title: Using scanning electrochemical microscopy (SECM) to measure the electron-transfer kinetics of cytochrome c immobilized on a COOH-terminated alkanethiol monolayer on a gold electrode.
abstract: Cytochrome c was electrostatically immobilized onto a COOH-terminated alkanethiol self-assembled monolayer (SAM) on a gold electrode at ionic strengths of less than 40 mM. Scanning electrochemical microscopy (SECM) was used to simultaneously measure the electron transfer (ET) kinetics of the bimolecular ET between a solution-based redox mediator and the immobilized protein and the tunneling ET between the protein and the underlying gold electrode. Approach curves were recorded with ferrocyanide as a mediator at different coverages of cytochrome c and at different substrate potentials, allowing the measurement of k(BI) = 2 x 10(8) mol(-1) cm3 s(-1) for the bimolecular ET and k degrees = 15 s(-1) for the tunneling ET. The kinetics of ET was also found to depend on the immobilization conditions of cytochrome c: covalent attachment gave slightly slower tunneling ET values, and a mixed CH3/COOH-terminated ML gave faster tunneling ET rates. This is consistent with previous studies and is believed to be related to the degree of mobility of cyt c in its binding configuration and its orientation with respect to the underlying electrode surface.
authors.affiliation: Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom. k.b.holt@ucl.ac.uk
authors.forename: Katherine B
authors.initials: KB
authors.lastname: Holt
mesh_terms: D000473:Alkanes / Q000737:chemistry; D000818:Animals; D045304:Cytochromes c / Q000378:metabolism*; D004563:Electrochemistry / Q000379:methods; D004579:Electron Transport; D004800:Enzymes, Immobilized / Q000378:metabolism; D006046:Gold; D066298:In Vitro Techniques; D007700:Kinetics; D008839:Microelectrodes; D008853:Microscopy / Q000379:methods; D008954:Models, Biological; D010084:Oxidation-Reduction; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D000473:Alkanes; D004800:Enzymes, Immobilized; D013438:Sulfhydryl Compounds; D006046:Gold; D045304:Cytochromes c