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Title: Electron transport reactions of denitrification
Author: Bell, Louise Carol
ISNI:       0000 0001 3455 7489
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1990
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A study is reported which demonstrates that electron transport to the reductase reactions of denitrification in the bacterium Thiosphaera pantotropha can occur aerobically. Use of dark-type electrodes has demonstrated that the N2O reductase enzyme of this organism is active under aerobic conditions, and that O2 and N2O reduction can occur simultaneously. The reduction of NO3- to N2 gas, even under aerobic conditions, is shown to proceed via NO as an intermediate. It is concluded that the reaction of NO with O2 must be sufficiently slow that it does not effectively compete with the reduction of NO to N2O. The ability of T. pantotropha to catalyse aerobic NO3- reduction, the first step of the aerobic denitrification process, is shown to correlate with the expression of a NO3- reductase enzyme that is located in the periplasm. This periplasmic enzyme is expressed, and is active, under both aerobic and anaerobic conditions. A membrane bound NO3- reductase is also expressed, but only under anaerobic conditions, by this organism. This latter reductase resembles the NO3- reductase of Paracoccus denitrificans in respect of both its catalytic properties and the inhibition of activity in intact cells under aerobic conditions. Mutants of T. pantotropha that lack the membrane bound NO3- reductase, and not only retain but overproduce the periplasmic enzyme, have been obtained via Tn5 mutagenesis. The periplasmic NO3- reductase identified in T. pantotropha bears catalytic and structural similarities to an enzyme previously characterised in some strains of Rhodobacter capsulatus. The ability of strains of R. capsulatus to reduce NO to N2O is reported together with evidence that there is a discrete NO reductase in this organism. The electron transport pathway to NO reductase has been elucidated. The first identification of a denitrifying strain of R. capsulatus is reported.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry