Bovine cytochrome c oxidase has been successfully immobilized in elect rode-supported lipid bilayer membranes to investigate the effect of cyanide binding on the oxidation of ferrocytochrome c and the electroreduction of dioxygen. Cyanide binding to oxidase was found to be reversible and exhibited 1: 1 stoichiometry. Binding constants (K) were also determined for binding of cyanide to the reduced (62 mu M) and oxidized (195 mu M) forms of the oxidase. The cytochrome c oxidase-modified electrodes described here could potentially be used as an amperometric biosensor for the detection of cyanide. (c) 2005 Elsevier B.V. All rights reserved.