Other Oxidases

Acyl CoA oxidase, which is induced up to at least 15 X normal levels, catalyzes a specific step characteristic of jl-oxidation in the peroxisome-producing hydrogen peroxide as a byproduct (Fig. 7.10). Other oxidases may also lead to increased hydrogen peroxide. Normally, this is removed and detoxified by the enzyme catalase, which breaks hydrogen peroxide down to water and oxygen. However, catalase is only increased about twofold after treatment with peroxisomal proliferators. 

Mammalian cytochrome oxidase has attracted particular attention. It contains four redox-active transition metal centres, two type a cytochromes (a and a3) and two copper ions. Other oxidases... 

This is found in a range of bacteria,1305 particularly Gram-negative heterotrophic bacteria, and often coexists with other oxidases. The production of cytochrome d occurs under 02-limited or sulfate-limited conditions, and is found in obligate anaerobes. Cytochrome d has a chlorin prosthetic group. It occurs in E. coli as a complex with cytochromes b558 and a,.1322 The complex with cytochrome bsss has been purified.1323... 

Oxygen is the natural electron acceptor from the reduced form of GO, and for any other oxidase. The reduction of oxygen is not without problems. It leads to the degradation of the enzyme by the hydrogen peroxide and the dependency on available oxygen may create interferences in some applications, as has been discussed above. For these reasons, other electron acceptors have been investigated. The idea is to find some way by which the (GO)red could be reoxidized anaerobically, with the ultimate sink for the electrons being the electrode itself (Heller, 1999). 

Concentrations of tyramine and histamine were similar that of angiotonin is estimated. The preparation, which contained active amine oxidase and no other oxidases, was supplied by Karl Folkers of Merck and Company. Data were obtained from C. C. Stock, to whom the author is indebted. 

Oxidase An enzyme requiring molecular O as a substrate to produce water as a reduced product. In the case of cytochrome oxidase, water is the only product of oxygen rednction. With some other oxidases (called mixed fnnction oxidases), one atom of molecular oxygen is converted to water, whereas the other atom of oxygen may be a hydroxylated product. 

Zhou M, Diwu Z, Panchuk-Voloshina N et al (1997) A stable nonfluorescent derivative of resorufin for the fluorometric determination of trace hydrogen peroxide applications in detecting the activity of phagocyte NADPH oxidase and other oxidases. Anal Biochem 253 162-168... 

Other oxidases also derive function from bidirectional PCET pathways at the enzyme active site. The recent crystal structures of PSII [206, 207] support suggestions that as the oxygen evolving complex (OEC) steps through its various S-states [208, 209], substrate derived protons are shuttled to the lumen via a proton exit channel, the headwater of which appears to be the Dgi residue hydrogen-bonded to Mn-bound water [210]. The protons are liberated with the proton-coupled oxidation of the Mn-OH2 site. As shown by the structure reproduced in Fig. 17.23, Dgj is diametrically opposite to Y, which has long been known [148, 151, 152] to be the electron relay between the PS II reaction center and OEC. Notwithstanding,... 

Reducing the 02 concentration around fresh fruits and vegetables reduces their respiration rate to an extent that varies with temperature, commodity, cultivar, and physiological age at harvest. Below a minimum of about 1 to 2% 02, a shift from aerobic to anaerobic respiration occurs with a concomitant increase in CO2 production Q0). The reduction in aerobic metabolism associated with reduced 02 levels is apparently not mediated by cytochrome oxidase, which has a K , value of 10"8 to 10 7 M 02 (11.12). It is more likely that reduction of aerobic respiration results from diminished activity of other oxidases such as ascorbic acid oxidase, polyphenol oxidase (FFO), and glycolic acid oxidase, whose affinities for 02 are 5 to 6 times lower than that of cytochrome oxidase (12). 

Kobayashi and coworkers later evaluated various other oxidases observing efficient polymerization with sarcosine oxidase whereas only little polymerization... 

Co-oxidatioii of carotenoids. A different enzymatic approach for the biotechnological production of Cj 3-compounds uses the carotenoid fraction of plants as aroma precursors. In this case, the cleavage of the carotenoid chain is carried out by "co-oxidation" reactions using lipoxygenase or other oxidase systems. 

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