Charge carrier field emission determines the number of charges on native state proteins in electrospray ionization
Charge carrier field emission determines the number of charges on native state proteins in electrospray ionization
复制标题
DOI：
10.1021/ja801280c
复制
发表时间：
2008-06-04
影响因子：
15
通讯作者：
Gross, Michael L.
中科院分区：
文献类型：
--
作者：
Hogan, Christopher J., Jr.;Carroll, James A.;Gross, Michael L.
尽管电喷雾电离(ESI)中的多次充电对于蛋白质质谱学是必不可少的，但多次充电的潜在机制还没有被阐明。在这里，我们提出了一个新的理论来描述自然状态蛋白质的ESI，并预测ESI中蛋白质上的额外电荷数。该理论认为，蛋白质在ESI中以带电残基的形式被电离，因为它们在溶剂挥发后保留了剩余的多余电荷，而不会从带电的ESI液滴中解吸。然而，它们的电荷状态并不是由与蛋白质大小相似的液滴的瑞利极限决定的；相反，它们的最终电荷状态是由电场诱导从含有蛋白质的ESI液滴发射带电的小溶质离子和团簇决定的。这一理论预测，在ESI中，蛋白质上的电荷数量应与气相蛋白质直径的平方成正比，并与发生离子从液滴中发射的临界电场强度E*成正比，该临界电场强度由液滴中过剩载流子(即溶质)的性质决定。分子量在5-76 kDa范围内的天然蛋白质在乙酸铵和三乙基碳酸氢铵中的电荷态测量与理论预测非常一致，并有力地支持了本文提出的蛋白质ESI的机理。
Although multiple charging in electrospray ionization (ESI) is essential to protein mass spectrometry, the underlying mechanism of multiple charging has not been explicated. Here, we present a new theory to describe ESI of native-state proteins and predict the number of excess charges on proteins in ESI. The theory proposes that proteins are ionized as charged residues in ESI, as they retain residual excess charges after solvent evaporation and do not desorb from charged ESI droplets. However, their charge state is not determined by the Rayleigh limit of a droplet of similar size to the protein; rather, their final charge state is determined by the electric field-induced emission of small charged solute ions and clusters from protein-containing ESI droplets. This theory predicts that the number of charges on a protein in ESI should be directly proportional to the square of the gas-phase protein diameter and to E*, the critical electric field strength at which ion emission from droplets occurs, This critical field strength is determined by the properties of the excess charge carriers (i.e., the solute) in droplets. Charge-state measurements of native-state proteins with molecular masses in the 5-76 kDa range in ammonium acetate and triethylammonium bicarbonate are in excellent agreement with theoretical predictions and strongly support the mechanism of protein ESI proposed here.