Fragmentations of [M - H](-) anions of peptides containing tyrosine sulfate. Does the sulfate group rearrange? A joint experimental and theoretical study

RationaleTo investigate the fragmentations in the negative-ion electrospray mass spectra of peptides containing tyrosine sulfate.MethodsPossible fragmentation mechanisms were explored using a Waters QTOF2 tandem mass spectrometer in concert with calculations at the CAM-B3LYP/6-311++g(d,p) level of theory.ResultsThe major negative ion formed in the ESI-MS of peptides containing tyrosine sulfate is [(M-H)-SO3](-) and this process normally yields the base peak of the spectrum. The basic backbone cleavages of [(M-H)-SO3](-) allowed the sequence of the peptide to be determined. Rearrangement reactions involving the formation of HOSO3(-) and [(M-H)-H2SO4](-) yielded minor peaks with relative abundances ≤ 10% and ≤ 2%, respectively.ConclusionsThe mass spectra of the [M-H](-) and [(M-H)-SO3](-) anions of peptides containing tyrosine sulfate allowed the position of the tyrosine sulfate group to be determined, together with the amino acid sequence of the peptide.T. T. Nha Tran, Tianfang Wang, Sandra Hack and John H. Bowi