Sustained off-resonance irradiation for collision-activated dissociation involving Fourier transform mass spectrometry. Collision-activated dissociation technique that emulates infrared multiphoton dissociation

Secreted proteins of Mycobacterium tuberculosis are implicated in its disease pathogenesis and so are considered as potential diagnostic and vaccine candidates. The search for these has been slow, even though the entire genome sequence of M. tuberculosis is now available; of the 620 protein spots resolved by 2-D gel electrophoresis, 114 secreted proteins have been identified, but for only 13 has the primary structure been partly characterized. For comparison, in this top down mass spectrometry (MS) approach the secreted proteins were precipitated from cell culture filtrate, resuspended, and examined directly by electrospray ionization (ESI) Fourier transform MS. The ESI spectra of three precipitates showed 93, 535, and 369 molecular weight (M r ) values, for a total of 689 different values. However, only ϳ10% of these values matched (Ϯ1 Da) the DNA predicted M r values, but these identifications were unreliable. Of nine molecular ions characterized by MS/MS, only one protein match was confirmed, and its isotopic molecular ions were overlapped by those of another protein. MS/MS identified a total of ten proteins by sequence tag search, of which three were unidentified previously. The low success of M r matching was due to unusually extensive posttranslational modifications, including loss of a signal sequence, loss of the N-terminal residue, proteolytic degradation, oxidation, and glycosylation. Although in eubacteria the latter is relatively rare, a 9 kDa protein showed 7 hexose attachments and two 20 kDa proteins each had 20 attachments. For MS/MS, electron capture dissociation was especially effective. (J Am Soc Mass Spectrom 2003, 14, 253-261)

Section: Glycoprotein Preparationmentioning

confidence: 99%

Top down characterization of secreted proteins from Mycobacterium tuberculosis by electron capture dissociation mass spectrometry

ElNaggar

Sze

et al. 2003

“…Sustained off-resonance irradiation (SORI) [26] experiments were performed for the collision-induced dissociation (CID) studies. The off-resonance excitation was applied for 250 ms at 1000 Hz above the cyclotron resonance frequency for the ion of interest.…”

Section: Mass Spectrometrymentioning

confidence: 99%

Endgroup-assisted siloxane bond cleavage in the gas phase

Chen

2003

ϩ . The formation of SiC 5 H 16 NO ϩ involves dissociation of a Si™O bond and formation of an O™H bond through rearrangement. The fragmentation mechanism was investigated utilizing ab initio calculations and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry in combination with hydrogen/deuterium (H/D) exchange reactions. Sustained off-resonance irradiation collision-induced dissociation (SORI-CID) studies of the fully deuterated ion D 2 N(CH 2 ) 3 SiOSi(CH 2 ) 3 ND 3 ϩ provided convincing evidence for a backbiting mechanism which involves hydrogen transfer from the terminal amine group to the oxygen to form a silanol-containing species. Theoretical calculations indicated decomposition of H 2 N(CH 2 ) 3 SiOSi(CH 2 ) 3 NH 3 ϩ through a backbiting mechanism is the lowest energy decomposition channel, compared with other alternative routes. Two mechanisms were proposed for the fragmentation process which leads to the siloxane bond cleavage and the SORI-CID results of partially deuterated precursor ions suggest both mechanisms should be operative. Rearrangement to yield a silanol-containing product ion requires end groups possessing a labile hydrogen atom. Decomposition of disiloxane ions with end groups lacking labile hydrogen atoms yielded product ions from direct bond cleavages. (J

“…This is a very slow activation method with activation times approaching a fraction of a second and with low-energy-transfer to the reactant ions [12,13]. Sustained off-resonance irradiation (SORI) [15] in Fourier transform-ion cyclotron resonance instruments has similar characteristics. As a result of the long observation time and low excitation energy, there is ample time for rearrangement to occur before fragmentation.…”

mentioning

confidence: 99%

Fragmentation of protonated dipeptides containing arginine. Effect of activation method

Forbes

Jockusch

Young

et al. 2007

The fragmentation reactions of the protonated dipeptides Gly-Arg and Arg-Gly have been studied using collision-induced dissociation (CID) in a quadrupole ion trap, by in-source CID in a single-quadrupole mass spectrometer and by CID in the quadrupole cell of a QqTOF mass spectrometer. In agreement with earlier quadrupole ion trap studies (Farrugia, J. M.; O'Hair, R. A. J., Int. J. Mass Spectrom., 2003, 222, 229), the CID mass spectra obtained with the ion trap for the MH ϩ ions and major fragment ions are very similar for the two isomers indicating rearrangement to a common structure before fragmentation. In contrast, in-source CID of the MH ϩ ions and QqTOF CID of the MH ϩ , [MH Ϫ NH 3 ] ϩ and [MH Ͻ23 HN ϭ C(NH 2 ) 2 ] ϩ ions provide distinctly different spectra for the isomeric dipeptides, indicating that rearrangement to a common structure has not occurred to a significant extent under these conditions even near the threshold for fragmentation in the QqTOF instrument. Clearly, under normal operating conditions significantly different fragmentation behavior is observed in the ion trap and beam-type experiments. This different behavior probably can be attributed to the shorter observation times and concomitant higher excitation energies in the in-source and QqTOF experiments compared to the long observation times and lower excitation energies relevant to the ion trap experiments. Based largely on elemental compositions derived from accurate mass measurements in QqTOF studies fragmentation schemes are proposed for the MH ϩ , [MH Ϫ