Aerobic rate determining step

Probably the major problem in the scale-np of fermentation processes lies in maintaining aeration efficiency to aerobic cultnres. Aeration is normally achieved by sparging with air and the rate determining step in a non-viscons fermentation is the... 

A new catalytic system consisting of a persistent macrocyclic aminoxyl radical and the couple Mn(N03)2-Co(NC>3)2 for the aerobic oxidation of alcohols to carbonyl compounds has been developed. The rate-determining step has been identified by studying the effect of substituents on the oxidation of benzyl alcohol. The chemistry of aminoxyl, amidoxyl, and imidoxyl radicals has been discussed.265... 

The stopped-flow kinetics of the anaerobic reactions were also studied. Reaction of linoleic acid with the yellow or purple enzymes results in (1) hydrogen abstraction, (2) formation of the radical L- (hence products of the anaerobic reactions), and (3) bleaching of the colored enzymes to Fe(II) species (fcg and k steps). Thus the rate of hydrogen abstraction (Ag and Ag) was measured as the rate of bleaching of the colored enzymes and found to be faster than Aj—formation of the yellow enzyme. This indicates that, in the presence of linoleic acid, the enzyme remains largely in the ferrous state (native enzyme) and that, unlike the situation in the aerobic reaction, hydrogen abstraction is not the rate-determining step in the anaerobic reaction. 

Further research into the reaction mechanism revealed that the reaction rate was correlated with the electron structure of the sulfoxide the more electropositive sulfoxides were the better oxygen donors. Excellent correlation of the reaction rates with the heterolytic benzylic carbon-hydrogen bond dissociation energies indicated a hydride abstraction mechanism in the rate-determining step to yield a carbocation intermediate. The formation of 9-phenylfluorene as by-product in the oxidation of triphenylmethane supports this suggestion. Further kinetic experiments and NMR showed the formation of a polyoxometalate-sulfoxide complex before the oxidation reaction, this complex being the active oxidant in these systems. Subsequently, in a similar reaction system, sulfoxides were used to facilitate the aerobic oxidation of alcohols [29]. In this manner, benzylic, allyUc, and aliphatic alcohols were all oxidized to aldehydes and ketones in a reaction catalyzed by Ke jn-type... 

KIE and the influence of substituents have been determined for the decomposition of benzyl nitrite, a key intermediate in the nitric-acid-mediated aerobic oxidation of benzyl alcohol. The differences in the reactivities of the substituted benzyl nitrites are reflected in the oxidation of the corresponding alcohols and also affect the rate-determining step in the overall mechanism. ... 

By means of stopped-flow spectrophotometry, the reaction of flavopapain IV withN-benzyl-l,4-dihydronicotinamide (NBzNH) has been studied anaerobically. Using conditions of excess substrate and following the decrease in absorbance of Eox (at 427 nm) with time, we observed biphasic kinetic behavior. The experimental data could be fitted to a scheme using two consecutive first-order processes, and rate constants could be determined for the two phases. A reasonable interpretation of our results is that a labile intermediate is formed in the reaction, as illustrated in Equation 4, where ES represents the intermediate. In this interpretation, the second, substrate-independent, slower phase of the reaction corresponds to the breakdown of the intermediate ES (fc3 step in Equation 4). The initial, faster phase of the reaction corresponds to the formation of the intermediate from Eox and N-benzyl-l,4-dihydronicotinamide. Using Equation 5, the calculated rate constants for this phase, fcf, can be related to Ks and k2- Values of kCat and Km were calculated from the relationships of Equations 6 and 7, using the measured values of the kinetic parameters k2, 3, and Ks, and the numbers obtained were in reasonable agreement with the values obtained aerobically. 

The rates of the oxidative steps in the citric acid cycle are limited by the rate of reoxidation of NADH and reduced ubiquinone in the electron transport chain which may sometimes be restricted by the availability of O2. However, in aerobic organisms this rate is usually determined by the concentration of ADP and/or P available for conversion to ATP in the oxidative phosphorylation process (Chapter 18). If catabolism supplies an excess of ATP over that needed to meet the cell s energy needs, the concentration of ADP falls to a low level, cutting off phosphorylation. At the same time, ATP is present in high concentration and acts as a feedback inhibitor for the catabolism of carbohydrates and fats. This inhibition is exerted at many points, a few of which are indicated in Fig. 

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