The proposed research is directed towards elucidation of the role of membranes in the visual process. In the broadest of terms, our goal is to determine the molecular events responsible for membrane excitability in the vertebrate rod. At this membrane level, several puzzling and outstanding questions are evident, which may be relevant to a better understanding of vision and its disorders. The most immediate objectives of the project can be grouped into three general areas: (i) investigation of the structural and dynamic properties of the highly polyunsaturated phsopholipids which comprise the fundamental bilayer matrix of the retinal disk membranes, (ii) studies of the conformation of rhodopsin and the nature of its interaction with the native retinal disk membrane phospholipids, as well as synthetic phospholipids used for membrane reconstitution and detergents used for membrane solubilization, (iii) studies of the role of electrical and osmotic forces in determining the properties of the lipid and protein components of the rod outer segment disk membranes. The above problems will be approached primarily through the use of various biophysical techniques. A major emphasis will be to further develop and employ nuclear magnetic resonance (NMR) methods for the study of both the protein and lipid components of the photoreceptor membrane. Such NMR methods are highly novel and are capable of providing detailed information regarding the ordering and motional properties of membrane constituents, without the introduction of probe molecules, which may perturb the bilayer structure. Thus, we intend to investigate problems such as the role of membrane thickness, degree of polyunsaturation, osmotic forces, transmembrane electrical potential in determining the conformation and proper photochemical functionality of rhodopsin. Using these methods, we hope to provide during the next five years a fairly complete picture of the mutual interaction of lipid and protein and their relation to function in the vertebrate rod outer segment, a particularly promising model fo excitable membranes in general.
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