Couple, oxidation-reduction

Transfer of hydrogen from one substrate to another in a coupled oxidation-reduction reaction (Figure 11-3). These dehydrogenases are specific for their substrates but often utilize common coenzymes or hydrogen carriers, eg, NAD". Since the reactions are re-... 

Finnegan, W. G., and R. L. Pitter, Preliminary Study of Coupled Oxidation-Reduction Reactions of Included Ions in Growing Ice Crystals—Reply, Atmos. Environ., 25, 2912-2913 (1991). 

Like RT3D, BioRedox is a 3-D model that is capable of modeling multi-species reactive transport [70]. The public domain model can simulate coupled oxidation-reduction reactions between multiple electron acceptors and donors. Except for rate-limited sorption, it is capable of simulating all the reactions simulated by RT3D, and is more user-friendly, in that no modifications to source code are required to incorporate reaction packages [70]. 

The basis of all electrochemical analysis is the transfer of electrons from one atom or molecule to another atom or molecule in an obligately coupled oxidation-reduction reaction (a redox reaction). 

In yeast and mycelial fungi, xylose is metabolized via coupled oxidation-reduction reactions . Xylose reductase is the enzyme involved in the reduction of xylose to xylitol. Sequential enzymatic events, through the oxidation of xylitol to xylulose, lead to the utilization of xylose. Many yeast species utilize xylose readily, but the ethanol production capability is very limited. Only a few yeast species effectively produce ethanol from xylose these include Pachysolen tan-nophilus, Candida shihatae and Pichia stipitis [80]. The production of ethanol from xylose by these three yeast strains has been studied extensively in recent years. Recently, genetically engineered yeast strains have been constructed for more effective conversion of xylose to ethanol. 

Unlike the oxidation of glucose by oxygen (as in a fire), most biological oxidations do not involve direct transfer of electrons from a substrate directly to oxygen. Instead, a series of coupled oxidation-reduction reactions occurs, with the electrons passed to intermediate electron carriers such as NAD+ before they are finally transferred to oxygen. 

Mechanisms for coprecipitation of lead and cobalt with manganese oxide can be derived based on thermodynamic calculations. They can explain the increased oxidation state of manganese reached in the mixed oxide precipitates, and they provide a potential control of the solubility of the accessory metals. The effectiveness of the control has been evaluated in a preliminary way by laboratory experiments described here, and by some fleld observations. Cobalt activity seems to be controlled by manganese coprecipitation in many natural systems. Although more testing by both laboratory experiments and fleld studies is needed, the proposed mechanisms appear to be applicable to many coupled oxidation-reduction processes. 

The discovery by Dr. Racker of enzjunes which catalyze the coupled oxidation-reduction. 

Marchand, P., Rosenfeld, E., Erable, B., Maugard, T., Lamare, S., and Goubet, I. (2008) Coupled oxidation-reduction of butanol-hexanal by resting Rhodococcus erythropolis NCIMB 13064 cells in liquid and gas phase. Enzyme Microb. Technol,... 

The electron-transport system is a series of coupled oxidation-reduction (also called redox) reactions which transfer electrons to molecular oxygen. Carrier 1 (Figure 13.2) in its oxidized form may accept electrons which reduce it. In the reduced state, it may donate the electrons to the oxidized form of carrier 2. In the process of the transfer, carrier 1 becomes reoxidized as carrier 2 becomes reduced. Similarly, reduced carrier 2 may donate electrons to carrier 3 and so on. In each reaction, the electron donor can only release the electrons if there is a suitable acceptor. The electron donor is termed the reductant since it reduces the acceptor and the electron acceptor is termed the oxidant since it oxidizes the donor. In the electron-transport system, each electron carrier oscillates between oxidized and reduced forms which constitute a redox couple. 

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