The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Michael Fountoulakis - One of the best experts on this subject based on the ideXlab platform.
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quantification of cysteine residues following oxidation to Cysteic Acid in the presence of sodium azide
Analytical Biochemistry, 1995Co-Authors: Michael Manneberg, Hanswerner Lahm, Michael FountoulakisAbstract:Abstract Quantification of cysteines by amino Acid composition analysis is inaccurate because of decomposition of these residues during protein hydrolysis. Cysteine (and cystine) residues are oxidized to Cysteic Acid following hydrochloric Acid hydrolysis in the presence of sodium azide. Using selected native and recombinant proteins, containing different numbers of cysteine residues, we investigated the conditions for the quantitative oxidation of cysteines to Cysteic Acid in the presence of sodium azide. Protein hydrolysis with hydrochloric Acid in the presence of 0.20% sodium azide resulted in 87–100% oxidation of the cysteines to Cysteic Acid which was easily quantified. The results were highly reproducible so that the azide-induced oxidation can be used as a general method to determine cysteine residues in a given protein. The sodium azide-dependent oxidation is superior to oxidation with performic Acid because (i) it can be performed in solution not requiring protein lyophilization and in approximately half of the time; (ii) it delivers slightly higher yields of Cysteic Acid; and (iii) it does not affect tyrosine residues, which can be modified during the performic Acid treatment.
Simon J. Gaskell - One of the best experts on this subject based on the ideXlab platform.
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The promotion of d-type ions during the low energy collision-induced dissociation of some Cysteic Acid-containing peptides
Journal of the American Society for Mass Spectrometry, 1997Co-Authors: Scott G. Summerfield, Kathleen A. Cox, Simon J. GaskellAbstract:Low energy collisionally activated dissociations (CAD) of doubly protonated peptides incorporating Cysteic Acid and arginine residues have been studied. Deuterium labeling experiments have established that loss of the elements of H_2SO_3 occurs with cleavage of one CH bond and transfer of the hydrogen to a neutral fragment. Prominent d -type ions were observed corresponding to cleavage at the Cysteic Acid residue. The analysis of structural analogs suggested that the unexpectedly low energy requirement for this process is attributable to a charge-proximal process promoted by intra-ionic interaction of the arginine and Cysteic Acid side chains. CAD (in the collision hexapole of a tandem quadrupole instrument) of electrospray source-formed fragment ions established that the d -type ions can form via b -type ions; there was no evidence of formation via ( a _ n + 1) or ( b _ n — H_2SO_3) ions. The equivalent d -ion was observed, albeit with lesser abundance, when the Cysteic Acid residue was replaced by aspartic Acid, but not by glutamic Acid.
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Tandem mass spectrometric characterization of a specific Cysteic Acid residue in oxidized human apoprotein B-100
Journal of the American Society for Mass Spectrometry, 1995Co-Authors: Odile Burlet, Chaoyuh Yang, John R. Guyton, Simon J. GaskellAbstract:The oxidation of low density lipoprotein (LDL) in vivo may result in its unregulated uptake by macrophages, with the consequent accumulation of cholesterol that is characteristic of the development of atherosclerosis. This paper describes initial experiments to elucidate structural changes that occur in an in vitro model of LDL oxidation. LDL was isolated from human blood and oxidized in the presence of copper ion. Lipid was removed and the isolated apoprotein was subjected to tryptic hydrolysis. The hydrolysate was separated by high performance liquid chromatography and individual fractions were screened by amino Acid analysis to detect Cysteic Acid residues. Appropriate fractions were analyzed by fast atom bombardment mass spectrometry and hybrid tandem mass spectrometry. In this manner a tryptic fragment was identified that corresponded to residues 4187-4195 (EELCTMFIR), in which the cysteine and methionine residues were oxidized to Cysteic Acid and methionine sulfoxide, respectively. Identical analysis of LDL not subjected to in vitro oxidation revealed no evidence for this oxidized peptide. Earlier work established a surface location for this cysteine residue (Cys24) on the LDL particle, which suggested that its modification may significantly affect the properties of LDL, such as the propensity to intermolecular interaction via disulfide bridges. The analytical protocol developed here (involving proteolysis, screening of peptide fragments, and tandem mass spectrometry analysis) constitutes a strategy of general applicability to the characterization of targeted modifications of large proteins via mass spectrometry.
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influence of cysteine to Cysteic Acid oxidation on the collision activated decomposition of protonated peptides evidence for intraionic interactions
Journal of the American Society for Mass Spectrometry, 1992Co-Authors: Odile Burlet, Chaoyuh Yang, Simon J. GaskellAbstract:Oxidation of cysteine residues to Cysteic Acids in C-terminal arginine-eontaining peptides (such as those derived by tryptic digestion of proteins) strongly promotes the formation of multiple members of the Y− series of fragment ions following low energy collision-activated decomposition (CAD) of the protonated peptides, Removal of the arginine residue abolishes the effect, which is also attenuated by conversion of the arginine to dimethylpyrim-idylornithine. The data indicate the importance of an intraionic interaction between the Cysteic Acid and arginine side-chains. Low energy CAD of peptides which include Cysteic Acid and histidine residues, also provides evidence for intraionic interactions. It is proposed that these findings are consistent with the general hypothesis that an increased heterogeneity (with respect to location of charge) of the protonated peptide precursor ion population is beneficial to the generation of a high yield of product ions via several charge-directed, low energy fragmentation pathways. Furthermore, these data emphasize the significance of gas-phase conformations of protonated peptides in determining fragmentation pathways.
Michael Manneberg - One of the best experts on this subject based on the ideXlab platform.
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quantification of cysteine residues following oxidation to Cysteic Acid in the presence of sodium azide
Analytical Biochemistry, 1995Co-Authors: Michael Manneberg, Hanswerner Lahm, Michael FountoulakisAbstract:Abstract Quantification of cysteines by amino Acid composition analysis is inaccurate because of decomposition of these residues during protein hydrolysis. Cysteine (and cystine) residues are oxidized to Cysteic Acid following hydrochloric Acid hydrolysis in the presence of sodium azide. Using selected native and recombinant proteins, containing different numbers of cysteine residues, we investigated the conditions for the quantitative oxidation of cysteines to Cysteic Acid in the presence of sodium azide. Protein hydrolysis with hydrochloric Acid in the presence of 0.20% sodium azide resulted in 87–100% oxidation of the cysteines to Cysteic Acid which was easily quantified. The results were highly reproducible so that the azide-induced oxidation can be used as a general method to determine cysteine residues in a given protein. The sodium azide-dependent oxidation is superior to oxidation with performic Acid because (i) it can be performed in solution not requiring protein lyophilization and in approximately half of the time; (ii) it delivers slightly higher yields of Cysteic Acid; and (iii) it does not affect tyrosine residues, which can be modified during the performic Acid treatment.
Li Li - One of the best experts on this subject based on the ideXlab platform.
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simultaneous determination of ofloxacin and gatifloxacin on Cysteic Acid modified electrode in the presence of sodium dodecyl benzene sulfonate
Bioelectrochemistry, 2013Co-Authors: Fenfen Zhang, Shuqing Gu, Yaping Ding, Li LiAbstract:Abstract A novel Cysteic Acid modified carbon paste electrode (Cysteic Acid/CPE) based on electrochemical oxidation of l -cysteine was developed to simultaneously determine ofloxacin and gatifloxacin in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectra (FTIR) indicated that l -cysteine was oxidated to Cysteic Acid. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) indicated that Cysteic Acid was successfully modified on electrode. The large peak separation (116 mV) between ofloxacin and gatifloxacin was obtained on Cysteic Acid/CPE while only one oxidation peak was found on bare electrode. And the peak currents increased 5 times compared to bare electrode. Moreover, the current could be further enhanced in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate. The differential pulse voltammograms (DPV) exhibited that the oxidation peak currents were linearly proportional to their concentrations in the range of 0.06–10 μM for ofloxacin and 0.02–200 μM for gatifloxacin, and the detection limits of ofloxacin and gatifloxacin were 0.02 μM and 0.01 μM (S/N = 3), respectively. This proposed method was successfully applied to determine ofloxacin and gatifloxacin in pharmaceutical formulations and human serum samples.
Maryam Ramine - One of the best experts on this subject based on the ideXlab platform.
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electrocatalytic oxidation and voltammetric determination of l Cysteic Acid at the surface of p bromanil modified carbon paste electrode
Electroanalysis, 2006Co-Authors: Jahanbakhsh Raoof, Reza Ojani, Maryam RamineAbstract:The electrochemical properties of L-Cysteic Acid studied at the surface of p-bromanil (tetrabromo-p-benzoquinone) modified carbon paste electrode (BMCPE) in aqueous media by cyclic voltammetry (CV) and double step potential chronoamperometry. It has been found that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L-Cysteic Acid at the surface of BMCPE occurs at a half-wave potential of p-bromanil redox system (e.g., 100 mV vs. Ag|AgCl|KClsat), whereas, L-Cysteic Acid was electroinactive in the testing potential ranges at the surface of bare carbon paste electrode. The apparent diffusion coefficient of spiked p-bromanil in paraffin oil was also determined by using the Cottrell equation. The electrocatalytic oxidation peak current of L-Cysteic Acid exhibits a linear dependency to its concentration in the ranges of 8.00×10−6 M–6.00×10−3 M and 5.2×10−7 M–1.0×10−5 M using CV and differential pulse voltammetry (DPV) methods, respectively. The detection limits (2σ) were determined as 5.00×10−6 M and 4.00×10−7 M by CV and DPV methods. This method was used as a new, selective, rapid, simple, precise and suitable voltammetric method for determination of L-Cysteic Acid in serum of patient's blood with migraine disease.
