Binding of somatomedins and insulin to plasma membranes prepared from rat and monkey tissue.

Particulate membranes prepared from a variety of monkey and rat tissues were shown to have specific binding sites for somatomedin A. Binding to talc on the other hand showed no specificity, and the sensitivity was less. The membrane-bound somatomedin A was displaced by somatomedin A in concentrations between 0.01 and 5 U/ml. Of the other hormones tested only insulin in high concentrations could interfere with the binding of labelled somatomedin A to tissue membranes. Membranes prepared from a number of rat and monkey tissues also contained binding sites for insulin. Somatomedin A could interfere with the binding of labelled insulin. No binding was observed for somatomedin B in the tissues studied.