The mechanism of osmotic adaptation in marine invertebraes. -Structural and functional characterization of taurine transporter

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The aim of this study is to elucidate the high ability of osmo-adaptation of marine invertebrates by investigation into the function of taurine transporter of marine invertebrates.In the first year (1999), we investigated into the change in free amino acid in the oyster exposed to the change in the ambient osmolality, and indicated that taurine was most important as an osmdyte in the oyster. Therefore, we made an attempt to clone the gene coding taurine transporter from marine invertebrates. As a result, we cloned a partial cDNA fragment showing high homology with taurine transporter of mammals from the marine mussel, while we could not clone that from the oyster.In the second year (2000), we obtained the full length of cDNA of mussel transporter showing high homology with taurine and betaine/GABA transporter. In addition, as a result of northern blot analysis, it is indicated that de novo transcription of this gene is induced by both hypo- and hyper-osmolality.In the last year (2001), we made an attempt to make the substrate of cloned transporter clear. In order to analyze the substrate spedficity of cloned transporter, we examined uptake activity of [^3H]amino acids, taurine and [^<14>C]betaine in the transporter expressed in the Xenopus oocyte. As a result, cloned transporter expressed oocyte showed the uptake activity to taurine and it is indicated cloned cDNA codes taurine transporter. In this study, taurine transporter was cloned from marine invertebrate for the first time, and it's partidpate in osmo-adaptation wasindicated. Our result is the first step toward the elucidation of the high ability in osmo-adaptation of marine invertebrates.