JBC, Vol. 252, Issue 3, 1079-1083, Feb, 1977
Studies of binding of parathyroid hormone to a detergent-dispersed preparation from bovine kidney cortex plasma membranes
C. C. Malbon and J. E. Zull
Bovine kidney plasma membranes containing parathyroid hormone-sensitive
adenylate cyclase activity were dispersed with 1% Triton X-100 and
centrifuged at 150,000 X g for 2 h. Approximately 40% of the total membrane
protein was extracted by this procedure. The extraction greatly reduces the
fluoride-stimulated and the parathyroid hormone-sensitive adenylate cyclase
activity of the membranes and yields a supernatnat which binds biologically
active, tritiated parathyroid hormone. Hormone binding is stable for up to
15 h and has a linear dependence on protein concentration in the extract.
Binding of the labeled hormone at concentrations of 5 to 10 nM is inhibited
by preincubation with unlabeled min, and displays a dependence on
temperature, time, and pH. Binding specificity is maximal at physiological
pH, being inhibited by only the native hormone or its synthetic 1-34
NH2-terminal, biologically active fragment. Binding increases dramatically
at pH 6.0, but is nonspecific in character. Half-maximal inhibition of the
binding was achieved at 3.2 X 10(-7) M concentrations of the native hormone
and 5.0 X 10(-7) M concentrations of the synthetic 1-34 NH2-terminal
fragment. Calcium does not inhibit either total or specific binding.
Inhibition, kinetic, and pH dependence data suggest that the extracted
component(s) represent the parathyroid hormone binding protein(s) formerly
identified in particulate membrane preparations.