PHOTOELECTROCHEMISTRY OF THYLAKOID AND SUB-THYLAKOID MEMBRANE PREPARATIONS - CYCLIC VOLTAMMETRY AND ACTION SPECTRA

A study involving a simple single compartment photoelectrochemical cell has been undertaken to assess its potential for studying the photoelectrogenic reactions in thylakoid and sub-thylakoid membrane preparations. The cyclic voltammetry technique has been used to follow the redox species formed in solution resulting from photoinduced electron transfer events of PS II and PS I enriched submembrane fractions and their specific artificial electron donors and acceptors. Compared to the photoresponse of whole thylakoid membranes, the behavior of the submembrane fractions in the presence of the electron acceptors 2,5-dichlorobenzoquinone and methylviologen (PS II and PS I specific acceptors, respectively) and of the PS I donor duroquinone, demonstrates the electrochemical reaction pathways and the limiting reactions of electron transport involved in photocurrent generation. The action spectra of the three membrane preparations in the photoelectrochemical cell were also recorded and indicate the pigments involved in photocurrent generation. These spectra show distinct preparation-dependent variations, both in the position and in the relative intensity of the peaks. Carotenoids have been shown to be large contributors to the photocurrent signal in thylakoid and PS II enriched membranes. Collectively, the data support the application of the photoelectrochemical cell to studying not only the acceptor side of PS I but also inter- and intra-photosystem electronic events.