Voltammetry and Single‐Molecule In Situ Scanning Tunnelling Microscopy of the Redox Metalloenzyme Human Sulfite Oxidase. Issue 1 (4th January 2021)

• Record Type: Journal Article
• Authors: Yan, Jiawei; Frøkjær, Emil Egede; Engelbrekt, Christian; Leimkühler, Silke; Ulstrup, Jens; Wollenberger, Ulla; Xiao, Xinxin; Zhang, Jingdong
• Is Part Of: ChemElectroChem. Volume 8:Issue 1(2021)
• Page Start: 164
• Page End: 171
• Publication Date: 2021-01-04
• Subjects: cyclic voltammetry -- human sulfite oxidase -- in situ scanning tunnelling spectroscopy -- self-assembled molecular monolayers -- single-crystal gold electrodes; Electrochemistry -- Periodicals; 541.37
• DOI: 10.1002/celc.202001258
• Languages: English
• ISSNs: 2196-0216

Abstract

Abstract: Human sulfite oxidase ( h SO) is a homodimeric two‐domain enzyme central in the biological sulfur cycle. A pyranopterin molybdenum cofactor (Moco) is the catalytic site and a heme b 5 group located in the N‐terminal domain. The two domains are connected by a flexible linker region. Electrons produced at the Moco in sulfite oxidation, are relayed via heme b 5 to electron acceptors or an electrode surface. Inter‐domain conformational changes between an open and a closed enzyme conformation, allowing "gated" electron transfer has been suggested. We first recorded cyclic voltammetry (CV) of h SO on single‐crystal Au(111)‐electrode surfaces modified by self‐assembled monolayers (SAMs) both of a short rigid thiol, cysteamine and of a longer structurally flexible thiol, ω‐amino‐octanethiol (AOT). h SO on cysteamine SAMs displays a well‐defined pair of voltammetric peaks around −0.207 V vs. SCE in the absence of sulfite substrate, but no electrocatalysis. h SO on AOT SAMs displays well‐defined electrocatalysis, but only "fair" quality voltammetry in the absence of sulfite. We recorded next in situ scanning tunnelling spectroscopy (STS) of h SO on AOT modified Au(111)‐electrodes, disclosing, a 2–5 % surface coverage of strong molecular scale contrasts, assigned to single h SO molecules, notably with no contrast difference in the absence and presence of sulfite. In situ STS corroborated this observation with a sigmoidal tunnelling current/overpotential correlation. Abstract : Tunnel vision : Human sulfite oxidase ( h SO) is a homodimeric two‐domain enzyme, with a Mo catalytic cofactor and an electron‐transfer heme b 5, switching between open and closed conformations. Cyclic voltammetry on Au(111)‐electrodes modified by ω‐amino‐octanethiol monolayers gives well‐defined h SO electrocatalysis. Constant current in situ scanning tunnelling spectroscopy displays sigmoidal tunnelling current/overpotential correlations and a 2–5 % coverage of molecular scale contrasts, assigned to individual functional h SO molecules.