Liquid secondary-ion mass spectrometry of peptides containing multiple tyrosine-O-sulfates.
The behavior of peptides containing multiple tyrosine-O-sulfates in liquid secondary-ion mass spectrometry (LSIMS) has been investigated. In the positive-ion spectra of the peptides containing two tyrosine-O-sulfates, Cionin and CCK-associated C-terminal nonapeptide (CAP-9), the completely desulfated [M+H-2SO3]+ ions formed the base peaks, accompanying the significantly less-intense [M+H]+ and [M+H-SO3]+ ions. In the negative-ion spectra of these peptides, the [M-H]- and [M-H-SO3]- ions gave prominent peaks with significantly weaker [M-H-2SO3]- ions. In the case of a peptide containing three tyrosine-O-sulfates, [Tyr(SO3H).1]CAP-9, the completely desulfated [M+H-3SO3]+ ion again formed the base peak in the positive-ion spectrum. On the other hand, the sulfated tyrosine-containing [M+H]+, [M+H-SO3]+, and [M+H-2SO3]+ ions were of negligible abundance compared to the spectra of peptides containing two tyrosine-O-sulfates. We observed an intriguing 'ladder fragmentation pattern' in the negative-ion spectrum of this triply-sulfated peptide. The ladder consisted of the [M-H]-, [M-H-SO3]-, and [M-H-2SO3]- ions, but without the completely desulfated [M-H-3SO3]- ion. These characteristic fragmentation patterns of sulfated tyrosine-containing peptides were considered to bear a close correlation with the inherent acid-lability of a tyrosine-O-sulfate in solution. A possible mechanism has been proposed to explain the fragmentation patterns in the gaseous phase, in which a proton plays a decisive role.
National Institute of Health Sciences, Tokyo, Japan.
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Yagami
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Kitagawa
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Futaki
D000595:Amino Acid Sequence; D008969:Molecular Sequence Data; D010455:Peptides / Q000032:analysis*; D018629:Spectrometry, Mass, Secondary Ion; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry
D010455:Peptides; C005662:tyrosine O-sulfate; D014443:Tyrosine