Dehydrogenase-Modified Electrodes Functioning as Biocatalyst Electrodes

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Modified electrodes carrying immobilized dehydrogenases could oxidize or reduce the substrate of the enzymes electrocatealytically by exchanging electrons between the prosthetic group of the immobilized enzyme and the electrode surface. This ytpe of electrodes, biocatalyst electrodes, could be used in such novel applications as biosensors, bioreactors, and biofuel cells. We immobilized D-gluconate dehydrogenase, GADH,(EC 1.1.99.3) form Pseudomanas fluorescens on the surface of a ubiquinone-mixed carbon paste electrode by irreversible adsorption. The GADH modified electrodes could oxidize-D-gluconate electrocatalytically, with ubiquinone serving as an electron transfer mediator between the carbon paste electrode and the immobilized enzyme. The effect of various factors on the current response of the electrode to D-gluconate was investigated, and the results were explained by the theory of biocatalyst electrode with an entrapped mediator which an entrapped mediator which was derived by the author. The practical use of the dehydrogenase modifeid as an amperometric sensor was examined. p-Benzoquinone, BQ, could be used as a mediator in place of ubiquinone and the presence of a semipermeable membrance coating the enzyme layer on the electrode surface was effective. It has been shown that the film-coated GADH carbon paste electrode with mixed-in BQ can be used as a D-gluconate sensor. A novel method measuring the substrate at high sensitivity was proposed, which uses a linear sweep voltammetry after a given period of waiting time in a test solution. Other dehydrogenases such as oligosaccharide dehydrogenase and glycerol dehydrogenase were also immobilized on the surface of carbon paste electrode with mixed-in BQ. The dehydrogenase modified electrodes showed currnet response to their substrates, and could be used as the sonsors for the substrates.