A water-soluble fragment of the thyroid-stimulating hormone receptor which binds both thyroid-stimulating hormone and thyroid-stimulating hormone receptor antibodies.
Previous studies have shown that freezing and thawing of human thyroid homogenates releases a water-soluble substance which reversibly binds to TSH-receptor antibodies. This substance has been designated long-acting thyroid stimulator absorbing activity (LAA). We now describe a new method for measuring LAA based on the TSH-receptor assay and application of the technique to the study of LAA. Our results indicate that LAA is a heat-labile glycoprotein which co-elutes with haemoglobin on gel filtration. Furthermore, LAA is retarded by columns of Sepharose-TSH but not by Sepharose coupled to human chorionic gonadotrophin, normal immunoglobulin G or bovine serum albumin, suggesting that LAA contains a binding site for TSH as well as for TSH-receptor antibodies. It would seem therefore that LAA is a water-soluble fragment of the TSH receptor possibly resulting from proteolytic cleavage of the receptor at a site close to the cell surface.
D000906:Antibodies / Q000032:analysis; D013956:Antithyroid Agents; D001681:Biological Assay; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D006111:Graves Disease / Q000097:blood; D006801:Humans; D008135:Long-Acting Thyroid Stimulator / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D009930:Organic Chemicals; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism; D011989:Receptors, Thyrotropin; D013972:Thyrotropin / Q000378:metabolism
D000906:Antibodies; D013956:Antithyroid Agents; D009930:Organic Chemicals; D011956:Receptors, Cell Surface; D011989:Receptors, Thyrotropin; C018995:long-acting thyroid stimulator inhibitor; D013972:Thyrotropin; D008135:Long-Acting Thyroid Stimulator