Fast proton exchange in histidine: measurement of rate constants through indirect detection by NMR spectroscopy.
Owing to its imidazole side chain, histidine participates in various processes such as enzyme catalysis, pH regulation, metal binding, and phosphorylation. The determination of exchange rates of labile protons for such a system is important for understanding its functions. However, these rates are too fast to be measured directly in an aqueous solution by using NMR spectroscopy. We have obtained the exchange rates of the NH3(+) amino protons and the labile NH(ε2) and NH(δ1) protons of the imidazole ring by indirect detection through nitrogen-15 as a function of temperature (272 K<T<293 K) and pH (1.3<pH<4.9) of uniformly nitrogen-15- and carbon-13-labeled L-histidine⋅HCl⋅H2O. Exchange rates up to 8.5×10(4) s(-1) could be determined (i.e., lifetimes as short as 12 μs). The three chemical shifts δH(i) of the invisible exchanging protons H(i) and the three one-bond scalar coupling constants (1)J(N,H(i)) could also be determined accurately.
Ecole Normale Supérieure, Département de Chimie, 24 rue Lhomond, 75231 Paris Cedex 05 (France), Fax: (+33) 1-44-32-24-02; Université Pierre et Marie Curie, Paris (France); UMR 7203, CNRS, Paris (France).
Akansha Ashvani
AA
Sehgal
Luminita
L
Duma
Geoffrey
G
Bodenhausen
Philippe
P
Pelupessy
D000596:Amino Acids; D002384:Catalysis; D006639:Histidine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011522:Protons
D000596:Amino Acids; D011522:Protons; D006639:Histidine
NMR spectroscopy; amino acids; exchange rate constants; protonation