Biochemical and biophysical studies of photosystem I in Chlamydomonas reinhardtii: Directionality of electron transfer and state transitions

All life on earth is dependent upon the ability of plants, algae and cyanobacteria to convert sunlight into stored chemical energy. This process is very efficient, much more efficient than any man-made device. As our global energy crisis is being realized researchers look may look (bacterio-)chlorophyll containing organisms for clues to its solution. This dissertation addresses two fundamental aspects of photosynthesis that were studied with the model organism Chlamydomonas reinhardtii cc 125. First, the characterization of the PSI-LHCI supercomplex with respect to state transitions is described using spectroscopy and protein gel electrophoresis following sucrose density gradient centrifugation. Prior to centrifugation thylakoid membranes were solubilized with n-dodecyl-beta-D-maltoside. During these experiments a specific fraction was determined to be most suitable for the second part of this study, that investigates the directionality of electron transfer through photosystem I. Methionine-histidine mutants of the A0 acceptor ligand were generated to probe the electron transfer pathway using electron paramagnetic resonance. Results support the notion that electron transfer is bidirectional. The room temperature data suggest that a bias may exist towards electron transfer the A-side cofactors however at cryogenic temperatures there is evidence to supports a bias towards the B-side cofactors with respect to the ability to reduce the terminal iron-sulfur clusters, FA and FB.