Title

Ferredoxin-mediated electrocatalytic dehalogenation of haloalkanes by cytochrome P450(cam)

Document Type

Article

Publication Date

2-16-2000

Abstract

The potential role of cytochrome P450(cam) in bioremediation has been extensively studied because of its ability to carry out the nonphysiological reductive dehalogenation of haloalkanes. The reductive dehalogenation catalytic cycle requires the input of two reducing equivalents, typically delivered to the enzyme from NADH via putidaredoxin reductase and putidaredoxin. In this report we present evidence demonstrating that in the presence of polylysine, spinach ferredoxin acts as an efficient electron shuttle between an indium-doped tin oxide (ITO) electrode and substrate-bound cytochrome P450(cam). The ferredoxin-mediated electrochemical reduction of substrate-bound cytochrome P450(cam) conduces to the reductive dehalogenation of haloalkanes. Consequently, this strategy permits the replacement of NADH and cytochrome P450 reductase, both expensive and fragile species, with an electrode to catalyze dehalogenation reactions. To accomplish this goal it was necessary to implement a system in which the electrode exchanged electrons with spinach ferredoxin, even in the presence of an excess of cytochrome P450(cam), which possesses a reduction potential more positive than that of spinach ferredoxin. This molecular discrimination at the electrode surface was achieved by capitalizing on surface electrostatic potentials typically exhibited by electron-transfer proteins. In this particular case, the positive electrostatic potential imparted by polylysine to the electrode surface steers spinach ferredoxin toward the electrode with an orientation optimal for heterogeneous electron exchange, thus acting as a good promoter for its electrochemistry. In contrast, cytochrome P450(cam) does not exchange electrons with the ITO electrode but instead is readily reduced in solution by accepting an electron from spinach ferredoxin. Digital simulation of the voltammetric experiments aimed at demonstrating the reductive dehalogenation electrocatalytic activity produced important insights into the mechanism of reductive dehalogenations carded out by cytochrome P450(cam).

Publication Source (Journal or Book title)

Journal of the American Chemical Society

First Page

1047

Last Page

1056

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