Yoo Ellie Jung Hwa, Feketeová Linda, Khairallah George N, O'Hair Richard A J
School of Chemistry, University of Melbourne, Victoria 3010, Australia.
Eur J Mass Spectrom (Chichester). 2011;17(2):159-66. doi: 10.1255/ejms.1115.
The intrinsic methylating abilities of the known biological methylating zwitterionic agents, dimethylsulfonioacetate (DMSA), (CH(3))(2)S⁺CH(2)CO(2)(-) (1) and glycine betaine (GB), (CH(3))(3)N⁺CH(2)CO(2)(-) (2), have been examined via a range of gas phase experiments involving collision-induced dissociation (CID) of their proton-bound homo- and heterodimers, including those containing the amino acid arginine. The relative yields of the products of methyl cation transfer are consistent in all cases and show that protonated DMSA is a more potent methylating agent than protonated GB. Since methylation can occur at more than one site in arginine, the M+CH(3) ion of arginine, formed from the heterocluster DMSA+Arg+H, was subject to an additional stage of CID. The resultant CID spectrum is virtually identical to that of an authentic sample of protonated arginine-O-methyl ester but is significantly different to that of an authentic sample of protonated N(G)-methyl arginine. This suggests that methylation has occurred within a salt bridge complex of DMSA+Arg+H, in which the arginine exists in the zwitterionic form. Finally, density functional theory calculations on the model salts, (CH(3)CO(2)(-))[(CH(3))(3)S(+)] and (CH(3)CO(2)(-))[(CH(3))(4)N(+)], show that methylation of CH(3)CO(2)(-) by (CH(3))(3)S(+) is both kinetically and thermodynamically preferred over methylation by (CH(3))(4)N(+).
通过一系列气相实验，研究了已知的生物甲基化两性离子试剂——二甲基硫代乙酸盐（DMSA），(CH(3))(2)S⁺CH(2)CO(2)(-) （1）和甘氨酸甜菜碱（GB），(CH(3))(3)N⁺CH(2)CO(2)(-) （2）的固有甲基化能力，这些实验涉及它们的质子化同二聚体和异二聚体（包括含有氨基酸精氨酸的那些）的碰撞诱导解离（CID）。在所有情况下，甲基阳离子转移产物的相对产率都是一致的，并且表明质子化的DMSA是比质子化的GB更有效的甲基化剂。由于精氨酸中不止一个位点可以发生甲基化，由异簇DMSA+Arg+H形成的精氨酸的M+CH(3)离子经历了CID的额外阶段。所得的CID光谱与质子化精氨酸 - O - 甲酯的真实样品几乎相同，但与质子化N(G)-甲基精氨酸的真实样品有显著差异。这表明甲基化发生在DMSA+Arg+H的盐桥复合物中，其中精氨酸以两性离子形式存在。最后，对模型盐(CH(3)CO(2)(-))[(CH(3))(3)S(+)]和(CH(3)CO(2)(-))[(CH(3))(4)N(+)]的密度泛函理论计算表明，(CH(3))(3)S(+)对CH(3)CO(2)(-)的甲基化在动力学和热力学上都比(CH(3))(4)N(+)的甲基化更有利。
