Characterization of hepatic lactogen receptor. Subunit composition and hydrodynamic properties

The structure of the membrane-bound and Triton X-100-solubilized female rat liver prolactin receptor has been studied by affinity cross-linking/sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel filtration, and sucrose/H2O and sucrose/D2O density gradient centrifugation. Hydrodynamic characterization revealed that the 125I-human growth hormone receptor-detergent complex represents a molecular species with a Stokes radius of 61 A, a sedimentation coefficient of 5.0 s, and a calculated molecular weight of 158,000. The molecular weight of the receptor was calculated to be 92,000. Three lactogenic hormone-binding species with Mr values of 87,000, 40,000, and 35,000, respectively, were repeatedly found when detergent-solubilized preparations were analyzed using an affinity cross-linking technique. Estrogen treatment of female rats increased the intensity of these bands. Occasionally, an Mr 165,000 hormone-binding species was also found. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis studies (first dimension, nonreducing; second dimension, reducing) demonstrated that disulfide- and nondisulfide-linked hormone-binding species with Mr values of 40,000 and 35,000 are contained within the Mr 87,000 species. It is concluded that the Triton X-100-solubilized female rat liver prolactin receptor has a molecular weight of about 90,000. This molecular species contains Mr 40,000 and Mr 35,000 hormone-binding subunits. It cannot be determined whether these subunits are combined with each other or with as yet undetected subunit(s) to make up the Mr 90,000 species, or whether each one of these subunits is a proteolytic fragment of the Mr 90,000 species.