The effect of S-adenosyl methionine on the TSH receptor function in human thyroid tissue: Increase in binding of TSH and decrease in adenylate cyclase coupling.

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Abstract
To determine the effects of S-Adenosyl methionine (AdoMet) on TSH receptor function and adenylate cyclase coupling, human thyroidal crude membrane fraction was pretreated with AdoMet and with S-Adenosyl homocysteine (AdoHcy), separately or in combination. 125I-TSH binding to the pretreated membrane and adenylate cyclase activity of the membrane were examined. In contrast to the reported effect of AdoMet on the decrease in GH [growth hormone] binding to lactogenic receptor, AdoMet 0.5 .mu. mol/ml significantly increased the binding of TSH to the receptor by increasing the affinity of the binding, while it decreased the coupling of adenylate cyclase significantly. The effect of AdoMet was partially counteracted by the pretreatment of the membrane with AdoHcy. This effect of AdoMet is very similar to that of diamide previously reported. The result implies that the effect is due to an alteration in the tertiary structure of receptor protein triggered by methylation.