Water-Soluble Prolactin Receptors from Porcine Mammary Gland

Abstract

Two types of prolactin receptors were identified in sow mammary gland. When light membranes were prepared on a discontinuous sucrose gradient (0.3 and 1.7 M) and then diluted and washed with 0.3 M sucrose solution, a large amount (about 50%) of receptors were released from membranes and appeared in the supernatant fraction. These two forms (hydrophobic and water-soluble) of receptors were characterized as having the same binding specificity for lactogenic hormones and a similar affinity constant for ovine prolactin (K _a ~ 10–12 × 10⁹ M ^-1). Polyclonal antibodies and one monoclonal (mAb MHO) antibody, obtained against partially purified prolactin receptors from rabbit mammary gland, cross-reacted effectively with sow mammary receptors. They completely inhibited the specific binding of [¹²⁵I]oPRL to membrane and water-soluble receptors. The present studies indicate that the two types of sow prolactin receptors could represent the same molecular entity and confirm that prolactin receptors from rabbit and sow mammary gland exhibit numerous antigenic similarities.