title: Proton NMR studies of the biologically active 1-34 fragment of bovine parathyroid hormone: examination of a structural model.
abstract: Proton NMR spectra of the biologically active 1-34 fragment of bovine parathyroid hormone (bPTH) were studied as a function of pH over the range of pH 4 to 10, in buffer and in 6 M guanidine DC1. One of the histidine C-2 peaks titrated normally, with a pKa value of 6.8, but the other two histidines in this peptide had pKa values of 6.3. Denatured PTH showed only one histidine C-2 peak with a pKa of 6.7. An aliphatic peak identified as due to either a methionine or a glutamine residue also shifted with pH, and the pKa for this shift was 6.3. Finally, small but significant upfield shifts in the methyl and methylene resonances were observed as a function of pH, and when compared to the denatured peptide. These results indicate that the N-terminal domain of native PTH has considerable structure in solution, and are consistent with a theoretical model for the folding of this peptide.
mesh_terms: D000818:Animals; D002417:Cattle; D006639:Histidine; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008961:Models, Structural; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D011487:Protein Conformation; D019379:Teriparatide
chemical_list: D010281:Parathyroid Hormone; D010446:Peptide Fragments; D019379:Teriparatide; D006639:Histidine