title: Proton nuclear magnetic resonance study of the histidine residues of pituitary bovine growth hormone.
abstract: The pKa value of histidines 20, 22 and 170 of pituitary bovine growth hormone (pbGH) and their C2H deuterium exchange rates have been determined by high-resolution 1H-NMR spectroscopy. Partial assignment of these parameters indicate that His-170 is a surface residue with a half-life for deuterium exchange at the C2H position of approx. 36 h and a pKa value of 5.68 +/- 0.11. A reversible conformational change of pbGH has also been characterized in terms of the involvement of either histidines 20 or 22. At or near physiological pH values, one of these residues is expelled from a buried, hydrophobic position to become fully solvent-exposed. The disparity in pKa values between histidines 20 and 22 (4.67 +/- 0.20 and 5.94 +/- 0.10, in some combination) has been shown by computer modeling, to be compatible with these residues residing in an alpha-helical region of the protein.
authors.affiliation: Department of Pharmaceutical Sciences, University of Arizona, Tucson.
authors.forename: N E
authors.initials: NE
authors.lastname: MacKenzie
authors.forename: S M
authors.initials: SM
authors.lastname: Plaisted
authors.forename: D N
authors.initials: DN
authors.lastname: Brems
mesh_terms: D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D013006:Growth Hormone / Q000648:ultrastructure*; D006639:Histidine; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D011487:Protein Conformation
chemical_list: D006639:Histidine; D013006:Growth Hormone