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Originally published as Biophys J. BioFAST on August 25, 2006.
doi:10.1529/biophysj.106.089755
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Biophysical Journal 91:3897-3906 (2006)
© 2006 The Biophysical Society

Voltammetry and In Situ Scanning Tunneling Microscopy of Cytochrome c Nitrite Reductase on Au(111) Electrodes

James D. Gwyer *, Jingdong Zhang {dagger}, Julea N. Butt * {ddagger} and Jens Ulstrup {dagger}

* School of Chemical Sciences and Pharmacy, and {ddagger} School of Biological Sciences, Centre for Metalloprotein Spectroscopy and Biology, University of East Anglia, Norwich NR4 7TJ, United Kingdom; and {dagger} Department of Chemistry and NanoDTU, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark

Correspondence: Address reprint requests to Prof. Jens Ulstrup, Dept. of Chemistry and NanoDTU, Bldg. 207, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark. Tel.: 45-45252359; Fax: 45-45883136; E-mail: ju{at}kemi.dtu.dk; or Dr. Julea Butt, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK. Tel.: 44-1603 593877; Fax: 44-1603 592003; E-mail: j.butt{at}uea.ac.uk.

Escherichia coli cytochrome c nitrite reductase (NrfA) catalyzes 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 submonolayer coverage resolved by in situ STM is readily reconciled with the failure to detect nonturnover 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.




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J. H. van Wonderen, B. Burlat, D. J. Richardson, M. R. Cheesman, and J. N. Butt
The Nitric Oxide Reductase Activity of Cytochrome c Nitrite Reductase from Escherichia coli
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