A “Carboxyl Terminal” Clinical R Adioim Muno Assay for Parathyroid Hormone with Apparent Recognition Preference for the Intact Hormone

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Abstract
A radioimmunoassay for Parathyroid Hormone which is used in a clinical setting was characterized by (1) immunoreactivity with various synthetic fragments of the hormone, (2) serum parathyroid hormone response to oral calcium intake in normocalcemic calcium stone-formers, and (3) ability to detect fragments of parathyroid hormone secreted by abnormal human parathyroid tissue in vitro. Although almost all of the recognition sites for the antiserum were within the 53-84 carboxyl terminal amino acid sequence of the hormone, the radioimmunoassay mainly detected the "intact" hormone rather than the carboxyl terminal fragment(s) which most "carboxyl-terminal" assays of parathyroid hormone are claimed to preferentially detect. Differences in tertiary structure between the intact hormone and its fragments probably account for the relative inability of this antiserum to detect the carboxyl terminal fragment(s).