| Abstract
| - The wide range of protein concentrations found in biological matrixes presents a formidable analytical challenge inproteomics experiments. It is predicted that low-abundance proteins are the likely clinically relevant targets indisease-based proteomics analyses. To effectively analyzelow-abundance proteins by electrospray ionization massspectrometry, limits of detection must be improved upon.Previous studies have demonstrated hydrophobicity is amain determinant of the electrospray ionization response.One would expect to improve the electrospray ionizationresponse of a hydrophilic peptide by making it morehydrophobic, thus increasing the molecule's affinity forthe surface of the electrospray droplet, thereby allowingthe molecule to more effectively compete for charge. Inthis report, we demonstrate a strategy to increase theelectrospray ionization response of cysteine-containingpeptides with the addition of an octylcarboxyamidomethylmodification via alkylation chemistry, which we name theALiPHAT strategy (augmented limits of detection forpeptides with hydrophobic alkyl tags). We demonstratethe relative increase in electrospray ionization responseof peptides with an octylcarboxyamidomethyl modificationcompared to carboxyamidomethyl-modified peptides uponLC−MS analysis. Furthermore, we show the octylcarboxyamidomethyl group does not fragment or undergoneutral loss during collision-induced dissociation. Collectively, our results demonstrate the feasibility of theoctylcarboxyamidomethyl modification to improve limitsof detection for cysteine-containing peptides.
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