Characterization of Two Anti-Human Parathyrin Antisera1)

Summary: Two anti-human parathyrin antisera were raised in sheep. These were characterized by radioimmunoassay using two commercially available bovine parathyrin preparations and one synthetic human parathyrin fragment (sequence 42—55 (42-Tyr)) for radioiodination. In addition, four synthetic human parathyrin fragments (sequences 1—34, 32—43, 44—68, 53^84), one bovine parathyrin peptide (sequence 28—48) and a human parathyrin Standard from a tissue culture contaiiiing the intact hormpne were utilized in a competitive Inhibition assay against the two radiolabelled bovine parathyrin preparations. On column chromatography, both tracers revealed a diffefence in molecular weight, which is believed to be related to the extraction technique. The sequence fragment 44—68 of human parathyrin had the highest affinity for the two antisera when using the srnäller molecular weight tracer and there were no qualitative changes observed in the presence of plasma. Using the higher molecular weight tracer, the addition of plasma to one of the antisera resulted in a higher affinity for the sequence fragment 1—34 of human parathyrin cömpared tö that of intact parathyrin. Antiserum frpm a second sheep remained specific only for the mid-region (sequence 44-r68) of the parathyrin molecüle independent of the tracer used. Due to the antiserum's constant characteristic, it revealed a high reliability for the discrimination between plasma parathyrin levels in normal probands and in patients with hyperparathyroidism. Our data demonstrate that the specificity of the radioimmunoassay for human parathyrin is not exclusively dependent the antibody spurce, but also on the tracer preparation and th