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Redox properties and catalytic activity of surface-bound human sulfite oxidase studied by a combined surface enhanced resonance Raman spectroscopic and electrochemical approach
Citation key Sezer2010
Author Sezer, Murat and Spricigo, Roberto and Utesch, Tillmann and Millo, Diego and Leimkuehler, Silke and Mroginski, Maria A. and Wollenberger, Ulla and Hildebrandt, Peter and Weidinger, Inez M.
Pages 7894-7903
Year 2010
ISSN 1463-9076
DOI 10.1039/b927226g
Address THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND
Journal PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 12
Number 28
Publisher ROYAL SOC CHEMISTRY
Abstract Human sulfite oxidase (hSO) was immobilised on SAM-coated silver electrodes under preservation of the native heme pocket structure of the cytochrome b5 (Cyt b5) domain and the functionality of the enzyme. The redox properties and catalytic activity of the entire enzyme were studied by surface enhanced resonance Raman (SERR) spectroscopy and cyclic voltammetry (CV) and compared to the isolated heme domain when possible. It is shown that heterogeneous electron transfer and catalytic activity of hSO sensitively depend on the local environment of the enzyme. Increasing the ionic strength of the buffer solution leads to an increase of the heterogeneous electron transfer rate from 17 s(-1) to 440 s(-1) for hSO as determined by SERR spectroscopy. CV measurements demonstrate an increase of the apparent turnover rate for the immobilised hSO from 0.85 s(-1) in 100 mM buffer to 5.26 s(-1) in 750 mM buffer. We suggest that both effects originate from the increased mobility of the surface-bound enzyme with increasing ionic strength. In agreement with surface potential calculations we propose that at high ionic strength the enzyme is immobilised via the dimerisation domain to the SAM surface. The flexible loop region connecting the Moco and the Cyt b5 domain allows alternating contact with the Moco interaction site and the SAM surface, thereby promoting the sequential intramolecular and heterogeneous electron transfer from Moco via Cyt b5 to the electrode. At lower ionic strength, the contact time of the Cyt b5 domain with the SAM surface is longer, corresponding to a slower overall electron transfer process.
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