Oxidase , aerobic glucose

Berkeley96 investigated oxidase action in preparations obtained from the crystalline style of the mollusc, Saxidomus giganteus. He demonstrated the aerobic and anaerobic production of D-glucosone by separate systems, each of which comprised a component in the style and another in the diatomaceous food of the mollusc. The osone was identified through the formation of D-glucose m-nitrophenylosazone and by reduction with zinc... 

There are many oxidases used in clinical and analytical chemistry for the specific determination of constituents of complex samples, based on the generation of hydrogen peroxide by the action of an aerobic oxidase on its substrate. Cholesterol, glucose, galactose and many other analytes are determined that way. These analyses are also important in food analysis. But the volume of oxidases consumed in food processing is primarily based on the protection afforded the food by the removal of either oxygen or the other substrate acted upon. 

Fig. 4.12 Aerobic oxidation of D-glucose catalyzed by flavin-dependent glucose oxidase.

Hydrogen peroxide is produced industrially by (1) the base/anthraquinone-catalyzed chemical reduction of O2 by water and (2) the palladium-catalyzed hydrogenation of O2. In aerobic biology many oxidases (dehydrogenases) produce HOOH as a biproduct along with oxidized substrate (e.g., glucose oxidase, O2 +... 

Enzymes are often employed in the chemical layer to impart the selectivity needed. We saw an example of this in Chapter 13 when discussing potentiometric enzyme electrodes. An example of an amperometric enzyme electrode is the glucose electrode, illustrated in Figure 15.4. The enzyme glucose oxidase is immobilized in a gel (e.g., acrylamide) and coated on the surface of a platinum wire cathode. The gel also contains a chloride salt and makes contact with silver-silver chloride ring to complete the electrochemical cell. Glucose oxidase enzyme catalyzes the aerobic oxidation of glucose as follows ... 

The reaction rate will be at a maximum at a certain pH, owing to complex acid-base equilibria such as acid dissociation between the substrate, the activated complex, and the products. Also, the maximum rate may depend on the ionic strength and on the type of buffer used. For example, the rate of aerobic oxidation of glucose in the presence of the enzyme glucose oxidase is maximum in an acetate buffer at pH 5.1, but in a phosphate buffer of the same pH, it is decreased. 

The analytical data show that gold catalysis and enzymatic catalysis allow fast and selective aerobic oxidation of glucose according to the same stoichiometry characterized by the formation of hydrogen peroxide as the by-product (Eq. (21.1)) [8]. However, it is not surprising that completely different catalytic systems adopt different reaction mechanisms as shown by the kinetic studies on commercial enzymatic preparations containing /wcose oxidase and catalase [13]. The results of the research support a Michaelis-Menten type mechanism where the kinetic... 

Following an abrupt transition of P. pentosaceum from anaerobic to aerobic metabolism (10 pM O2), the growth rate increases at first, but the formation of acetate from lactate and glucose is slowed down, propionate formation is completely repressed and pyruvate is accumulated in the medium (van Gent-Ruijters et al, 1976 Schwartz et al, 1976). A decrease in the activities of the citric acid cycle enzymes malate dehydrogenase, fumarase and NADH oxidase, lactate oxidase, NADH-dependent fiimarate reductase, lactate-dependent nitrate reductase is observed upon the transition from anaerobic to aerobic (10 pM O2) metabolism (van Gent-Ruijters, 1975). 

Oxidation of different substrates. We found (Vorobjeva, 1959) that glycerol can be used as a sole carbon source by P. jensenii only under aerobic conditions. If fumarate was added to minimal medium, then glycerol fermentation proceeded under anaerobic conditions with fumarate acting as an electron acceptor. Propionibacteria can oxidize compounds more reduced than glycerol, namely, alkanes and long-chain primary alcohols (Table 3.1). Oxidation of hydrocarbons is suppressed by the inhibitors of cytochrome oxidases, NaNa (10 M) and KCN (10" M), respectively, by 88 and 96%, which is similar to the degree of inhibition observed for glucose oxidation by P. pentosaceum. 

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