Parathormone receptor binding and the influence of membrane degradation of the hormone.
Concentration of receptor bound parathormone was determined using a labelled-antibody-membrane-assay (LAMA). 4.2-31.2 fmol PTH per mg membrane protein (0.42-3.12 fmol/tube) were bound at apparent PTH concentrations of 15.6-500 fmol/tube. Only 0.65%-3.2% of PTH could be detected at the receptor sites. The amount of free hormone was corrected for inactivation of intact immunologically reactive PTH and of intact biologically reactive PTH. Only after the latter correction were values for binding affinity (Kd = 1.1 x 10(-12) mol/mg) and number of binding sites (Bmax = 5.8 x 10(-14) mol/mg) obtainable. These results indicate that allowance must be made for loss of biological activity of hormone at membrane receptor sites if binding parameters are to be defined free of artifacts. Binding data may otherwise be misinterpreted as indicating negative cooperativity, heterogeneity of binding sites or multi-step reactions.
D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002642:Chick Embryo; D006041:Goats; D007668:Kidney / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000276:immunology / Q000378:metabolism*; D010527:Perissodactyla; D011956:Receptors, Cell Surface; D012756:Sheep
D010281:Parathyroid Hormone; D011956:Receptors, Cell Surface