title: A proton-nuclear-magnetic-resonance study of human somatotropin (growth hormone). Assignment and properties of the histidine residues.
abstract: The 1H-n.m.r. spectra of human somatotropin (growth hormone) show perturbed peaks from individual aromatic and aliphatic apolar residues, characteristic of a specifically folded globular structure. The imidazole C-2-H resonances of the histidine residues (at positions 18, 21 and 151 in the somatotropin sequence) were individually resolved, and their titration behaviour in the pH range 1.2-11.5 was investigated. The imidazole C-2-H resonance of histidine-151 is assigned, by comparison of its titration behaviour in human somatotropin and desamido-somatotropin (Asn-152 leads to Asp-152). The C-2-H resonances of all three histidine residues are assigned, by comparison of their relative deuterium-exchange rates (determined by n.m.r.) and the relative tritium-exchange rates of the histidine residues (determined by tryptic digestion of tritiated human somatotropin and reversed-phase high-pressure liquid-chromatographic separation of the histidine-containing tryptic peptides). There is evidence that histidine-18 forms an ion-pair bond with a glutamic acid or aspartic acid residue. The globular structure does not appear to change from pH3 to 11.5, though there is evidence for an unfolding of a region of the structure (involving histidine-21 and a tyrosine residue) below pH3.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002851:Chromatography, High Pressure Liquid; D003903:Deuterium; D013006:Growth Hormone; D006639:Histidine / Q000032:analysis*; D006801:Humans; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010446:Peptide Fragments / Q000032:analysis; D014316:Tritium; D014357:Trypsin
chemical_list: D010446:Peptide Fragments; D014316:Tritium; D006639:Histidine; D013006:Growth Hormone; D003903:Deuterium; D014357:Trypsin