packed with productive sites; (B) diffusion to an electrode having such a low population of productive sites that they behave as micro-electrodes; (C) a homogeneous adsorbed layer of noninteracting protein molecules.

The oxidation states of the entire population of centers under investigation are directly and immediately controlled by the applied potential. This achieves a much greater degree of control over redox-state dependent reactivities compared to conventional experiments that address freely diffusing molecules. It is also possible to apply potential pulses of precise value and duration to the sample: this exposes the active sites to oxidative or reductive stress, either of which can induce further reactions that may continue well after the pulse [36]. As will be described in Section IIIE, cyclic voltammetry experiments utilizing short, high-potential pulses have been used to study oxidative damage to [4Fe4S] clusters.