Oxidase 3-Oxidation

Scheme 2 Simplified catalytic cycle for palladium-catalyzed aerobic oxidation ( oxidase ) reactions...

Electronic spectra provide a simple and convenient way to monitor changes induced in the oxidase by various chemical treatments. Indeed, spectral observations were at the core of the pioneering observations of MacMunn (12), Keilin (96), and Warburg (97) and more recently many investigators have examined the spectra of isolated oxidase, mitochondrial particles, and electron transport particles. The spectra of the fully oxidized [oxidase (IV)] (97a) and the fully reduced [oxidase (0)] oxidase have been well characterized (52) (Table V). In Table VI are spectral parameters for ligand complexes of various oxidation states (98-103). Although the spectra of most of these complexes have been... 

The product C of Fig. 10 could represent the normal form of the fully oxidized oxidase, oxidase (IV). However, experience with hemins suggests that the /t-oxobishemin would form readily—unless the protein provides special conditions that make its formation unfavorable. Clearly, if an... 

Fig. 38. Electron transport in P. aeruginosa, after reference 402. Multiple arrows represent multiple steps, possibly with undetected intermediates. Abbreviations Cu, copper-containing protein Oxid, oxidase enzyme. Dotted arrows indicate side reactions which perhaps are artifacts of extraction.

The spectrum for bovine heart carbonyl heme A in pyridine-bromo-form exhibited a band at 1982 cm a second as yet unexplained weaker band was found at 2080 cm (Figure 10). In Tween 80-phosphate, the buflFer used for the oxidase, a broad band at 1976 cm was obtained for CO heme A (Figure 11). A difference spectrum for CO oxidase vs. oxidized oxidase in 1% Tween 80-0.1M potassium phosphate buffer pH 7.4 at a concentration O.lmM in heme A was obtained (Figure 12). Calcium fluoride cells, path length of 0.025 mm, maintained at 10° zb 2°C were... 

Figure 12, Infrared differ-ence spectrum of carbonyl cytochrome c oxidase vs. oxidized oxidase. Water vapor hand at right used for wavelength calibration. Insert at bottom Soret and visible spectra of the CO derivative in the Cap2 cell used to obtain the infrared spectrum.

The protein cytochrome c oxidase, with a monomeric molecular weight of about 100,000, contains two a-type hemes and two copper atoms. A low-spin ferric heme signal and a so-called intrinsic copper signal near g = 2.0 are observed in the frozen solution EPR spectrum of the fully oxidized oxidase. The latter signal shows EPR features which one could assign either to a thiyl radical (R-S ) or to a cupric ion center with an unusually low g value Since no hf structure from copper is resolved at X- or Q-band frequencies, the controversy could not be solved unambiguously from EPR data alone. 

Oxidoreduciases. Enzymes catalysing redox reactions. The substrate which is oxidized is regarded as the hydrogen donor. This group includes the trivially named enzymes, dehydrogenases, oxidases, reductases, peroxidases, hydrogenases and hydroxylases. 

Figure C1.5.17.(A) Enzymatic cycle of cholesterol oxidase, which catalyses tire oxidation of cholesterol by molecular oxygen. The enzyme s naturally fluorescent FAD active site is first reduced by a cholesterol substrate,...

Tsukihara T, Aoyama H, Yamashita E, Tomizaki T, Yamaguchi H, Shinzawaitoh K, Nakashima R, Yaono R and Yoshikawa S 1995 Structures of metai sites of oxidized bovine heart cytochrome c oxidase at 2.8 angstrom Science 269 1069-74... 

The existence of chaotic oscillations has been documented in a variety of chemical systems. Some of tire earliest observations of chemical chaos have been on biochemical systems like tire peroxidase-oxidase reaction [12] and on tire well known Belousov-Zhabotinskii (BZ) [13] reaction. The BZ reaction is tire Ce-ion-catalyzed oxidation of citric or malonic acid by bromate ion. Early investigations of the BZ reaction used tire teclmiques of dynamical systems tlieory outlined above to document tire existence of chaos in tliis reaction. Apparent chaos in tire BZ reaction was found by Hudson et a] [14] aiid tire data were analysed by Tomita and Tsuda [15] using a return-map metliod. Chaos was confinned in tire BZ reaction carried out in a CSTR by Roux et a] [16, E7] and by Hudson and... 

Figure 11.39 summarizes the reactions taking place in this amperometric sensor. FAD is the oxidized form of flavin adenine nucleotide (the active site of the enzyme glucose oxidase), and FAD1T2 is the active site s reduced form. Note that O2 serves as a mediator, carrying electrons to the electrode. Other mediators, such as Fe(CN)6 , can be used in place of O2. 

Chemical kinetic methods have been applied to the quantitative analysis of a number of enzymes and substrates.One example, is the determination of glucose based on its oxidation by the enzyme glucose oxidase. ... 

Another group of compounds called oxygen scavengers retard oxidation by reducing the available molecular oxygen. Products in this group are water soluble and include erythorbic acid [89-65-6] C HgO, and its salt sodium erythorbate [6381-77-7] C HgO Na, ascorbyl pahnitate [137-66-6] 22 38 7 ascorbic acid [50-81-7] C HgO, glucose oxidase [9001-37-0] and sulfites (23). 

The reactivity of the individual O—P insecticides is determined by the magnitude of the electrophilic character of the phosphoms atom, the strength of the bond P—X, and the steric effects of the substituents. The electrophilic nature of the central P atom is determined by the relative positions of the shared electron pairs, between atoms bonded to phosphoms, and is a function of the relative electronegativities of the two atoms in each bond (P, 2.1 O, 3.5 S, 2.5 N, 3.0 and C, 2.5). Therefore, it is clear that in phosphate esters (P=0) the phosphoms is much more electrophilic and these are more reactive than phosphorothioate esters (P=S). The latter generally are so stable as to be relatively unreactive with AChE. They owe their biological activity to m vivo oxidation by a microsomal oxidase, a reaction that takes place in insect gut and fat body tissues and in the mammalian Hver. A typical example is the oxidation of parathion (61) to paraoxon [311-45-5] (110). 

Xanthine oxidase, mol wt ca 275,000, present in milk, Hver, and intestinal mucosa (131), is required in the cataboHsm of nucleotides. The free bases guanine and hypoxanthine from the nucleotides are converted to uric acid and xanthine in the intermediate. Xanthine oxidase cataly2es oxidation of hypoxanthine to xanthine and xanthine to uric acid. In these processes and in the oxidations cataly2ed by aldehyde oxidase, molecular oxygen is reduced to H2O2 (133). Xanthine oxidase is also involved in iron metaboHsm. Release of iron from ferritin requires reduction of Fe " to Fe " and reduced xanthine oxidase participates in this conversion (133). 

Histamine AND histamine antagonists). It is formed from histidine by the enzyme L-histidine decarboxylase. In the periphery, histamine is stored ia mast cells, basophils, cells of the gastric mucosa, and epidermal cells. In the CNS, histamine is released from nerve cells and acts as a neurotransmitter. The actions of histamine ate terrninated by methylation and subsequent oxidation via the enzymes histamine-/V-methyltransferase and monoamine oxidase. 

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