Abstract
Prolactin iodinated by lactoperoxidase method showed immunologically, electrophoretically and biologically similar properties to native prolactin and possessed enough specific radioactivity for receptor studies.125I-prolactin was incubated with mouse mammary tissues at 8 days of lactation. Both binding and release of125Iprolactin depended on incubation time and temperature and were maximal at 37°C. Michaelis constant was estimated to be 1.4×10-9 M from Lineweaver-Burk plot and to be 1.2×10-9 M from mid-value of the dose-response curve for displacement with native prolactin. Total number of binding sites for prolactin was 1.38×10-15 mole per mg weight of tissue. Ovine prolactin, human growth hormone and human placental lactogen competed with 125I-prolactin and dose-response curves for these three hormones were all parallel. These results suggest the existence of a specific receptor site with high affinity for prolactin in lactating mouse mammary glands.
