谷胱甘肽与D型氨基酸非共价复合物的质谱

为了研究谷胱甘肽和D型氨基酸的非共价相互作用, 将一定化学剂量比的还原型谷胱甘肽与D-苯丙氨酸、D-组氨酸或D-谷氨酰胺在室温下混合后, 温育1 h, 使反应达到平衡. 电喷雾质谱测量结果表明, 在生理pH条件下, 谷胱甘肽可以和D 型氨基酸经反应生成非共价复合物. 串级质谱中的碰撞诱导解离(CID)以及紫外光谱进一步确认了非共价复合物的生成. 为了避免严重的离子化效率和质谱信号相互抑制作用, 对谷胱甘肽和D-谷氨酰胺的相互作用作了定量的评估. 配制一系列不同初始浓度的谷胱甘肽和D型氨基酸的混合溶液, 并用电喷雾质谱测定混合溶液中不同质点的质谱峰强度, 计算了谷胱甘肽与三个D型氨基酸结合形成的复合物的解离常数. 计算结果表明, 谷胱甘肽可以和D型氨基酸结合形成不同键合强度的非共价复合物, 其稳定性按照D-谷氨酰胺、D-苯丙氨酸、D-组氨酸的次序逐渐增大.

Probing Non-Covalent Complexes of Glutathione with D-Amino Acids by Mass Spectrometry

To investigate the non-covalent interaction between glutathione and D-amino acids, stoichiometric reduced glutathione (GSH) and three D-amino acids, including D-phenylalanine (D-Phe), D-histidine (D-His), and D-glutamine (D-Gln), were mixed respectively, and then incubated at room temperature for 1 h to reach equilibrium. The electrospray ionization mass spectrometry (ESI-MS) results indicated that glutathione and three D-amino acids could formnon-covalent complexes in physiological pH conditions, respectively. The binding of glutathione to D-amino acid was further confirmed by collision-induced dissociation (CID) in a tandem mass spectrometer. Additionally, the complexes exhibited different features and properties from the reactants in UV spectroscopy, which also confirmed the results of ESI-MS. To avoid distinct ionization efficiency discrepancy and signal suppression in ESI-MS measurements, the interaction between glutathione (GSH) and D-glutamine (Gln) was quantitatively evaluated. A series of samples with different initial concentrations of glutathione and D-amino acids were mixed, and then series of peak intensities for different species in the mixture were achieved by ESI-MS. The dissociation constants of three complexes formed by glutathione and D-amino acids were calculated. The calculation results revealed that the reduced tripeptide γ-glutathione could interact with D-amino acids to formnon-covalent complexes with different affinities, the stabilities of the three complexes increased gradually according to the order of D-glutamine, D-phenylalanine, and D-histidine.