STUDIES ON THE MECHANISM OF VISUAL EXCITATION

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The long term goal of this research is to understand the process of visual excitation at the molecular level. We plan to explore all three stages of the visual excitation process: the intitial transduction event, where light absorbed by the visual pigment starts the excitation process; the mechanism by which the photo-activated rhodopsin initiates the biochemical events within the photoreceptor cell; and the control of photoreceptor plasma membrane permeability. We will study not only vertebrate rods, but also will develop methods using monocolonal antibodies to easily purify large quantities of cone and invertebrate photoreceptors and their associated visual pigments. While little is known biochemically or biophysically about either pigment, defects in the former are responsible for color blindness. We plan to study the structural changes in both the chromophore and the apoprotein when rhodopsin is transformed into its primary photoproduct and in particular look for evidence of light energy being transformed to chemical energy by charge separation. We will investigate both the nature and structural basis for probable binding of divalent cations by rhodopsin, and for the light initiated interaction of rhodopsin with enzymes involved in cGMP metabolism in the rods. There is growing evidence that certain aspects of retinitis pigmentosa may be due to defects in the light activated enzyme system. To investigate these interactions we will use a wide variety of techniques including protein and chromophore modification; and circular dichroic, low temperature, fluorescence, and vibrational spectroscopy. Finally we will study the control of ion channels in rod membranes by trying to isolate and purify both the plasma membrane and the ion channels using monoclonal antibodies.