A morphologic analysis of insulin binding sites in isolated rat liver nuclei.

Under conditions which demonstrated a high degree of specific 125I-insulin binding to purified plasmalemma, no specific binding could be found in freshly prepared nuclei. Analysis of light and electron microscope radioautographs of nuclei incubated with 125I-insulin with and without additional excess unlabeled insulin also failed to provide any evidence for 125I-insulin binding to rat liver nuclei in vitro. It is concluded that current methods are too insensitive to detect insulin receptors in nuclei (if indeed such receptors exist in this organelle to any appreciable extent.