Characterization of the insulin and somatomedin-C receptors in human placental cell membranes.

Abstract

ABSTRACT Human placentas have been used to further investigate the binding of insulin and somatomedin to cell membrane receptors. Conditions for optimal binding of 125I-insulin were defined for both participate membrane preparations and membranes solubilized in Triton X-100. Human placental membranes are a rich source of high affinity insulin receptors. As in previous studies with rat liver and fat cell preparations, only somatomedin and proinsulin were effective competitors for binding to the insulin receptor. These findings were used to define the optimal conditions for a competitive binding assay for insulin and insulin-like peptides. This assay had threshold sensitivities of 10 μU/ml for insulin and less than 0.1 U/ml for somatomedin. Incubation at 4 C for 15–18 hr essentially eliminated proteolytic degradation of the labeled hormone and led to strikingly better binding than was observed at higher temperatures. A highly purified preparation of somatomedin-C labeled with radioactive iodine was found to...