Chromatographic separation of tyrosine and meta-tyrosine

L-Tyrosine (Tyr) is one of the twenty proteinogenic amino acids. The direct oxidation of phenylalanine (precursor of Tyr) may lead to the formation of Tyr non-proteinogenic isomers, including meta-Tyr (m-Tyr), a marker of oxidative stress. Some plant species produce and accumulate high levels of m-tyrosine in their root tips via enzymatic pathways. Upon its release to soil, the Phe-analog, m-Tyr, affects early post-germination development (i.e., altered root development, cotyledon or leaf chlorosis, and retarded growth) of nearby plant life.  Due to this quality, m-Tyr can be used as an herbicide. In plants, the direct harmful effect of m-Tyr is due to its modification of the protein structure, whereas its indirect action is linked to the disruption of reactive oxygen and nitrogen species metabolism. In humans, the elevated concentration of m-Tyr is characteristic of various diseases and aging. In animal cells, m-Tyr is formed directly in response to oxidative stress, whereas, in plants, m-Tyr is also synthesized enzymatically and serves as a chemical weapon in plant–plant competition 

Instrumental: LC-MS/MS (Agilent 6410B, discontinued). The mass spectrometer was operated in positive ESI MRM mode. Chromatographic separation of meta, ortho, and para isomers using liquid chromatography is not a straightforward matter. For instance, Tyr and  m-Tyr could not be separated on all tested C-18 columns, Gemini hexyl-phenyl and Kinetex biphenyl columns and were successfully resolved only on the Kinetetex pentafluoro phenyl (PFP) column (2.1×150 mm, 2.6 µm particle size, Phenomenex).

Additionally, excellent separation of isomeric tyrosines was demonstrated using an ion-mobility SelexION device (Sciex, QTRAP 6500).