Direct identification of intramolecular disulfide links in peptides using negative ion electrospray mass spectra of underivatised peptides. A joint experimental and theoretical study

Date

2005

Authors

Bilusich, D.
Maselli, V.
Brinkworth, C.
Samguina, T.
Lebedev, A.
Bowie, J.

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Journal article

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Rapid Communications in Mass Spectrometry, 2005; 19(21):3063-3074

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Daniel Bilusich, Vita M. Maselli, Craig S. Brinkworth, Tatiana Samguina, Albert T. Lebedev, John H. Bowie

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Abstract

[M--H]- parent anions of underivatised peptides containing an intramolecular disulfide bridge undergo characteristic loss of the elements of H2S2, a process diagnostic of the presence of the disulfide moeity. This facile process is initiated from a side-chain enolate anion. Theoretical calculations (at the HF/6-31G(d)//AM1 level of theory) indicate that the process is exothermic with a small barrier. When the disulfide link involves a C-terminal Cys, the negative ion spectrum shows an [(M--H)--(H2S2+CO2)] fragment anion which is usually the main peak of the spectrum. This process is also directed by an enolate anion: theoretical calculations suggest a stepwise sequence with loss of CO2 preceding loss of H2S2. Both [(M--H)--H2S2] and [(M--H)--(H2S2+CO2)] anions undergo backbone cleavage allowing identification of the amino acid sequence of the peptide.

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Published Online: 3 Oct 2005

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The definitive version may be found at www.wiley.com

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