title: Direct electrochemistry and intramolecular electron transfer of ascorbate oxidase confined on L-cysteine self-assembled gold electrode.
abstract: A direct electrochemistry and intramolecular electron transfer of multicopper oxidases are of a great importance for the fabrication of these enzyme-based bioelectrochemical-devices. Ascorbate oxidase from Acremonium sp. (ASOM) has been successfully immobilized via a chemisorptive interaction on the l-cysteine self-assembled monolayer modified gold electrode (cys-SAM/AuE). Thermodynamics and kinetics of adsorption of ASOM on the cys-SAM/AuE were studied using cyclic voltammetry. A well-defined redox wave centered at 166±3mV (vs. Ag│AgCl│KCl(sat.)) was observed in 5.0mM phosphate buffer solution (pH7.0) at the fabricated ASOM electrode, abbreviated as ASOM/cys-SAM/AuE, confirming a direct electrochemistry, i.e., a direct electron transfer (DET) between ASOM and cys-SAM/AuE. The direct electrochemistry of ASOM was further confirmed by taking into account the chemical oxidation of ascorbic acid (AA) by O2 via an intramolecular electron transfer in the ASOM as well as the electrocatalytic oxidation of AA at the ASOM/cys-SAM/AuE. Thermodynamics and kinetics of the adsorption of ASOM on the cys-SAM/AuE have been elaborated along with its direct electron transfer at the modified electrodes on the basis of its intramolecular electron transfer and electrocatalytic activity towards ascorbic acid oxidation and O2 reduction. ASOM saturated surface area was obtained as 2.41×10(-11)molcm(-2) with the apparent adsorption coefficient of 1.63×10(6)Lmol(-1). The ASOM confined on the cys-SAM/AuE possesses its essential enzymatic function.
authors.affiliation: Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259-G1-5 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan; Interfacial Nanostructure Research Lab., The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Bhushan
authors.initials: B
authors.lastname: Patil
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Shigenori
authors.initials: S
authors.lastname: Fujikawa
authors.forename: Takeyoshi
authors.initials: T
authors.lastname: Okajima
authors.forename: Lanqun
authors.initials: L
authors.lastname: Mao
authors.forename: Takeo
authors.initials: T
authors.lastname: Ohsaka
mesh_terms: D000164:Acremonium / Q000201:enzymology; D000327:Adsorption; D001204:Ascorbate Oxidase / Q000737:chemistry* / Q000378:metabolism; D055162:Biocatalysis; D003545:Cysteine / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D004579:Electron Transport; D004800:Enzymes, Immobilized / Q000737:chemistry* / Q000378:metabolism; D006046:Gold / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013816:Thermodynamics
chemical_list: D004800:Enzymes, Immobilized; D006046:Gold; D001204:Ascorbate Oxidase; D003545:Cysteine
keywords: AA; Anodic current; Apo form of ascorbate oxidase from Acremonium sp.; Apo-ASOM; Ascorbate oxidase; Ascorbic acid; AuE; C bulk AA; C surf AA; C(ASOM); Concentration of AA in the bulk solution; Concentration of ASOM; Cysteine; Direct electron transfer; Gold electrode; I(a); Intramolecular electron transfer; Local concentration of AA in the vicinity of the ASOM confined on the cys-SAM/AuE; SOD; Saturated surface coverage of ASOM on the electrode surface; Self-assembled monolayer; Semidehydroascorbate radical; Superoxide dismutase; Surface coverage of ASOM on the electrode surface; T1; T2; T3; Type 1 copper active site in the ASOM; Type 2 copper active site in the ASOM; Type 3 copper active site in the ASOM; Γ(ASOM); Γ(s)(ASOM)