Sehgal Akansha Ashvani, Duma Luminita, Bodenhausen Geoffrey, Pelupessy Philippe
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).
Chemistry. 2014 May 19;20(21):6332-8. doi: 10.1002/chem.201304992. Epub 2014 Apr 9.
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.
由于其咪唑侧链，组氨酸参与各种过程，如酶催化、pH调节、金属结合和磷酸化。确定这种体系中不稳定质子的交换速率对于理解其功能很重要。然而，这些速率太快，无法通过核磁共振光谱法在水溶液中直接测量。我们通过以氮-15作为间接检测手段，获得了均匀标记氮-15和碳-13的L-组氨酸·HCl·H₂O中NH₃⁺氨基质子以及咪唑环中不稳定的NH(ε2)和NH(δ1)质子的交换速率，该速率是温度（272 K < T < 293 K）和pH（1.3 < pH < 4.9）的函数。可以确定高达8.5×10⁴ s⁻¹的交换速率（即寿命短至12 μs）。还可以准确测定不可见交换质子H(i)的三个化学位移δH(i)和三个一键标量耦合常数(¹J(N,H(i)))。
