Quantitation methods for peptides using mass spectrometry have advanced rapidly. These methods rely on using standard and/or isotope-labeled peptides, which might be difficult or expensive to synthesize. To tackle this challenge, we present a new approach for absolute quantitation without the use of standards or calibration curves based on coulometry combined with mass spectrometry (MS). In this approach, which we call coulometric mass spectrometry (CMS), the mass spectrum of a target peptide containing one or more tyrosine residues is recorded before and after undergoing electrochemical oxidation. We record the total integrated oxidation current from the electrochemical measurement, which according to the Faraday's Law of coulometry, provides the number of moles of oxidized peptide. The ion intensity ratio of the target peptide before and after oxidation provides an excellent estimate of the fraction of the peptide that has been oxidized, from which the total amount of peptide is calculated. The striking strength of CMS is that it needs no standard peptide, but CMS does require the peptide to contain a known number of oxidizable groups. To illustrate the power of this method, we analyzed various tyrosine-containing peptides such as GGYR, DRVY, oxytocin, [Arg8]-vasotocin and angiotensinogen 1-14 with a quantification error ranging from - 7.5 to + 2.4%. This approach is also applicable to quantifying phosphopeptides and could be useful in proteomics research.

中文翻译：

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通过库仑质谱法对可氧化肽进行绝对定量。

使用质谱的肽定量方法已迅速发展。这些方法依赖于使用标准和/或同位素标记的肽，这些肽可能难以合成或昂贵。为了解决这一挑战，我们提出了一种无需使用标准品或基于库仑法结合质谱（MS）的校准曲线即可进行绝对定量的新方法。在这种称为库仑质谱（CMS）的方法中，在进行电化学氧化之前和之后，记录包含一个或多个酪氨酸残基的目标肽的质谱。我们通过电化学测量记录总的总氧化电流，根据法拉第库仑法则，该电流提供了氧化肽的摩尔数。氧化前后靶肽的离子强度比可以很好地估算出被氧化肽的比例，从而可以计算出肽的总量。CMS的惊人优势在于它不需要标准肽，但是CMS确实需要该肽包含已知数量的可氧化基团。为了说明此方法的功效，我们分析了各种含酪氨酸的肽，例如GGYR，DRVY，催产素，[Arg8]-血管生成素和血管紧张素原1-14，定量误差范围为-7.5至+ 2.4％。这种方法也适用于定量磷酸肽，可能在蛋白质组学研究中很有用。CMS的惊人优势在于它不需要标准肽，但是CMS确实需要该肽包含已知数量的可氧化基团。为了说明此方法的功效，我们分析了各种含酪氨酸的肽，例如GGYR，DRVY，催产素，[Arg8]-血管生成素和血管紧张素原1-14，定量误差范围为-7.5至+ 2.4％。这种方法也适用于定量磷酸肽，可能在蛋白质组学研究中很有用。CMS的惊人优势在于它不需要标准肽，但是CMS确实需要该肽包含已知数量的可氧化基团。为了说明此方法的功效，我们分析了各种含酪氨酸的肽，例如GGYR，DRVY，催产素，[Arg8]-血管生成素和血管紧张素原1-14，定量误差范围为-7.5至+ 2.4％。这种方法也适用于定量磷酸肽，可能在蛋白质组学研究中很有用。