Evaluations of reduction potential data in relation to coupling, kinetics and function

This commentary addresses the effect and measurement of time-dependent contributions to reduction potentials. Reduction potentials form the basis for many quantitative or semi-quantitative judgements in biological redox chemistry. However, since data are obtained under an assumption of equilibrium being established, their relevance to biological functions requires consideration of the kinetics of the subprocesses that contribute to or influence the overall free energy change. Initial and final states effective in rapid and complex biological functions may differ considerably from those analysed after slow equilibration in a sample tube. A shortcoming of traditional potentiometric measurements is that the time domain is not probed. Voltammetry, a technique that has been much less widely applied in biological chemistry than in chemistry, examines redox transformations in both potential and time domains, and may enable a more realistic picture to be derived.