Isolation, Characterization, and Regulation of the Prolactin Receptor

The prolactin, or lactogenic hormone, receptor has been purified (∼ 80%) from lactating mouse liver and human term placenta by the nondenaturing zwitterionic detergent 3-[(3-cholamidopropyl) -dimethylammonio] -1-propane sulfonate and a prolactin affinity column. The isolated “core-binding unit” has a molecular weight of 37,000±2,000 daltons. It retains the specificity for lactogenic hormones and binds prolactin with an affinity (Ka = 2 to 6×109M−1) similar to that of the receptor as it occurs in its membranous environment (Ka = 3 to 5×109M−1). Whether this “core-binding unit” exists on the cell surface in a cryptic or active form is influenced greatly by its association with other membrane proteins and the concentration of phosphatidylcholine within its local membranous environment.