Structure and function of the photosynthetic membrane
Photosynthesis occurs in the chloroplasts where the photosynthetic membranes, the so-called thylakoids are located. They are responsible for the light reaction whereby light is captured and its energy converted to chemical energy in the form of ATP and NADPH concomitant with the development of oxygen. The thylakoids are made up of over a hundred membrane proteins which together with pigments, chlorophyll and carotenoids, and membrane lipids, mainly galactolipids, form a highly complex membrane system which not only carry out electron transport and ATP synthesis but also harvest light, with the help of the pigments in a very efficient way. In addition the thylakoids have a very ingenious system of repair and antioxidants for protection against damage caused by light and oxidative stress. Thylakoids are probably the most complicated of biological membranes. They are the most abundant of all biological membranes on earth.
My strategy for studying the structure and function of the thylakoids is, and has been, the classical chemical one i.e. fragmentation and separation. Isolated thylakoids are fragmented mechanically by sonication whereby sub-thylakoid membrane vesicles are formed. These vary in sizes and surface properties and are separated by a combination of centrifugation and aqueous two-phase partitioning. By using counter current distribution we have been able to separate the vesicles into 10 different distinct populations originating from different regions of the intact thylakoid membrane system. By using a “nearest neighbour” analysis (Albertsson et al. Biochim. Biophys. Acta 1098: 90-94,1991 and Q.Rev. Biophysics 21:61-98, 1988) it has been possible to analyse the domain structure of the thylakoid membrane and this has lead to a model for the structure and function of the thylakoid membrane (Trends on Plant Science 6:349-354, 2001 and Photosynthesis Research 46: 141-149, 1995).