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