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Immunological properties of synthetic human parathyroid hormone: effect of deamidation at position 76
Synthetic human parathyroid hormone with asparagine at residue 76 (hPTH 1-84 (Asn 76], as seen in the native peptide, was labelled with 125I and used as radioligand in radioimmunoassays. It was found to give better binding to antibodies raised against extracted human parathyroid hormone (hPTH 1-84) than 125I-labelled native hPTH 1-84. It was also superior in the study of the antigenic determinants of these antisera by the use of calibration curves with synthetic fragments of the human parathyroid hormone. The immunological properties of synthetic hPTH 1-84 (Asn 76) were examined in four region-specific labelled antibody assays and compared with those of native hPTH 1-84 and with an analogue of parathyroid hormone 1-84 with aspartic acid at residue 76 (hPTH 1-84 (Asp 76]. The synthetic hPTH 1-84 (Asn 76) and the native hormone behaved similarly in all four assays which were specific to the amino-, mid- and carboxy-regions of human parathyroid hormone. The synthetic hPTH 1-84 (Asp 76) also behaved similarly in the amino- and both mid-region-specific assays but was markedly less reactive in the carboxy-region-specific assay. This demonstrated that deamidation at residue 76 of human parathyroid hormone affects the immunological properties of the molecule. This also provides an explanation for a previous observation that in a carboxy-terminal-specific assay the native 53-84 peptide (hPTH 53-84) was more reactive than a synthetic preparation of 53-84 with aspartic acid at residue 76. It is concluded that synthetic hPTH 1-84 (Asn 76) is a satisfactory standard for the immunoassay of human parathyroid hormone and is useful as a radioligand when labelled with 125I.
Synthetic human parathyroid hormone with asparagine at residue 76 (hPTH 1-84 (Asn 76], as seen in the native peptide, was labelled with 125I and used as radioligand in radioimmunoassays. It was found to give better binding to antibodies raised against extracted human parathyroid hormone (hPTH 1-84) than 125I-labelled native hPTH 1-84. It was also superior in the study of the antigenic determinants of these antisera by the use of calibration curves with synthetic fragments of the human parathyroid hormone. The immunological properties of synthetic hPTH 1-84 (Asn 76) were examined in four region-specific labelled antibody assays and compared with those of native hPTH 1-84 and with an analogue of parathyroid hormone 1-84 with aspartic acid at residue 76 (hPTH 1-84 (Asp 76]. The synthetic hPTH 1-84 (Asn 76) and the native hormone behaved similarly in all four assays which were specific to the amino-, mid- and carboxy-regions of human parathyroid hormone. The synthetic hPTH 1-84 (Asp 76) also behaved similarly in the amino- and both mid-region-specific assays but was markedly less reactive in the carboxy-region-specific assay. This demonstrated that deamidation at residue 76 of human parathyroid hormone affects the immunological properties of the molecule. This also provides an explanation for a previous observation that in a carboxy-terminal-specific assay the native 53-84 peptide (hPTH 53-84) was more reactive than a synthetic preparation of 53-84 with aspartic acid at residue 76. It is concluded that synthetic hPTH 1-84 (Asn 76) is a satisfactory standard for the immunoassay of human parathyroid hormone and is useful as a radioligand when labelled with 125I.