COMPARISON OF BINDING OF BOVINE AND HUMAN THYROID-STIMULATING HORMONE TO RECEPTOR SITES ON HUMAN THYROID MEMBRANES

Abstract

The binding of ¹²⁵I-labelled bovine TSH (bTSH) to a wide range of human thyroid membrane preparations was compared with that of ¹²⁵I-labelled human TSH (hTSH). Much higher binding percentages were obtained with the ¹²⁵I-labelled bTSH. This was because the receptors had a higher binding affinity for bTSH than for hTSH. No differences in tracer purity, nor differences in optimal conditions for the binding of bTSH or hTSH, nor tracer degradation contributed significantly to the better binding of ¹²⁵I-labelled bTSH. Good correlation was found between binding percentages for ¹²⁵I-labelled bTSH and ¹²⁵I-labelled hTSH over the range of thyroid specimens. Useful information on human TSH receptors is, therefore, obtainable from binding studies with ¹²⁵I-labelled bTSH. The TSH displacement curves yielded linear Scatchard plots whenever the tracer and displacing hormones were of the same species. The data were, therefore, consistent with a simple binding reaction between TSH and a single set of independent receptor sites.