We present mechanistic studies aimed at improving the understanding of the product ion formation rules in electron capture dissociation (ECD) of peptides and proteins in Fourier transform ion cyclotron resonance mass spectrometry. In particular, we attempted to quantify the recently reported general correlation of ECD product ion abundance (PIA) with amino acid hydrophobicity. The results obtained on a series of model H-RAAAAXAAAAK-OH peptides confirm a direct correlation of ECD PIA with X amino acid hydrophobicity and polarity. The correlation factor (R) exceeds 0.9 for 12 amino acids (Ile, Val, His, Asn, Asp, Glu, Gln, Ser, Thr, Gly, Cys, and Ala). The deviation of ECD PIA for seven outliers (Pro is not taken into consideration) is explained by their specific radical stabilization properties (Phe, Trp, Tyr, Met, and Leu) and amino acid basicity (Lys, Arg). Phosphorylation of Ser, Thr, and Tyr decreases the efficiency of ECD around phosphorylated residues, as expected. The systematic arrangement of amino acids reported here indicates a possible route toward development of a predictive model for quantitative electron capture/transfer dissociation tandem mass spectrometry, with possible applications in proteomics.

我们提出的机理研究旨在提高对傅立叶变换离子回旋共振质谱中肽和蛋白质电子捕获解离 (ECD) 中产物离子形成规则的理解。特别是，我们试图量化最近报道的 ECD 产物离子丰度 (PIA) 与氨基酸疏水性的一般相关性。在一系列模型 H-RAAAAXAAAAK-OH 肽上获得的结果证实了 ECD PIA 与 X 氨基酸疏水性和极性的直接相关性。12 个氨基酸（Ile、Val、His、Asn、Asp、Glu、Gln、Ser、Thr、Gly、Cys 和 Ala）的相关因子 (R) 超过 0.9。七个异常值（不考虑 Pro）的 ECD PIA 偏差由它们特定的自由基稳定特性（Phe、Trp、Tyr、Met、和 Leu) 和氨基酸碱度 (Lys, Arg)。正如预期的那样，Ser、Thr 和 Tyr 的磷酸化会降低磷酸化残基周围的 ECD 效率。此处报告的氨基酸的系统排列表明了开发定量电子捕获/转移解离串联质谱预测模型的可能途径，并可能在蛋白质组学中应用。