Hydrogen-exchange kinetics of the indole NH proton of the buried tryptophan in the constant fragment of the immunoglobulin light chain

Journal Article · Tue Jan 12 00:00:00 EST 1988 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00401a052· OSTI ID:5302166

Kawata, Y; Goto, Y; Hamaguchi, K; Hayashi, F; Kobayashi, Y; Kyogoku, Y

The constant fragment of the immunoglobulin light chain (type lambda) has two trytophyl 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 Trp-150 were studied at various pH values at 25/sup 0/C by /sup 1/H 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/sup 0/C thus estimated was consistent with that of the global unfolding of the constant fragment under the same conditions as those reported previously. 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.l. 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. At around pH 9, on the other hand, the activation energy for the exchange process of the indole NH proton of Trp-150 was smaller than that for the unfolding process, and the exchange rates differed according to the different signals of backbone NH protons. These findings together with the pH dependence of the rate constant indicated that exchange due to local fluctuations is predominant above pH 8.

• Research Organization: Osaka Univ., Toyonaka, Japan
• OSTI ID: 5302166
• Journal Information: Biochemistry; (United States), Vol. 27:1
• Country of Publication: United States
• Language: English

Related Subjects

62 RADIOLOGY AND NUCLEAR MEDICINE
IMMUNOGLOBULINS
ISOTOPIC EXCHANGE
NUCLEAR MAGNETIC RESONANCE
ACTIVATION ENERGY
DEUTERIUM COMPOUNDS
MOLECULAR STRUCTURE
PH VALUE
PROTONS
TRYPTOPHAN
AMINO ACIDS
AROMATICS
AZAARENES
AZOLES
BARYONS
CARBOXYLIC ACIDS
ELEMENTARY PARTICLES
ENERGY
FERMIONS
GLOBULINS
HADRONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
INDOLES
MAGNETIC RESONANCE
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PROTEINS
PYRROLES
RESONANCE
550601* - Medicine- Unsealed Radionuclides in Diagnostics