title: Hydrogen-exchange kinetics of the indole NH proton of the buried tryptophan in the constant fragment of the immunoglobulin light chain.
abstract: The constant fragment of the immunoglobulin light chain (type lambda) has two tryptophyl residues at positions 150 and 187. Trp-150 is buried in the interior, and Trp-187 lies on the surface of the molecule. The hydrogen-deuterium exchange kinetics of the indole NH proton of Trp-150 were studied at various pH values at 25 degrees C by 1H nuclear magnetic resonance. Exchange rates were approximately first order in hydroxyl ion dependence above pH 8, were relatively independent of pH between pH 7 and 8, and decreased below pH 7. On the assumption that the exchange above pH 8 proceeds through local fluctuations of the protein molecule, the exchange rates between pH 7 and 8 through global unfolding were estimated. The exchange rate constant within this pH range at 25 degrees C thus estimated was consistent with that of the global unfolding of the constant fragment under the same conditions as those reported previously [Kikuchi, H., Goto, Y., & Hamaguchi, K. (1986) Biochemistry 25, 2009-2013]. The activation energy for the exchange process at pH 7.8 was the same as that for the unfolding process by 2 M guanidine hydrochloride. The exchange rates of backbone NH protons were almost the same as that of the indole NH proton of Trp-150 at pH 7.1. These observations also indicated that the exchange between pH 7 and 8 occurs through global unfolding of the protein molecule and is rate-limited by the unfolding.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biology, Faculty of Science, Osaka University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kawata
authors.forename: Y
authors.initials: Y
authors.lastname: Goto
authors.forename: K
authors.initials: K
authors.lastname: Hamaguchi
authors.forename: F
authors.initials: F
authors.lastname: Hayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Kyogoku
mesh_terms: D001536:Bence Jones Protein; D003903:Deuterium; D006801:Humans; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D007147:Immunoglobulin Light Chains; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010206:Papain; D011487:Protein Conformation; D011489:Protein Denaturation; D011522:Protons; D014364:Tryptophan
chemical_list: D007147:Immunoglobulin Light Chains; D011522:Protons; D006859:Hydrogen; D014364:Tryptophan; D001536:Bence Jones Protein; D003903:Deuterium; D010206:Papain