Evidence demonstrates that taurine, present in high concentrations in the vertebrate retina, is an essential amino acid for the integrity of visual structures. Depletion of taurine in both animals and man has resulted in electrophysiologic and morphologic abnormalities. There is little information as how taruine is functioning at the molecular level. Thus, this proposal will address the following hypotheses: 1) that taurine produces changes in retinal proteins at the molecular level, and 2) that the effects of taurine on calcium ion uptake in the retina are related to the effects of taurine on protein phosphorylation. In previous studies from this laboratory it was reported that taurine inhibits the phosphorylation of specific retinal proteins. The animal tissue to be used in the experiments will be the rat retina. Two preparations of rat retina will be utilized: 1) a crude retinal homogenate, and 2) a P1 fraction which contains photoreceptor cell synaptosomes prepared by differential centrifugations in sucrose.
Specific aims will be to investigate the influence of taurine and taurine analogues on calcium ion uptake and protein phosphorylation at both low (10 MuM) and high (2.5 mM) calcium ion concentrations. The retinal kinase that is inhibited by taurine will be purified and characterized by routine biochemical techniques. The relationship of calcium ion uptake and protein phosphorylation in the taurine-depleted retina will be studied. The animals will be made approximately 70% taurine deficient by treating with guanidinoethanesulfonic acid, a taurine transport inhibitor. Finally, it is proposed to determine the site of the specific protein in the retina whose phosphorylation is inhibited by taurine by isolating and purifying the protein, producing monoclonal antibodies to the protein, and then localizing the protein in the retina by immunohistochemical techniques. The significance of the research will be to determine a function for taurine in the retina at the molecular level. Previous results such as inhibition of protein phosphorylation and alteration of the transition temperatures in Arrhenius plots of calcium ion uptake indicate that taurine is indeed affecting biological processes at the molecular level.

National Institute of Health (NIH)
National Eye Institute (NEI)
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Visual Sciences A Study Section (VISA)
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Texas Tech University
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Lombardini, J B (1994) The inhibitory effects of taurine on protein phosphorylation: comparison of various characteristics of the taurine-affected phosphoproteins present in rat retina, brain and heart. Adv Exp Med Biol 359:9-17
Lombardini, J B (1993) Spontaneous and evoked release of [3H]taurine from a P2 subcellular fraction of the rat retina. Neurochem Res 18:193-202
Sufrin, J R; Lombardini, J B; Alks, V (1993) Differential kinetic properties of L-2-amino-4-methylthio-cis-but-3-enoic acid, a methionine analog inhibitor of S-adenosylmethionine synthetase. Biochim Biophys Acta 1202:87-91
Lombardini, J B (1993) Partial characterization of an approximately 20 K M(r) retinal protein whose phosphorylation is inhibited by taurine. Biochem Pharmacol 46:1445-51
Lombardini, J B (1992) Effects of taurine on the phosphorylation of specific proteins in subcellular fractions of the rat retina. Neurochem Res 17:821-4
Lombardini, J B (1992) Effects of taurine on protein phosphorylation in mammalian tissues. Adv Exp Med Biol 315:309-18
Lombardini, J B (1992) Potassium-stimulated release of taurine in a crude retinal preparation obtained from the rat is calcium independent. Adv Exp Med Biol 315:399-404
Lombardini, J B (1991) Taurine: retinal function. Brain Res Brain Res Rev 16:151-69
Li, Y P; Lombardini, J B (1991) Taurine inhibits protein kinase C-catalyzed phosphorylation of specific proteins in a rat cortical P2 fraction. J Neurochem 56:1747-53
Li, Y P; Lombardini, J B (1991) Inhibition by taurine of the phosphorylation of specific synaptosomal proteins in the rat cortex: effects of taurine on the stimulation of calcium uptake in mitochondria and inhibition of phosphoinositide turnover. Brain Res 553:89-96

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