on 06-19-201409:17 AM - edited on 10-15-202111:37 AM by AnalyteGuru
Lebedev AT, Damoc E, Makarov A, Samgina TY. Anal Chem. 2014 Jun 18. An efficient approach to easy and reliable differentiation between isomeric leucine and isoleucine in peptide sequencing utilizes multi-stage electron transfer dissociation and higher energy collision activated dissociation in the Orbitrap Fusion mass spectrometer. The MS3 method involves production and isolation of primary odd-electron z. ions, followed by radi-cal site initiation of their fragmentation with formation of w-ions, characteristic of the isomeric amino acid residues. Six natural non-tryptic peptides isolated from the secretion of frog Rana ridibunda were studied. Their lengths were in the range between 15 and 37 amino acids and the number of targeted isomeric (Leu/Ile) residues varied between 1 and 7. The experiments were successful in all 22 cases of Leu/Ile residues, leaving no doubts in identification. The method is extremely selective as the targeted w-ions appear to be the most intense in the spectra. The proposed approach may be incorporated into shotgun proteomics algorithms and allows for the development of an exclusively mass spectrometric method for automated complete de novo sequencing of various peptides and proteins.