Binding of bovine parathyroid hormone to surface receptors of cultured B-lymphocytes

Binding of parathyroid hormone onto B-lymphocytes is detected by the utilization of the labelled antibody membrane assay. The amount of parathyroid hormone bound to the receptor sites was depending on the quantity of cells in the incubation milieu. Each cell line showed typical characteristics in time course of parathyroid hormone binding and maximal receptor capacity. Fragmentation of intact parathyroid hormone, also varying with the cell line tested, was very rapid, even at 24°C. Within 20 min most of the cell lines destroyed 50% of the native hormone in the incubation mixture, indicating a fragmentation rate of up to 2.25 ng/min at 37°C. B_max and K_D for the different lymphocytes was 5.3–19 · 10¹¹ M and 1.8–18.5 · 10¹¹ M, respectively. These values are in the range of reported plasma concentrations and may therefore represent more physiological values for the capacity and affinity of membrane receptors.