THE EFFECTS OF SULPHYDRYL REAGENTS ON THE NEUTRALIZATION OF LATS BY HUMAN THYROID EXTRACTS

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Abstract
LATS [long-acting thyroid stimulator] is neutralized by an unknown antigenic substance in human thyroid tissue. This antigen was presumed to be a TSH receptor. This experiment examined whether SH reagents capable of altering the characteristics of TSH receptors in thyroidal crude membrane fractions caused an alteration in the LATS neutralization activity of the same fraction. Diamide (10-3 M) enhanced 125I-TSH binding to TSH receptors by increasing the binding affinity of the receptor and significantly increased the neutralization of LATS by the crude membrane fraction. Dithiothreitol (10-3 M) inhibited 125I-TSH binding by decreasing the affinity of the receptor and significantly decreased the neutralization of LATS by the fraction. Evidently, TSH receptors and the thyroidal factor capable of neutralizing LATS share a common property in terms of the effects of SH reagents. This is compatible with the idea that the LATS neutralizing activity of thyroidal crude membrane fraction is due to binding by the TSH receptor or its fragments.