Immunological studies on parathyroid hormone: characterization of antisera against synthetic 1-34 human parathyroid hormone and evidence that position 30 in human parathyroid hormone is aspartic acid.

Radioimmunoassays for the measurement of the 1--34 human parathyroid hormone fragment (1--34 hPTH) were developed using antisera raised in rabbits against synthetic 1--34 hPTH-N (amino acid sequence proposed by Niall). Binding of 125I-labelled 1--34 hPTH-N to these antisera was optimal at pH 5-5. Limits of detection varied between 25 and 200 pg/ml. Cross-reactivity of 1--34 bovine PTH was substantial in all assays; 1--34 hPTH-B (structure proposed by Brewer), 1--84 hPTH and 1--29 hPTH cross-reacted only with antisera from one animal. 1--29 Human PTH was obtained from partial hydrolysis of both 1--84 hPTH and 1--34 hPTH-N. Production of 1--29 hPTH from 1--84 hPTH was demonstrated by comparison of the elution profiles of the reaction product and 1--29 bovine PTH on Sephadex G-50. Thus, evidence was obtained that position 30 in native hPTH is occupied by an aspartic acid residue.