Abstract
The presence of lactogenic and somatogenic binding sites in intact microsomal membranes and in detergent-solubilized microsomal membrane preparations of female rat liver has been studied by affinity cross-linking-SDS/polyacrylamide-gel electrophoresis. In microsomal membrane preparations an Mr 40,000 lactogenic binder is present which is not disulphide-linked to another protein. Triton X-100 solubilization of membranes results in the appearance of three lactogenic 125I-human growth hormone (125I-hGH) binders with Mr values of 87,000, 40,000 and 35,000, and one somatogenic 125I-hGH binder with Mr 32,000. Treatment of rats with oestrogen increased the amount of lactogenic and somatogenic binding species in liver. The lactogenic binding sites are present as one entity in Triton X-100-solubilized preparations, clearly separated from the somatogenic binder as analysed by gel chromatography. Furthermore, 125I-hGH interacts with an Mr 95,000 somatogenic binder in membrane preparations to which the hormone can be cross-linked only following Triton X-100 solubilization.