Studies on the mode of action of calciferol XXXII. Evidence for a 24(R),25(OH) 2-vitamin D 3 receptor in the parathyroid gland of the rachitic chick

Abstract

Summary Previous studies from a number of laboratories suggest a biological role for 24(R),25-dihydroxyvitamin D3 [24,25(OH)2D3] in bone mineralization, parathyroid hormone secretion and possibly intestinal calcium absorption. As a consequence we have initiated a search for a binding protein/receptor for 24,25(OH)2D3 analogous to that previously shown to exist in many tissues for 1,25-dihydroxyvitamin D3. Here we report for the first time the existence of a 24,25(OH)2D3 receptor/binding protein in the parathyroid glands of rachitic chicks. Incubation of a 105,000 x g supernatant of a 0.4 M KC1 extract of parathyroid gland chromatin with [3H]-24,25(OH)2D3 both before and after 5–20% sucrose density gradient centrifugation resulted in the detection of a receptor-like binding component with a mobility of 3.2–3.4 S. This putative 24,25(OH)2D3 receptor was shown to have ligand specificity for 24,25(OH)2D3 over 25-hydroxyvitamin D3 and to be a different macromolecular species than the 6 S binding protein for 25(OH)D3 which is present in the cytosol but not chromatin of the parathyroid gland.