title: Effective Electrochemistry of Human Sulfite Oxidase Immobilized on Quantum-Dots-Modified Indium Tin Oxide Electrode.
abstract: The bioelectrocatalytic sulfite oxidation by human sulfite oxidase (hSO) on indium tin oxide (ITO) is reported, which is facilitated by functionalizing of the electrode surface with polyethylenimine (PEI)-entrapped CdS nanoparticles and enzyme. hSO was assembled onto the electrode with a high surface loading of electroactive enzyme. In the presence of sulfite but without additional mediators, a high bioelectrocatalytic current was generated. Reference experiments with only PEI showed direct electron transfer and catalytic activity of hSO, but these were less pronounced. The application of the polyelectrolyte-entrapped quantum dots (QDs) on ITO electrodes provides a compatible surface for enzyme binding with promotion of electron transfer. Variations of the buffer solution conditions, e.g., ionic strength, pH, viscosity, and the effect of oxygen, were studied in order to understand intramolecular and heterogeneous electron transfer from hSO to the electrode. The results are consistent with a model derived for the enzyme by using flash photolysis in solution and spectroelectrochemistry and molecular dynamic simulations of hSO on monolayer-modified gold electrodes. Moreover, for the first time a photoelectrochemical electrode involving immobilized hSO is demonstrated where photoexcitation of the CdS/hSO-modified electrode lead to an enhanced generation of bioelectrocatalytic currents upon sulfite addition. Oxidation starts already at the redox potential of the electron transfer domain of hSO and is greatly increased by application of a small overpotential to the CdS/hSO-modified ITO.
authors.affiliation: Institute of Biochemistry and Biology and ‡Institute of Chemistry, University of Potsdam , Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany.
authors.forename: Ting
authors.initials: T
authors.lastname: Zeng
authors.affiliation: Institute of Biochemistry and Biology and ‡Institute of Chemistry, University of Potsdam , Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Leimkühler
authors.affiliation: Institute of Biochemistry and Biology and ‡Institute of Chemistry, University of Potsdam , Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Koetz
authors.affiliation: Institute of Biochemistry and Biology and ‡Institute of Chemistry, University of Potsdam , Karl-Liebknecht-Strasse 24-25, 14476 Potsdam-Golm, Germany.
authors.forename: Ulla
authors.initials: U
authors.lastname: Wollenberger
mesh_terms: D002384:Catalysis; D004560:Electricity; D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D004800:Enzymes, Immobilized / Q000378:metabolism*; D006801:Humans; D008027:Light; D010084:Oxidation-Reduction; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D011094:Polyethyleneimine / Q000737:chemistry; D045663:Quantum Dots / Q000378:metabolism*; D013447:Sulfites / Q000378:metabolism; D017971:Tin Compounds / Q000494:pharmacology*
chemical_list: D004800:Enzymes, Immobilized; D013447:Sulfites; D017971:Tin Compounds; C109984:indium tin oxide; D011094:Polyethyleneimine; D050862:Oxidoreductases Acting on Sulfur Group Donors; C503599:SUOX protein, human; D010100:Oxygen
keywords: CdS quantum dots; bioelectrocatalysis; direct electrochemistry; human sulfite oxidase; photocurrent