INTERACTION OF CELL-MEMBRANE PROLACTIN RECEPTOR WITH ITS ANTIBODY

Antisera against a partially purified prolactin-receptor preparation derived from pregnant-rabbit mammary glands were generated in guinea pigs. On double immunodiffusion, each antiserum produced a single precipitin line with the prolactin receptors. The anti-receptor sera specifically inhibited the binding of 125I-labeled sheep prolactin to membrane particles and to highly purified prolactin receptors derived from the rabbit mammary glands. The same antisera had no effect on the binding of 125I-labeled insulin to the same membranes. These antisera did not bind or destroy prolactin. The binding of 125I-labeled prolactin to membrane particles derived from different tissues from a number of species was inhibited by the antisera, thus suggesting that the immunological determinants of the prolactin receptors are similar in various tissues derived from different species [rabbit, mouse, rat, human]. The factors in the antisera that were responsible for inhibiting the binding of 125I-labeled prolactin to its receptors were associated with the .gamma.-globulin fraction. 131I-labeled .gamma.-globulins derived from 1 antiserum apparently bound to membrane particles derived from mammary glands, and an increase in binding of .gamma.-globulin was accompanied by a decrease in binding of prolactin. Kinetic analyses of inhibition of 125I-labeled prolactin binding by antisera by using the methods of Lineweaver and Burk and Dixon revealed that the mechanism is a hyperbolic competitive inhibition. The demonstration of hormone-receptor-antibody complexes further favors this mechanism. The availability of anti-receptor sera should facilitate studies on the functional role and other biochemical, immunological and physiological properties of the prolactin receptors.