It has been demonstrated by biochemical and autoradiographic techniques that taurine (2-aminoethanesulfonic acid) is the most abundant free amino acid in the retina attaining concentrations as high as 50-80 mM in the photoreceptor layer. Depletion of the taurine content of the rat retina induces abnormal visual function as measured by a decrease in the amplitude of the b wave of the electroretinogram. In addition, morphologic changes have also been reported to occur in the photoreceptor layer of the taurine-depleted rat. However, specific biochemical alterations have not been determined in this rat model. Thus, this proposal will address the hypotheses that molecular changes occur in retinal taurine binding proteins and taurine-stimulated calcium uptake proteins in the taurine depleted rat. Preliminary data from our laboratory indicate that taurine depletion produced by treating rats for one month with guanidinoethanesulfonic acid, a taurine transport inhibitor, produces alterations in both the taurine binding protein(s) and taurine-stimulated calcium uptake system(s). Therefore, we propose to solubilize, purify, and characterize both the taurine binding protein (s) and the taurine-stimulated calcium uptake protein(s) in th normal and taurine-depleted rat. Characterization of the taurine binding protein(s) will include the following: ion requirements, kinetic parameters, effects of taurine analogues, effects of hydrolytic enzymes, determination of Stokes radii and approximate molecular weights, and preparation of proteoliposome vesicles. In addition the taurine-stimulated calcium uptake protein(s) will also be characterized by determining the effects of ATP analogues and by determining whether the uptake proteins are phosphorylated. The significance of the proposed research will be to determine a molecular function for taurine in the retina. In addition information concerning the importance of the relationship between taurine deficiency and visual function will be acquired.
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