CHARACTERIZATION OF THE SPECIFIC BINDING OF PROLACTIN TO BINDING SITES IN THE SEMINAL VESICLE OF THE RAT

Abstract

The binding of ovine prolactin to the seminal vesicles of the rat has been characterized and found to be a saturable process, dependent upon time, temperature, protein concentration of the seminal vesicle and divalent ions. Its specificity was similar to that reported for prolactin binding to other organ preparations. Time and temperature studies of the specific binding revealed that equilibrium was reached after 16 h at 5 °C or 4 h at 19 °C. Non-specific binding was also dependent on time and temperature. This parameter has been reported to comprise up to 70% of the total binding to various organ-binding sites, but it fell to below 20% after 48 h at 19 °C, thus demonstrating the high degree of specificity required of target organ receptors. From degradation studies it was evident that no damage occurred to the free hormone during incubation for up to 70 h at 5 °C or 16 h at 19 °C. However, there seems to be a difference in the susceptibility of bound and free ovine prolactin to damage during incubation: after 40 h at 19 °C the hormone in the supernatant fraction had lost 85% of its binding ability, whereas a high level of specific binding was evident in the pellet. A Scatchard plot of competitive binding studies revealed two classes of binding sites, of which the high-affinity, low-capacity site was similar to that reported previously and consistent with a physiological receptor for prolactin in the seminal vesicle of the rat.