Role of carbohydrates in thyrotropin binding sites.
The role of carbohydrates in thyrotropin binding was studied by glycosidase treatment of human thyroid membranes. Removal of over 75% of membrane sialic acid resulted in a 50% increase of TSH binding, measured in 10 mM Tris-HCl, 50 mM NaCl, 0.1% bSA, pH 7.4, 37 degrees C (buffer A). This augmentation was due to an increase in binding to high affinity sites (Ka 1 X 10(10)M-1). The binding was highly specific and was not significantly inhibited by gangliosides. In contrast, low affinity binding of TSH was unchanged either in buffer A or in 10 mM Tris-acetate, 0.1% bSA pH 6.0, 4 degrees C (buffer B) and was inhibited by gangliosides. Treatment of membranes with beta-galactosidase, beta-N-acetylglucosaminidase and alpha-L-fucosidase had little effect on TSH binding. The data suggests that membrane-associated sialic acid inhibits TSH binding to high affinity receptors and that gangliosides are not involved in tthis TSH-receptor interaction.
D001665:Binding Sites; D002241:Carbohydrates / Q000502:physiology*; D005732:Gangliosides / Q000494:pharmacology / Q000502:physiology; D006062:Gonadotropins / Q000378:metabolism; D006596:Hexosaminidases / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D009439:Neuraminidase / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000187:drug effects; D012794:Sialic Acids / Q000502:physiology; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000378:metabolism*; D005644:alpha-L-Fucosidase / Q000494:pharmacology; D001616:beta-Galactosidase / Q000494:pharmacology
D002241:Carbohydrates; D005732:Gangliosides; D006062:Gonadotropins; D011956:Receptors, Cell Surface; D012794:Sialic Acids; D013972:Thyrotropin; D006596:Hexosaminidases; D009439:Neuraminidase; D001616:beta-Galactosidase; D005644:alpha-L-Fucosidase