener and the in-can/ in-tank protection by the incorporation of a suitable preservative. 

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