The overall objective is to relate the detailed supramolecular structure of the membrane-associated photsynthetic apparatus to the following steps in energy conversion: A) Absorption of light by bacteriochlorophyll c, B) Transfer of excitation energy to bacteriochlorophyll a, C) Energy transfer to the reaction center, and D) Electron transfer in the reaction center.
The specific aims of this proposal are to characterize further Chlorobium aminolipid, to find out whether this lipid is associated with reaction-center complexes in the cytoplasmic membrane or with bacteriochlorophyll a-proteins on the cytoplasmic membrane, to isolate and characterize the reaction center, to determine the role of bacteriopheophytin c and the state of specialized bacteriochlorophyll a (P840), and to isolate a bacteriochlorophyll c-lipid-protein complex from the chlorosome. In pursuit of these aims the aminolipid will be hydrolyzed in alkali, and the products will be characterized by ultraviolet, infrared, proton-NMR, and mass spectroscopy. Association of the aminolipid with reaction-center complexes will be tested by delipidating the complexes and correlating photochemical activity with residual lipid content. Orientation of the aminolipid in membranes will be examined by polarization of fluorescence (340 nm). Preparation of the reaction-center complex containing 35 bacteriochlorophyll a molecules will be carried out under varying conditions in an attempt to preserve photochemical activity. Electron-nuclear-double resonance technique will be used to determine whether the specialized bacteriochlorophyll a (P840) is a dimer. The isolation of a bacteriochlorophyll c-lipid-protein complex will be attempted by treating purified chlorosomes with gentle detergents. The proposed research is relevant to the general question of protein-lipid interactions in any biological membrane, including those of human cells.
