Kidney Membrane Binding of Native Parathyroid Hormone Compared to Binding of Its Synthetic 1–34 Fragment

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Abstract
Kidney membrane binding of tritiated native parathyroid hormone (PTH) was compared to that of its active fragment 1–34 PTH. Native hormone specific binding is transient and disappears rapidly (~ 30 minutes) at 37°C but is stable up to 2 hours at 0°C. The rate of binding loss appears relatively independent of the amount of hormone-receptor complex or of the amount of cold PTH in the medium. Loss of specific binding is also seen with iodinated PTH. Loss of specific binding of native PTH does not appear to be the result of enzymatic degradation of the hormone since significant amounts of intact hormone are present, both bound to membranes and in the medium after incubation. Biologically active tritiated 1–34 PTH was prepared and its binding studied. Tritiated 1–34 PTH binds specifically to isolated membranes, and both total and specific binding is stable for at least one hour at room temperature. The pH dependence for binding of 1–84 PTH and its activation of adenylyl cyclase are very similar, but differ from that reported for specific binding of 1–34 PTH. These results suggest that the interaction of native PTH with kidney cells may be more complex than that of its 1–34 fragment.