Identification of Tyrosine and Nitrotyrosine with a Mixed-Mode Solid-Phase Extraction Cleanup Followed by Liquid Chromatography-Electrospray Time-of-Flight Mass Spectrometry in Plants.

In higher plants, there is a growing interest in the study of protein tyrosine nitration (NO2Tyr) as well as the identification of in vivo nitrated proteins. Different methods have been developed for identifying nitrotyrosine in biological samples. However, these analyses are difficult because tyrosine nitration is a very low-abundance posttranslational protein modification (PTM) and the lack of efficient enrichment methods for detection. The identification and quantification of NO2Tyr in proteins has represented a challenge for researchers.In this chapter a new method for determining NO2Tyr and tyrosine (Tyr) in Arabidopsis thaliana cell-suspension culture extracts is proposed. The quantification was performed using a simple, sensitive, and specific sample preparation assay based on mixed-mode solid-phase extraction (SPE) which was developed for the quantification of trace NO2Tyr in Arabidopsis extracts by liquid chromatography-electrospray time-of-flight mass spectrometry (LC-TOFMS).