NMR STUDIES OF CHLOROPHYLL A IN PHOTOSYNTHETIC MEMBRANE

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Photosynthesis is one of the basic processes in nature in which the energy of sunlight is efficiently converted into chemical energy, a reaction as yet difficult to mimic in vitro. While the function of chlorophylls in the photosynthetic process is reasonably well defined, the structural organization of the light-harvesting chlorophylls in the thylakoid is a subject of considerable current interest. The proposed research extends work carried out during the previous funding period on the organization of chlorophyll alpha in dimyristoyllecithin bilayer membranes. In this project, high field deuterium (2H) NMR spectroscopy will be used as the principal technique to study the specific interactions between chlorophyll and the thylakoid lipids. 2H-NMR relaxation measurements provide an ideal means of observing slow motions in lipid bilayers. 2H is a quadrupolar nucleus, and the quadrupolar interaction dominates other spin interactions in the 2H NMR relaxation expression. In addition, the lipid hydrocarbon chains may be deuterated at a single position allowing selective observation of a particular region of the bilayer. We will use the angular dependence of the spin-spin relaxation rate (T2-1) and the dependence of T2-1 on the order parameter to characterize the nature of slow motions and to determine the contribution of director fluctuations to T2-1 in the galactolipid membrane and in the presence of chlorophyll alpha. Ancillary techniques will include optical spectroscopy and chromatography as requisite for the isolation, purification and purity determination of chlorophylls and lipids, and will include differential scanning calorimetry as an adjunct to the NMR technique. This research project should shield useful information on the phase behavior, interaction and dynamics of chlorophyll alpha in lipid membranes. The project will also provide student participants with research exposure and training in biomedical research, thereby motivating students to pursue a career in biomedical research through close counseling and supervision, as well as through group dynamics of the research project team.