Sulphydryl modification inhibits taurine transport in human placental brush border membranes.
Taurine, 2-aminoethanesulphonic acid, is a -amino acid required for mammalian development. Although the human fetus accumulates taurine in many tissues, it has limited capacity for synthesis. The majority of fetal taurine is derived from the mother via placental transfer. The objective of this study was to analyse the functional groups involved in the taurine transport system of human placental brush-border membranes. Sulphydryl modifying reagents N-ethylmaleimide (NEM) and pyridyldithioethyl-amine (PDA) caused a dose-dependent inhibition of taurine uptake by brush-border membrane vesicles. Inhibition by PDA was reversible upon reduction by dithiothreitol but not by glutathione indicating that sulphydryl group(s) are located within the bilayer. Preincubation of brush-border membranes with taurine but not with taurocholate, before exposure to NEM, protected taurine transport function. Labelling studies using NEM and chemical cross-linking indicated that a 37.5 kDa protein was protected. These results demonstrate that sulphydryls located within the membrane bilayer are important for taurine transport in human placental brush-border membranes and suggest that a 37.5 kDa protein may be associated with Na(+)-dependent regulation of the taurine transporter.
Dumaswala
R
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Division of Pediatric Gastroenterology and Nutrition, Children's Hospital Research Foundation, Cincinnati, OH 45229, USA.
Brown
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TL
D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D003432:Cross-Linking Reagents; D004220:Disulfides / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D006801:Humans; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D008871:Microvilli / Q000187:drug effects* / Q000378:metabolism*; D010920:Placenta / Q000648:ultrastructure*; D011247:Pregnancy; D011725:Pyridines / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D013654:Taurine / Q000378:metabolism*; D000099247:Taurine Transporters
D002352:Carrier Proteins; D003432:Cross-Linking Reagents; D004220:Disulfides; D005033:Ethylmaleimide; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D011725:Pyridines; D012964:Sodium; D013439:Sulfhydryl Reagents; D013654:Taurine; D000099247:Taurine Transporters; C055639:pyridyldithioethylamine