The effects of sulphydryl reagents on the neutralization of LATS by human thyroid extracts

LATS has already been shown to be neutralized by an unknown antigenic substance in human thyroid tissue. This antigen has been presumed to be a TSH receptor. To examine this hypothesis, we sought to determine 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) which was shown to enhance 125I-TSH binding to TSH receptors by increasing the binding affinity of the receptor, significantly increased the neutralization of LATS by the crude membrane fraction. Dithiothreitol (10(-3) M) which was shown to inhibit 125I-TSH binding by decreasing the affinity of the receptor, significantly decreased the neutralization of LATS by the fraction. This indicates that TSH receptors and the thyroidal factor capable of neutralizing LATS share a common property in terms of the effects of SH reagents and 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.