title: Evidence that the amino-terminal composition of non-(1-84) parathyroid hormone fragments starts before position 19.
abstract: BACKGROUND
  Non-(1-84) parathyroid hormone (PTH) fragments are large C-terminal fragments of PTH with a partially preserved N-terminal structure. They differ from other C-terminal PTH fragments, which do not have an N-terminal structure and do not react in intact PTH assays. We aimed to identify the minimal N-terminal structure common to all non-(1-84) PTH fragments.
  
  
  METHODS
  Sera obtained from six healthy individuals and six patients with primary hyperparathyroidism, and six serum pools from dialysis patients with different PTH concentrations were fractionated by HPLC and analyzed by four different PTH assays. Each assay was characterized by saturation analysis of its detection antibody and capacity to react with different PTH fragments. Human PTH(1-84) [hPTH(1-84)] calibrators were normalized to an in-house hPTH(1-84) calibrator.
  
  
  RESULTS
  The cyclase-activating PTH (CA-PTH) assay had an early (1, 2,) epitope and reacted only with hPTH(1-84). The other assays had epitopes in region (13-34). Total and intact PTH assays had epitopes proximal to position 18 and reacted equally well with hPTH(1-84) and hPTH(7-84), and the Elecsys PTH assay had an epitope distal to position 19, being saturable by hPTH(18-48) and also reacting with [Tyr(34)]hPTH(19-84). The HPLC profiles obtained with these assays showed that non-(1-84) PTH fragments did not react in the CA-PTH assay, as expected. The amount of non-(1-84) PTH detected by the other three assays was similar when the assay results were normalized to a common calibrator.
  
  
  CONCLUSIONS
  The results suggest that the amount of non-(1-84) PTH detected by epitopes proximal or distal to position 19 of the PTH structure is identical, indicating a common minimum structure starting before position 19. This in turn points to a probable high-affinity interaction with the C-PTH receptor, as observed previously with [Tyr(34)]hPTH(19-84) in various cell lines and in mouse osteocytes with PTH/PTHrP type I receptor ablation.
authors.affiliation: Centre de Recherche, Centre Hospitalier de l'Université de Montréal, Hôpital Saint-Luc, Université de Montréal, Montréal, Québec H2X 1P1, Canada. rechcalcium.chum@ssss.gouv.qc.ca
authors.forename: Pierre
authors.initials: P
authors.lastname: D'Amour
authors.forename: Jean-Hugues
authors.initials: JH
authors.lastname: Brossard
authors.forename: Agnès
authors.initials: A
authors.lastname: Räkel
authors.forename: Louise
authors.initials: L
authors.lastname: Rousseau
authors.forename: Caroline
authors.initials: C
authors.lastname: Albert
authors.forename: Tom
authors.initials: T
authors.lastname: Cantor
mesh_terms: D002138:Calibration; D000939:Epitopes; D006801:Humans; D006961:Hyperparathyroidism / Q000097:blood; D007118:Immunoassay; D010281:Parathyroid Hormone / Q000097:blood / Q000737:chemistry* / Q000276:immunology; D010446:Peptide Fragments / Q000097:blood / Q000737:chemistry* / Q000276:immunology
chemical_list: D000939:Epitopes; D010281:Parathyroid Hormone; D010446:Peptide Fragments; C040288:amino-terminal parathyroid hormone