Characterization of the prolactin receptor in cell fractions from rat liver

[125I]Prolactin (PRL) was covalently cross-linked to its binding sites in subcellular fractions of female rat livers using NHSAB and UV irradiation. Analysis by non-reducing SDS-PAGE showed that all fractions with specifically bound radioactive hormone contained a major autoradiographic band (eliminated with unlabeled PRL) of similar electrophoretic mobility consistent with a MW of 36K for the receptor. In addition, microsomal membranes were treated with a zwitterionic detergent (CHAPS), solubilizing 30-60% of the specifically bound radioactivity. SDS-PAGE analysis of [125I]PRL cross-linked to CHAPS-soluble and CHAPS-insoluble material showed an autoradiographic band with a similar MW. These results suggest that prolactin receptors in different hepatocyte membranes are similar in MW and do not appear to be linked by disulfide bonds to other membrane proteins. Some of the binding sites appear to interact with membrane constituents in ways that affect their solubility by CHAPS.