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Title: An electrochemical study on mushroom o-diphenol:oxygen oxidoreductase
Author: Richardson, Pamela Joy
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1967
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A new electrochemical method employing purely passive circuitry has been developed to follow the course of certain enzymatic oxidations through the detection of electroactive molecular species produced in such reactions. The measuring system has been designed such that the electrical power consumed can be minimized, or, alternatively, the effects of power withdrawal illustrated. The method has been applied principally to a kinetic study of the system oxygen/catechol/o-diphenol:oxygen oxidoreductase. Investigations reveal the operation of two reaction regimes at pH 6.0, above and below 294°K, that with the higher temperature coefficient possessing the higher activation energy. Potassium chloride, which was noted to inhibit the reaction competitively at acid pH, was observed to act by curtailing the initial exceedingly fast phase of a polyphasic reaction, and drastically reducing the velocity of the succeeding reaction. It is postulated that chloride ions, established as the active species, compete with hydroxyl ions necessary to some stage of the reaction sequence. The pH optimum of the reaction has been noted to move from pH I.8 in the virtual absence of potassium chloride to pH 7.3 in the presence of 1.4 M. It is proposed that chloride ions increase the pKa, through influencing the ionization of group(s) at or adjacent to the active centre of the enzyme. Studies on a range of inhibitors,in the presence and absence of potassium chloride, illustrate the mechanism by which enzyme reactivation is effected through the intervention of a reactive reaction intermediate postulated to be o-benzoquinone. In agreement with the findings of workers employing alternative techniques, the induction period of enzymatic monophenol oxidation has been found to be dependent on both enzyme and substrate concentration. The method has been found adequately suited to the detection of the reaction kinetics of a catalase-free preparation of Beta-D-glucose: oxygen oxidoreductase on glucose.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available