title: Electrostatic interaction between an enzyme and electrodes in the electric double layer examined in a view of direct electron transfer-type bioelectrocatalysis.
abstract: Effects of the electrode poential on the activity of an adsorbed enzyme has been examined by using copper efflux oxidase (CueO) as a model enzyme and by monitoring direct electron transfer (DET)-type bioelectrocatalysis of oxygen reduction. CueO adsorbed on bare Au electrodes at around the point of zero charge (E(pzc)) shows the highest DET activity, and the activity decreases as the adsorption potential (E(ad); at which the enzyme adsorbs) is far from E(pzc). We propose a model to explain the phenomena in which the electrostatic interaction between the enzyme and electrodes in the electric double layer affects the orientation and the stability of the adsorbed enzyme. The self-assembled monolayer of butanethiol on Au electrodes decreases the electric field in the outside of the inner Helmholtz plane and drastically diminishes the E(ad) dependence of the DET activity of CueO. When CueO is adsorbed on bare Au electrodes under open circuit potential and then is held at hold potentials (E(ho)) more positive than E(pzc), the DET activity of the CueO rapidly decreases with the hold time. The strong electric field with positive surface charge density on the metallic electrode (σ(M)) leads to fatal denaturation of the adsorbed CueO. Such denaturation effect is not so serious at E(ho)<<E(pzc), but the electric field with negative σ(M) induces an orientation inconvenient for the DET reaction during the adsorption process. A positively charged neomycin shows a promoter ability to CueO adsorbed at E(ad)<<E(pzc). The phenomenon is also explained on the proposed model.
authors: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors: Yu
authors: Y
authors: Sugimoto
authors: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan; Japan Science and Technology Agency, CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
authors: Yuki
authors: Y
authors: Kitazumi
authors: Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan.
authors: Seiya
authors: S
authors: Tsujimura
authors: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors: Osamu
authors: O
authors: Shirai
authors: Japan Science and Technology Agency, CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan; Department of Chemistry, Konan University, 8-9-1 Okamoto, Higashi-Nada, Kobe, Hyogo 658-8501, Japan.
authors: Masahiro
authors: M
authors: Yamamoto
authors: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan; Japan Science and Technology Agency, CREST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan. Electronic address: kano.kenji.5z@kyoto-u.ac.jp.
authors: Kenji
authors: K
authors: Kano
mesh_terms: D000327:Adsorption; D015374:Biosensing Techniques; D002384:Catalysis; D004560:Electricity; D004579:Electron Transport; D006046:Gold / Q000737:chemistry; D010088:Oxidoreductases / Q000737:chemistry / Q000302:isolation & purification*; D011489:Protein Denaturation; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013499:Surface Properties
chemical_list: D013438:Sulfhydryl Compounds; D006046:Gold; C025540:n-butyl mercaptan; D010088:Oxidoreductases; C024748:copper oxidase
keywords: Denaturation; Direct electron transfer; Electric double layer; Electric field; Orientation