Bella, Francis P. Di

Biologically active 125 I-labeled bovine parathyroid hormone (prepared by electrolytic iodination) and its synthetic NH 2 -terminal (1-34) biologically active fragment bound rapidly and specifically to a purified plasma membrane preparation from bovine renal cortex. Binding of labeled intact hormone or labeled NH 2 -terminal (1-34) peptide was inhibited competitively by unlabeled (1-34) peptide in the same range of concentrations that activated renal cortical 3′:5′-adenylate cyclase (EC 4.6.1.1) in these membranes. The concentrations of synthetic (1-34) peptide for half-maximal inhibition of binding of labeled hormone as well as half-maximal activation of the enzyme were about 0.6 μM (2.5 μg/ml). Therefore it is likely that the binding activity studied represents a physiologically important renal receptor for parathyroid hormone. Biologically inactive (oxidized) forms of parathyroid hormone and (1-34) NH 2 -terminal peptide as well as calcitonin, glucagon, insulin, and epinephrine failed to competitively inhibit the binding of labeled (1-34) parathyroid hormone or activate adenylate cyclase in the renal cortical membrane preparation. Observations with the NH 2 -terminal (1-34) biologically active fragment of parathyroid hormone suggest that the COOH-terminal region of the molecule is not required for receptor binding.