Photoelectrochemical Monitoring of Photosystem I Electron Transport with Oxygen as Acceptor

Abstract

In the past few years, we have used a photoelectrochemical cell first described by Allen and Crane (1) and then modified by us (2) to study the photocurrent produced by thylakoid membranes. With this type of cell, the suspension of chloroplast membranes is introduced into a small compartment (80 µl) where the reduced species produced by the photosynthetic electron transport are used to generate a photocurrent at a platinum working electrode kept under potentiostatic conditions (750 mV vs SCE). It was demonstrated that photocurrent generated by either native thylakoid membranes or isolated PSI or PSII submembrane fractions could be greatly enhanced by the addition of artificial acceptors like potassium ferricyanide, methylviologen, or 2,5-dichlorobenzoquinone (2–4). The artificial electron acceptors acted as an electroactive mediator which carry the reduced equivalents from the membranes to the platinum electrode. However, we have also reported the generation of photocurrents in the absence of any added artificial electron acceptor (2,5). It was postulated that the photocurrent could be either generated by thylakoid membranes in close contact with the platinum electrode or mediated by impurities already present in the reaction medium (4,5)