Excitation trapping and charge separation in Photosystem II in the presence of an electrical field |
| |
Authors: | RF Meiburg HJ Van Gorkom RJ Van Dorssen |
| |
Institution: | Department of Biophysics, Huygens Laboratory of the State University, P.O. Box 9504, 2300 RA Leiden The Netherlands |
| |
Abstract: | To investigate the effects of a membrane potential on excitation trapping and charge separation in Photosystem II we have studied the chlorophyll fluorescence yield in osmotically swollen chloroplasts subjected to electrical field pulses. Significant effects were observed only in those membrane regions where a large membrane potential opposing the photochemical charge separation was built up. When the fluorescence yield was low, close to F0, a much higher yield, up to Fmax, was observed during the presence of the membrane potential. This is explained by an inhibition by the electrical field of electron transfer to the quinone acceptor Q, resulting in a decreased trapping of excitations. A field pulse applied when the fluorescence yield was high, Q and the donor side being in the reduced state, had the opposite effect: the fluorescence was quenched nearly to F0. This field-induced fluorescence quenching is ascribed to reversed electron transfer from Q? to the intermediate acceptor, pheophytin. Its field strength dependence suggests that the midpoint potential difference between pheophytin and Q is at most about 300 mV. Even then it must be assumed that electron transfer between pheophytin and Q spans 90% of the potential difference across the membrane. |
| |
Keywords: | Charge separation Photosystem II Excitation trapping Membrane potential Fluorescence yield (Spinach chloroplast) DCMU 3-(3′ 4′-dichlorophenyl)-1 l-dimethylurea PS photosystem P-680 pheophytin Q electron donor the intermediary electron acceptor and the first stable electron acceptor in the reaction center of PS II Tricine |
本文献已被 ScienceDirect 等数据库收录! |
|