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General Comment |
Suzuki T, et al have isolated three novel organic anion transporter cDNAs designated rat GST-1 (Gonad specific Transporter), rat GST-2, and human GST, expressed at high levels in the testis. Rat GST-1, GST-2, and Human GST consist of 748, 702, and 719 amino acids, respectively and all molecules possess the 12 predicted transmembrane domains, which is a common structure of organic anion transporters. Northern blot analyses and in situ hybridization revealed that both of the two rat molecules are highly expressed in the testis, especially in Sertoli cells, spermatogonia and Leydig cells. Weak signals are also detected in the epididymis and ovary in adult rat. The exclusive expression of human GST mRNA in the testis was confirmed by reverse transcription-polymerase chain reaction. The pharmacological experiments of Xenopus laevis oocytes injected with the respective rat GST-1- and GST-2-cRNAs revealed that both rat GST-1 and GST-2 transport taurocholic acid, dehydroepiandrosterone sulfate, and T4 with Michaelis Menten kinetics (taurocholic acid, Km = 8.9 and 2.5 micro M, dehydroepiandrosterone sulfate, Km = 25.5 and 21. micro M, and T4, Km = 6.4 and 5.8 for rat GST-1 and GST-2, respectively). 3,5,3'-triiodo-L-thyronine was also transported by rat GST-1 and GST-2. These data suggest that rat GST-1 and GST-2 might be one of the molecular entities responsible for transporting dehydroepiandrosterone sulfate and thyroid hormones involving in the regulating sex steroid transportation and spermatogenesis in the gonad.
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