SPECTROSCOPY, IMAGING, OTHER TECHNIQUES |
Voltammetry and in situ scanning tunnelling
microscopy of
cytochrome c nitrite reductase on Au(111)-electrodes
James D Gwyer 1, Jingdong Zhang 2, Julea N Butt 1* and Jens Ulstrup 2
1 University of East Anglia
2 Technical University of Denmark
* To whom correspondence should be addressed. E-mail: j.butt{at}uea.ac.uk.
Submitted on June 9, 2006
Revised on July 10, 2006
Accepted on 15 August 2006
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Abstract |
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Escherichia coli cytochrome c nitrite reductase (NrfA) catalyses the six-electron reduction of nitrite to perform an important role in the biogeochemical cycling of nitrogen. Here we describe NrfA adsorption on single-crystal Au(111) electrodes as an electrocatalytically active film in which the enzyme undergoes direct electron exchange with the electrode. The adsorbed NrfA has been imaged to molecular resolution by in situ scanning tunneling microscopy (in situ STM) under full electrochemical potential control and under conditions where the enzyme is electrocatalytically active. Details of the density and orientational distribution of NrfA molecules are disclosed. The sub-monolayer coverage resolved by in situ STM is readily reconciled with the failure to detect non-turnover signals in cyclic voltammetry of the NrfA films. The molecular structures show a range of lateral dimensions. These are suggestive of a distribution of orientations that could account for the otherwise anomalously low turnover number calculated for the total population of adsorbed NrfA molecules when compared with that determined for solutions of NrfA. Thus, comparison of the voltammetric signals and in situ STM images offers a direct approach to correlate electrocatalytic and molecular properties of the protein layer, a long-standing issue in protein film voltammetry.
Key Words:
catalysis, electrochemistry, enzyme, heme, in situ STM, protein film voltammetry
