Insights from protein film voltammetry into mechanisms of complex biological electron-transfer reactions

Abstract

As the fundamental principles of long-range electron transfer (ET) in proteins are becoming well understood, interest is focusing on the mechanisms by which ET is coupled to chemical reactions such as ion transport and catalysis. Protein film voltammetry provides a powerful way to investigate these problems. The protein is immobilised on an electrode as an adsorbed electroactive film, typically a monolayer or less: then, by applying a potential, electrons are driven in and out of the active sites, resulting in diagnostically useful current signals. It is possible to resolve complex reactions over a wide dynamic range. For example, with cyclic voltammetry, scan rates exceeding 1000 V s⁻¹ can be used to observe coupling reactions that occur in the sub-millisecond time domain. For enzymes, catalysis can be measured as a function of potential to reveal processes that are mechanistically informative and may be involved in controlling activity. This paper will illustrate the capabilities of this approach for mechanistic investigations into biological redox chemistry.