Catalytic activity of anti-thyroglobulin antibodies.
Thyroglobulin (Tg)-specific autoantibodies from a patient with Hashimoto's thyroiditis hydrolyzed radiolabeled Tg, shown by production of several smaller sized products on SDS electrophoresis gels. The apparent Km value for Tg was in the nanomolar range, a property typical of an Ab combining site. The Tg antibodies also hydrolyzed tripeptide-methylcoumarinamide (MCA) substrates with lower affinity, displaying a preference for Arg-MCA and Lys-MCA containing conjugates. The hydrolysis of one of these conjugates, Pro-Phe-Arg-MCA, was inhibited competitively by Tg, suggesting a catalytic site located in the Ab combining site. In control experiments, 1) the hydrolytic activities were removed by immunoadsorption with immobilized anti-human IgG; 2) IgG depleted of the Tg-specific Abs by affinity chromatography did not display Tg and Pro-Phe-Arg-MCA hydrolyzing activities; and 3) the peptide-MCA hydrolyzing activity tracked exactly with the 150-kDa IgG peak on a gel filtration column run in denaturing solvent (6 M guanidine chloride).
Li
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Department of Anesthesiology, University of Nebraska Medical Center, Omaha 68198.
Paul
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Tyutyulkova
S
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Kazatchkine
M D
MD
Kaveri
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S
D000595:Amino Acid Sequence; D017151:Antibodies, Catalytic / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D006801:Humans; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000276:immunology; D013379:Substrate Specificity; D013954:Thyroglobulin / Q000276:immunology*; D013967:Thyroiditis, Autoimmune / Q000276:immunology
D017151:Antibodies, Catalytic; D001323:Autoantibodies; D009842:Oligopeptides; C006606:anti-thyroglobulin; D013954:Thyroglobulin