Absolute quantitation of peptides and proteins has significance in biological analysis. Isotope labeled internal standards are routinely used for mass spectrometry (MS)-based absolute quantitation. However, syntheses of isotope-labeled peptides are time-consuming and costly. To tackle this issue, we recently developed a coulometric mass spectrometric (CMS) approach, based on the electrochemical oxidation of cysteine or tyrosine-containing peptides followed by mass spectrometric measurement of the oxidation yield. To demonstrate and further expand the utility of this method, herein, we present the CMS method for absolute quantitation of tryptophan-containing peptides. Several tryptophan-containing peptides, such as WGG, and WQPPRARI as well as one surrogate peptide GITWK from cytochrome c digest, were successfully quantified with a quantification error ranging from – 7.8 to + 4.3% based on the electrochemical oxidation of tryptophan. The validity of tryptophan-based absolute quantitation and no need for isotope-labeled peptide standards would definitely facilitate the further application of our CMS method in the absolute proteomic quantitation.

Absolute quantitation of tryptophan-containing peptides using coulometric mass spectrometry with no need to use standards

ACS Spring Meeting 2021

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