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

Abstract

<h4>Rationale</h4>To investigate the fragmentations in the negative-ion electrospray mass spectra of peptides containing tyrosine sulfate.<h4>Methods</h4>Possible 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.<h4>Results</h4>The 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.<h4>Conclusions</h4>The 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.