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Mass Shift (mass + shift)
Selected AbstractsInfluence on mass-selective ion ejection of the phase difference between the drive r.f. and the axial modulation potentialsJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2005G. Dobson Abstract The phase difference between the drive r.f. and the axial modulation potential is known to influence significantly the mass shift, and all commercial ion trap mass spectrometers use a fixed value for this difference. However, although this important parameter is partly responsible for the good precision achievable today in most commercial ion traps, little discussion on the variation of the phase difference between the drive r.f. and the axial modulation potential has appeared in the literature. We present here an examination of the influence of a low-level axial modulation potential superimposed by capacitive coupling between the electrodes. Low-level axial modulation potentials are used for certain analytical scans such as reverse scan or slow scan speeds. Such low-level potentials help to prevent deterioration of mass resolution due to, for example, the dissociation of the ions during their resonant ejection from the ion trap. Reverse and forward scans are used to illustrate the mass shift and change in resolution, caused by a change in the phase difference between the drive r.f. potential applied to the ring electrode and the axial modulation potential applied on an end-cap electrode, in electrospray ionization mass spectra. Copyright © 2005 John Wiley & Sons, Ltd. [source] A liquid chromatography/tandem mass spectrometry method for detecting UGT-mediated bioactivation of drugs as their N -acetylcysteine adducts in human liver microsomesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2009Hiroshi Harada The detection of the reactive metabolites of drugs has recently been gaining increasing importance. In vitro trapping studies using trapping agents such as glutathione are usually conducted for the detection of reactive metabolites, especially those of cytochrome P450-mediated metabolism. In order to detect the UDP-glucuronosyltransferase (UGT)-mediated bioactivation of drugs, an invitro trapping method using N -acetylcysteine (NAC) as a trapping agent followed by liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed in this study. After the test compounds (diclofenac and ketoprofen) had been incubated in human liver microsomes with uridine diphosphoglucuronic acid (UDPGA) and NAC, the NAC adducts formed through their acyl glucuronides were analyzed using LC/MS/MS with electrospray ionization (ESI). The NAC adduct showed a mass shift of 145 units as compared to its parent, and the characteristic ion fragmentations reflected the parent. This is a concise and high-throughput method for evaluating reactive metabolites by UGT-mediated bioactivation. Copyright © 2009 John Wiley & Sons, Ltd. [source] Characterization of bovine surfactant proteins B and C by electrospray ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2008Suya Liu Bovine surfactant proteins B (SP-B) and C (SP-C) were analyzed by nano-electrospray ionization mass spectrometry (nano-ESI-MS). The observed molecular masses showed discrepancies compared to the calculated molecular masses using the published amino acid sequences. The number of cysteine residues in the published bovine SP-B amino acid sequences also failed to match the observed mass shift upon reduction of the SP-B dimer. To determine the amino acid sequences of two proteins, SP-B was first digested with trypsin and analyzed by liquid chromatography/tandem mass spectrometry (LC/MS/MS), while SP-C was analyzed by MS/MS in its intact form. The amino acid sequence of bovine SP-B determined here matches the observed molecular mass. The sequence is almost identical to the sheep SP-B except for two amino acid residues, consistent with the proximity of the two species. The correct sequence contains seven cysteine residues. Bovine SP-B exists as dimers and all cysteines are oxidized to form disulfide bonds in physiological conditions, which is in agreement with the observed mass shift upon reduction of the SP-B dimer. These cysteine residues are completely conserved across all species indicating their importance for the biological functions of this surfactant protein. The sequence of SP-C determined here also reveals an L to V substitution at its position 22 compared with the published bovine SP-B sequence. Copyright © 2007 John Wiley & Sons, Ltd. [source] Screening for disulfide-rich peptides in biological sources by carboxyamidomethylation in combination with differential matrix-assisted laser desorption/ionization time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2001Susanne Neitz Peptides with biological functions often contain disulfide bridges connecting two cysteine residues. In an attempt to screen biological fluids for peptides containing cysteine residues, we have developed a sensitive and specific method to label cysteines selectively and detect the resulting molecular mass shift by differential mass spectrometry. First, reduction of disulfide bridges and carboxyamidomethylation of free thiols is adjusted to quantitatively achieve cysteine alkylation for complex peptide extracts. In a second step, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) before and after chemical derivatization is performed, followed by differential analysis to determine shifted peaks; shifted peaks belong to cysteine-containing peptides, other peaks remain unchanged. The number of cysteines can then be determined by the resulting molecular mass shift. Free, reduced cysteines are shifted by 57,u, two oxidized cysteines involved in disulfide bridges (cystine) result in a shift to higher mass per disulfide bridge of 116,u. Disulfide bridges connecting different amino acid chains like insulin break up during reduction. In this case, two peaks with lower molecular masses result from a single one in the unmodified sample. With this technique, we were able to identify cysteine-containing peptides and short fragments of proteins present in human blood filtrate. Copyright © 2001 John Wiley & Sons, Ltd. [source] Proteomic patterns for classification of ovarian cancer and CTCL serum samples utilizing peak pairs indicative of post-translational modificationsPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 22 2007Chenwei Liu Abstract Proteomic patterns as a potential diagnostic technology has been well established for several cancer conditions and other diseases. The use of machine learning techniques such as decision trees, neural networks, genetic algorithms, and other methods has been the basis for pattern determination. Cancer is known to involve signaling pathways that are regulated through PTM of proteins. These modifications are also detectable with high confidence using high-resolution MS. We generated data using a prOTOFÔ mass spectrometer on two sets of patient samples: ovarian cancer and cutaneous t-cell lymphoma (CTCL) with matched normal samples for each disease. Using the knowledge of mass shifts caused by common modifications, we built models using peak pairs and compared this to a conventional technique using individual peaks. The results for each disease showed that a small number of peak pairs gave classification equal to or better than the conventional technique that used multiple individual peaks. This simple peak picking technique could be used to guide identification of important peak pairs involved in the disease process. [source] Proteomics of ischemia/reperfusion injury in rabbit myocardium reveals alterations to proteins of essential functional systemsPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 5 2005Melanie Y. White Abstract Brief periods of myocardial ischemia prior to timely reperfusion result in prolonged, yet reversible, contractile dysfunction of the myocardium, or "myocardial stunning". It has been hypothesized that the delayed recovery of contractile function in stunned myocardium reflects damage to one or a few key sarcomeric proteins. However, damage to such proteins does not explain observed physiological alterations to myocardial oxygen consumption and ATP requirements observed following myocardial stunning, and therefore the impact of alterations to additional functional groups is unresolved. We utilized two-dimensional gel electrophoresis and mass spectrometry to identify changes to the protein profiles in whole cell, cytosolic- and myofilament-enriched subcellular fractions from isolated, perfused rabbit hearts following 15 min or 60 min low-flow (1 mL/min) ischemia. Comparative gel analysis revealed 53 protein spot differences (> 1.5-fold difference in visible abundance) in reperfused myocardium. The majority of changes were observed to proteins from four functional groups: (i) the sarcomere and cytoskeleton, notably myosin light chain-2 and troponin C; (ii) redox regulation, in particular several components of the NADH ubiquinone oxidoreductase complex; (iii) energy metabolism, encompassing creatine kinase; and (iv) the stress response. Protein differences appeared to be the result of isoelectric point shifts most probably resulting from chemical modifications, and molecular mass shifts resulting from proteolytic or physical fragmentation. This is consistent with our hypothesis that the time course for the onset of injury associated with myocardial stunning is too brief to be mediated by large changes to gene/protein expression, but rather that more subtle, rapid and potentially transient changes are occurring to the proteome. The physical manifestation of stunned myocardium is therefore the likely result of the summed functional impairment resulting from these multiple changes, rather than a result of damage to a single key protein. [source] Enhanced specificity of bacterial spore identification by oxidation and mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004Plamen A. DemirevArticle first published online: 18 OCT 200 Addition of an oxidizing agent (e.g., hydrogen peroxide) to intact spores selectively and completely oxidizes Met-containing biomarker proteins by formation of Met sulfoxides. This reaction increases the masses of the biomarker proteins observed in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of Bacillus spores by ,m,=,(16,×,n) Da, where n is the number of Met residues in the sequence of each individual protein. The procedure is very rapid, and can be performed in situ (i.e., on the MALDI target). It confirms the identity of individual biomarkers by comparing the number of Met amino acids from the experimentally determined mass shifts with predictions for n from the tentative amino acid sequence for each protein. In turn, accurate determination of n for several biomarkers allows rapid validation of the initial spore identification by MALDI-MS. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||