Glucose reduction potential

In the case of two flavoenzyme oxidase systems (glucose oxidase (18) and thiamine oxidase s where both oxidation-reduction potential and semiquinone quantitation values are available, semiquinone formation is viewed to be kinetically rather than thermodynamically stabilized. The respective one-electron redox couples (PFl/PFl- and PFI7PFIH2) are similar in value (from essential equality to a 50 mV differential) which would predict only very low levels of semiquinone (32% when both couples are identical) at equilibrium. However, near quantitative yields (90%) of semiquinone are observed either by photochemical reduction or by titration with dithionite which demonstrates a kinetic barrier for the reduction of the semiquinone to the hydroquinone form. The addition of a low potential one-electron oxidoreductant such as methyl viologen generally acts to circumvent this kinetic barrier and facilitate the rapid reduction of the semiquinone to the hydroquinone form. 

Ethanol Production in Yeast When grown anaerobically on glucose, yeast (S. cerevisiae) converts pyruvate to acetaldehyde, then reduces acetaldehyde to ethanol using electrons from NADH. Write the equation for the second reaction, and calculate its equilibrium constant at 25 °C, given the standard reduction potentials in Table 13-7. 

Assuming that the sequence and reduction potentials shown in Figure 3-6 are correct, calculate (a) the ratio of NADPH/ATP/O produced in one noncyclic process and (b) the ATP yield of one cyclic process, (c) Calculate the efficiency of red light (A = 700 nm) in the overall synthesis of 1 mole of glucose from 6C02 + 6Hj0. Assume that each noncyclic process (4e ) yields 1 ATP and 1 NADPH and that each cyclic process (2 ) yields 1 ATP. (d) What would the efficiency be if each noncyclic process yielded 2 ATP+ 1 NADPH ... 

Stankovich, M. T., Schopfer, L. M., Massey, V., Determination of Glucose Oxidase Oxidation-Reduction Potentials and the Oxygen Reactivity of Fully Reduced Semiquinoid Forms , J. Biol. Chem. 253 (1978) 4971-4979. 

Inhibition of Mn and Fe reduction by electron acceptors with higher reduction potentials Reduction of Mn and Fe oxides during oxidation of glucose is shown below ... 

SERRS spectroelectrochemistry of adsorbed GO and FAD have shown that their reduction potentials are identical. This suggests that the protein may be denatured on the surface. This possibility is supported by our inability to observe catalytic activity for the adsorbed enz3rme. Reduction of the enzyme by glucose was not observed under anaerobic conditions. 

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