The subcellular localization of the long-acting thyroid stimulator inhibitor in bovine thyroid gland.
To characterize further the nature and site of the receptor for the IgG stimulator in Graves' disease, we have developed a preparative scheme to provide a bovine thyroid subfraction rich in plasma membranes. Pellets (800 X g) obtained from bovine thyroid homogenates were layered on a 30-64% continuous sucrose gradient (SG). The centrifuged gradient was divided into four portions (SG1, 2, 3, and 4); and these along with the 800 X g pellet were characterized in terms of their capacity to neutralize (bind) the biological activity of LATS, their specific binding of [125I]TSH, and their subcellular marker content. Subfraction SG1 contained the highest adenyl cyclase specific activity, the highest [125I]TSH binding specific activity, and vied with the 800 X g pellet and SG3 for the highest specific activity of LATS neutralization. Electron microscopy of SG1 showed a predominance of plasma membrane structures contaminated with a modest amount of cellular debris. Adenyl cyclase activity in SG1 was enhanced by TSH, LATS, and sodium fluoride. Although a dose-response curve could be established for TSH, a similar relationship could not be established for LATS. We conclude that activation of plasma membrane-bound adenyl cyclase is associated with neutralization of the biological activity of LATS. Further, the difference between [125I]TSH binding and LATS neutralization activity observed in the various thyroid membrane subfractions suggests that either LATS and TSH interact at different sites or have different mechanisms of binding at a common site.
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001681:Biological Assay; D002417:Cattle; D002462:Cell Membrane / Q000032:analysis / Q000648:ultrastructure; D004789:Enzyme Activation; D008135:Long-Acting Thyroid Stimulator / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D008854:Microscopy, Electron; D009930:Organic Chemicals; D013347:Subcellular Fractions / Q000032:analysis / Q000648:ultrastructure; D013961:Thyroid Gland / Q000032:analysis* / Q000378:metabolism; D013972:Thyrotropin / Q000378:metabolism
D009930:Organic Chemicals; C018995:long-acting thyroid stimulator inhibitor; D013972:Thyrotropin; D008135:Long-Acting Thyroid Stimulator; D000262:Adenylyl Cyclases