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1.
T. Yu. Samgina V. A. Gorshkov Ye. A. Vorontsov E. V. Demkina S. V. Ogourtsov V. V. Shakhparonov G. I. El-Registan A. T. Lebedev 《Journal of Analytical Chemistry》2011,66(14):1361-1368
Skin secretory amphibian antimicrobial peptides are the part of their immune defense. The present work is devoted to the study
of the influence of “water environment stress” and additional bacterial impact on the composition of the skin secretion of
the Common frog (Rana temporaria) by means of high-performance liquid chromatography (HPLC) and matrix assisted laser desorption/ionization (MALDI) mass spectrometry.
It was shown that the contact of the amphibian species with Micrococcus luteus and Staphylococcus aureus stimulates the release of antimicrobial peptides, maintains the high bradykinin and related peptides levels in the skin secretion
and influences the processing of the latter ones. The possibilities of mass spectrometric profiling by using HPLC and MALDI
were demonstrated. This feature allows the detection of potentially bioactive peptides for their future direct testing, as
has been shown for temporin M and brevinin 1Tb in the present study. 相似文献
2.
《Journal of mass spectrometry : JMS》2017,52(2):127-131
The ability of a thiol‐containing molecule, thiosalicylic acid (TSA), to function as a reactive matrix for matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry analysis of peptides has been investigated. Although TSA has reducing characteristics, the use of TSA did not cause a reduction‐induced MALDI in‐source decay, probably because of the weak interactions between the thiol group in TSA and the carboxyl oxygen in the peptide. In contrast, when peptides containing disulfide bonds were analyzed by MALDI with TSA as the matrix, the disulfide bond was partially cleaved owing to the reaction with TSA, producing TSA‐adducted peptides. The reaction between the disulfide bond and TSA was suggested to be occurred in solution. The comparison of the MALDI mass spectra obtained using conventional matrix and TSA allows us to count the number of disulfide bonds in the peptides. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
3.
T. Yu. Samgina V. A. Gorshkov Ye. A. Vorontsov K. A. Artemenko S. V. Ogourtsov R. A. Zubarev A. T. Lebedev 《Journal of Analytical Chemistry》2011,66(14):1353-1360
Skin secretions of amphibian are an interesting source of biologically active peptides. The present study provides the profile
of the skin secretions of the brown frog Rana temporaria from Zvenigorod population (Russia). Sequencing of the skin secretion components has been carried out on an ion cyclotron
resonance instrument with electrospray ionization and two methods of fragmentation activation, collisional activation and
electron capture. For sequencing of the peptides containing intermolecular C-terminal disulfide cycle two methods of disulfide
bond opening have been used: reduction with subsequent alkylation of the free thiol groups and oxidation with performic acid
with the formation of sulfo-acid groups. The peptide profile of Rana temporaria studied by a complex mass spectral method has been compared with the data for the frogs of other European populations of
this species. For the first time we have revealed ornithokinin-antagonist of the ornithokinin receptor-in skin secretions
of amphibians. 相似文献
4.
T. Yu. Samgina V. A. Gorshkov Ye. A. Vorontsov K. A. Artemenko S. V. Ogourtsov R. A. Zubarev A. T. Lebedev 《Journal of Analytical Chemistry》2011,66(13):1298-1306
Amphibian skin secretion represents a cerain scientific interest as a source of biologically active natural peptides. In the
present research skin peptidome of wide-spread European frog Rana lessonae (Camerano, 1882) was studied for the first time ever. Peptide sequencing was accomplished with Fourier transform ion cyclotron
resonance mass spectrometer in collision-induced and electron capture dissociation modes. A portion of amphibian peptides
contains intramolecular C-terminal disulfide cycle which obstructs mass spectrometric sequencing. Two methods were utilized
to overcome this difficulty: reduction with dithiotreithol followed by thiol group alkylation and oxidation into sulfonic
acid groups with performic acid. Integrated approach employed in the present study allowed the identification of 49 peptides
(of 6 to 37 amino acid residues), including 19 novel species. 相似文献
5.
Hongmei Yang Ning Liu Xiaoyan Qiu Shuying Liu 《Journal of the American Society for Mass Spectrometry》2009,20(12):2284-2293
A simple and high-throughput method for the identification of disulfide-containing peptides utilizing peptide-matrix adducts
is described. Some commonly used matrices in MALDI mass spectrometry were found to specifically react with sulfhydryl groups
within peptide, thus allowing the observation of the peptide-matrix adduct ion [M+n+n′ matrix+H]+ or [M+n+n′ matrix+Na]+ (n = the number of cysteine residues, n′=1, 2,…, n) in MALDI mass spectra after chemical reduction of disulfide-linked peptides. Among several matrices tested, α-cyano-4-hydroxycinnamic
acid (CHCA, molecular mass 189 Da) and α-cyano-3-hydroxycinnamic acid (3-HCCA) were found to be more effective for MALDI analysis
of disulfide-containing peptides/proteins. Two reduced cysteines involved in a disulfide bridge resulted in a mass shift of
189 Da per cysteine, so the number of disulfide bonds could then be determined, while for the other matrices (sinapinic acid,
ferulic acid, and caffeic acid), a similar addition reaction could not occur unless the reaction was carried out under alkaline
conditions. The underlying mechanism of the reaction of the matrix addition at sulfhydryl groups is proposed, and several
factors that might affect the formation of the peptide-matrix adducts were investigated. In general, this method is fast,
effective, and robust to identify disulfide bonds in proteins/peptides. 相似文献
6.
Jong-Seo Kim Enshi Cui Hie-Joon Kim 《Journal of the American Society for Mass Spectrometry》2009,20(9):1751-1758
Two orders of magnitude matrix-assisted laser desorption/ionization (MALDI) signal enhancement of phosphopeptides has been
achieved by picolinamidination of N-terminal amine group and ε-amine group of lysine residues. Due to the presence of picolinamidination tag at the N-terminal amine of peptides, MS/MS
spectra with a strong b-ion series was obtained, which greatly facilitated sequencing and identification of the phosphorylation
site. Phosphorylation site of a phosphopeptide could be identified from MALDI TOF/TOF spectrum obtained from a tryptic or
a chymotryptic phosphopeptide, which was not even detected in the positive ion mode, without signal enhancement by picolinamidination,
due to the negative charge of the phosphate group in the presence of other peptides. 相似文献
7.
Eric B. Monroe Beth Anne Koszczuk Jenna L. Losh John C. Jurchen Jonathan V. Sweedler 《International journal of mass spectrometry》2007,260(2-3):237
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) has been used for the discovery of hundreds of novel cell to cell signaling peptides. Beyond its advantages of sensitivity and minimal sample preparation requirements, MALDI MS is attractive for biological analyses as high quality mass spectra may be obtained directly from specific locations within prepared tissue sections. However, due to the large quantity of salts present in physiological tissues, these mass spectra often contain many adducts of cationic salts such as sodium and potassium, in addition to the molecular ion [M + H]+. To reduce the presence of cation adducts in MALDI mass spectra obtained directly from tissues, we present a methodology that uses a slow condensation procedure to enable the formation of distinct regions of matrix/analyte crystals and cation (salt) crystals. Secondary ion mass spectrometric imaging suggests that the salts and MALDI matrix undergo a mutually exclusive crystallization process that results in the separation of the salts and matrix in the sample. 相似文献
8.
Membrane protein and peptide sample handling for MS analysis using a structured MALDI target 总被引:1,自引:0,他引:1
Different sample handling methods for hydrophobic proteins and peptides were evaluated in association with the utilization of a structured matrix-assisted laser/desorption ionization (MALDI) target for increased sensitivity. The fluorinated organic solvent hexafluoroisopropanol (HFIP) was used for the solubilization of both the full-length protein bacteriorhodopsin (BR) and a cyanogen bromide digest thereof, and compared to the performance of the non-ionic detergents octyl--d-glucopyranoside (OG), dodecyl--d-maltoside (DM), and Triton X-100. A concentrating effect was seen when using the structured MALDI plate for BR dissolved in all the different detergents, of which OG generated the best-quality spectra for the full-length integral membrane protein as well as for the hydrophobic peptides. However, the uneven analyte distribution obtained with the detergent preparations required selective and thus time-consuming acquisition of spectra. When instead HFIP was used as sample solvent, a tenfold increase in sensitivity was achieved for full-length BR. Addition of acids to the HFIP-solubilized sample, or to the MALDI matrix solution, improved the signals for a few of the peptides, while degrading the spectra of others. Consequently, the addition of acid could be used as a complementary sample preparation method for hydrophobic peptides. On-target washing to remove contaminants (e.g., salt) was performed, and a recrystallization protocol for signal improvement specifically suited for hydrophobic peptides is described. Results from digestion and solubilization in different micro centrifuge tubes were examined to determine the influence of different materials on the possible sample loss due to wall adhesion. Studies of sample solution storage times suggest immediate analysis after solubilization to obtain best results. 相似文献
9.
T. Yu. Samgina K. A. Artemenko V. A. Gorshkov S. V. Ogourtsov R. A. Zubarev A. T. Lebedev 《Rapid communications in mass spectrometry : RCM》2009,23(9):1241-1248
A high‐performance liquid chromatography nano‐electrospray ionization Fourier transform mass spectrometry (HPLC/nanoESI‐FTMS) approach involving recording of collision‐activated dissociation (CAD) and electron‐capture dissociation (ECD) spectra of an intact sample and two its modifications after performic oxidation and reduction followed by carboxamidomethylation helps to establish peptide profiles in the crude secretion of frog species at mid‐throughput level, including de novo sequencing. The proposed derivatization procedures allow increasing of the general sequence coverage in the backbone, providing complementary information and, what is more important, reveal the amino acid sequence in the cystine ring (‘rana box’). Thus purely mass spectrometric efficient sequencing becomes possible for longer than usual proteolytic peptides. Seventeen peptides belonging to four known families were identified in the secretion of the European brown frog Rana arvalis inhabiting the Moscow region in Russia. Ranatuerins, considered previously a unique feature of the North American species, as well as a new melittin‐related peptide, are worth special mention. The developed approach was previously successfully used for the identification of peptides in the skin secretion of the Caucasian green frog Rana ridibunda. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
10.
Bernd Enthaler Maria Trusch Markus Fischer Claudius Rapp Julia K. Pruns Jens-Peter Vietzke 《Analytical and bioanalytical chemistry》2013,405(4):1159-1170
Matrix-assisted laser/desorption ionization (MALDI) mass-spectrometric imaging (MSI), also known as MALDI imaging, is a powerful technique for mapping biological molecules such as endogenous proteins and peptides in human skin tissue sections. A few groups have endeavored to apply MALDI-MSI to the field of skin research; however, a comprehensive article dealing with skin tissue sections and the application of various matrices and enzymes is not available. Our aim is to present a multiplex method, based on MALDI-MSI, to obtain the maximum information from skin tissue sections. Various matrices were applied to skin tissue sections: (1) 9-aminoacridine for imaging metabolites in negative ion mode; (2) sinapinic acid to obtain protein distributions; (3) α-cyano-4-hydroxycinnamic acid subsequent to on-tissue enzymatic digestion by trypsin, elastase, and pepsin, respectively, to localize the resulting peptides. Notably, substantial amounts of data were generated from the distributions retrieved for all matrices applied. Several primary metabolites, e.g. ATP, were localized and subsequently identified by on-tissue postsource decay measurements. Furthermore, maps of proteins and peptides derived from on-tissue digests were generated. Identification of peptides was achieved by elution with different solvents, mixing with α-cyano-4-hydroxycinnamic acid, and subsequent tandem mass spectrometry (MS/MS) measurements, thereby avoiding on-tissue MS/MS measurements. Highly abundant peptides were identified, allowing their use as internal calibrants in future MALDI-MSI analyses of human skin tissue sections. Elastin as an endogenous skin protein was identified only by use of elastase, showing the high potential of alternative enzymes. The results show the versatility of MALDI-MSI in the field of skin research. This article containing a methodological perspective depicts the basics for a comprehensive comparison of various skin states. Figure
Matrix-assisted laser/desorption ionization (MALDI) mass-spectrometric imaging (MSI), also known as MALDI imaging, is a powerful technique for mapping biological molecules in human skin tissue sections. In this body of work, a multiplex method, based on MALDI-MSI, is presented to obtain maximum information from skin tissue sections. Therefore, various matrices were applied to skin tissue sections: (1) 9-aminoacridine (9-AA) for imaging small molecules in negative ion mode; (2) sinapinic acid (SA) to obtain protein distributions; (3) α-cyano-4-hydroxycinnamic acid (α-HCHA) subsequent to on-tissue enzymatic digestion by trypsin, elastase, and pepsin, respectively, to localize the resulting peptides. Of note, identification of metabolites was achieved by post-source decay (PSD) MALDI, and proteins were identified subsequent to enzymatic digestion via the resulting peptides which were eluted from the skin tissue section and afterwards analyzed with use of a tandem time-of-flight (ToF) mass spectrometer. The application of alternative enzymes, such as pepsin and elastase, is highlighted within this article 相似文献
11.
In this work, partial characterization of the primary structure of phycocyanin from the cyanobacterium Aphanizomenon flos‐aquae (AFA) was achieved by mass spectrometry de novo sequencing with the aid of chemical derivatization. Combining N‐terminal sulfonation of tryptic peptides by 4‐sulfophenyl isothiocyanate (SPITC) and MALDI‐TOF/TOF analyses, facilitated the acquisition of sequence information for AFA phycocyanin subunits. In fact, SPITC‐derivatized peptides underwent facile fragmentation, predominantly resulting in y‐series ions in the MS/MS spectra and often exhibiting uninterrupted sequences of 20 or more amino acid residues. This strategy allowed us to carry out peptide fragment fingerprinting and de novo sequencing of several peptides belonging to both α‐ and β‐phycocyanin polypeptides, obtaining a sequence coverage of 67% and 75%, respectively. The presence of different isoforms of phycocyanin subunits was also revealed; subsequently Intact Mass Measurements (IMMs) by both MALDI‐ and ESI‐MS supported the detection of these protein isoforms. Finally, we discuss the evolutionary importance of phycocyanin isoforms in cyanobacteria, suggesting the possible use of the phycocyanin operon for a correct taxonomic identity of this species. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
Sung Hee Ahn Kyung Man Park Yong Jin Bae Myung Soo Kim 《Journal of mass spectrometry : JMS》2013,48(3):299-305
In a previous study on matrix‐assisted laser desorption ionization (MALDI) of peptides using α‐cyano‐4‐hydroxycinnamic acid (CHCA) as a matrix, we found that the patterns of single‐shot spectra obtained under different experimental conditions became similar upon temperature selection. In this paper, we report that absolute ion abundances are also similar in temperature‐selected MALDI spectra, even when laser fluence is varied. The result that has been obtained using CHCA and 2,5‐dihydroxybenzoic acid as matrices is in disagreement with the hypothesis of laser‐induced ionization of matrix as the mechanism for primary ion formation in MALDI. We also report that the total number of ions in such a spectrum is unaffected by the identity, concentration and number of analytes, i.e. it is the same as that in the spectrum of pure matrix. We propose that the generation of gas‐phase ions in MALDI can be explained in terms of two thermal reactions, i.e. the autoprotolysis of matrix molecules and the matrix‐to‐analyte proton transfer, both of which are in quasi‐equilibrium in the early matrix plume. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
13.
Joachim D. Uys Angus C. Grey Armina Wiggins John H. Schwacke Kevin L. Schey Peter W. Kalivas 《Journal of mass spectrometry : JMS》2010,45(1):97-103
Proteins in the nucleus accumbens mediate many cocaine‐induced behaviors. In an effort to measure changes in nucleus accumbens protein expression as potential biomarkers for addiction, coronal tissue sections were obtained from rats that developed behavioral sensitization after daily administration of cocaine, or from daily saline‐treated controls. The tissue sections were subjected to matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry (MS) profiling and tissue imaging. For profiling experiments, brain sections were manually spotted with matrix over the nucleus accumbens, a brain region known to regulate cocaine sensitization. Summed mass spectra (10 000 laser shots, grid) were acquired and spectra were aligned to reference peaks. Using bioinformatics tools, eight spectral features were found to be altered by cocaine treatment. Based on additional sequencing experiments with MALDI tandem MS and database searches of measured masses, secretoneurin (m/z 3653) was identified as having an increased expression. In addition, the distribution of m/z 3653 in the nucleus accumbens was determined by MALDI tissue imaging, and the increased expression of its precursor protein, secretogranin II, was verified by immunoblotting. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
14.
Matrix‐assisted laser desorption/ionization in‐source decay (MALDI‐ISD) has been used for characterization of a phosphorylated peptides and proteins because labile phosphate group is not lost during the MALDI‐ISD process. The conventional MALDI‐ISD is initiated by the hydrogen transfer from reducing matrix molecules to peptide backbone, leading to c′‐ and z′‐series ions. In contrast, when an oxidizing chemical 5‐nitrosalicylic acid (5‐NSA) is served as the MALDI‐ISD matrix, a‐ and x‐series ions are specifically generated by hydrogen abstraction from peptide backbone to matrix molecule. The 5‐NSA provides useful complementary information to the conventional MALDI‐ISD for the analysis of amino acid sequencing and site localization of phosphorylation in peptides. The MALDI‐ISD with reducing and oxidizing matrix could be a useful method for the de novo peptide sequencing. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
15.
Donatella Chionna Concetto Puglisi Filippo Samperi Giorgio Montaudo Antonio Turturro 《Macromolecular rapid communications》2001,22(7):524-529
Matrix‐assisted laser desorption ionisation (MALDI) mass spectrometry was used, in an attempt to find firm evidence for the structure of the species produced in the thermal oxidative degradation of Nylon 6 (Ny6), at 250°C in air. The MALDI spectra of the products showed the presence of polymer chains containing aldehydes, amides, methyl and N‐formamide terminal groups. The aldehydes undergo further oxidation to produce carboxylic end groups. The formation of azomethines, from the further reaction of aldehydes with amino‐terminated Ny6 chains, is also supported by the appearance of specific peaks in the MALDI spectra. 相似文献
16.
Markus Langsdorf Alireza Ghassempour Andreas Römpp Bernhard Spengler 《Analytical and bioanalytical chemistry》2010,398(7-8):2853-2865
Novel peptides were identified in the skin secretion of the tree frog Hyla savignyi. Skin secretions were collected by mild electrical stimulation. Peptides were separated by reversed-phase high-performance liquid chromatography. Mass spectra were acquired by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), and fragment ion spectra were obtained after collision-induced dissociation and electron capture dissociation. Peptides were analyzed by manual de novo sequencing and composition-based sequencing (CBS). Sequence analyses of three so far undescribed, structurally unrelated peptides are presented in this paper, having the sequences DDSEEEEVE-OH, P*EEVEEERJK-OH, and GJJDPJTGJVGGJJ-NH2. The glutamate-rich sequences are assumed to be acidic spacer peptides of the prepropeptide. One of these peptides contains the modified amino acid hydroxyproline, as identified and localized by high-accuracy FTICR-MS. Combination of CBS and of experience-based manual sequence analysis as complementary and database-independent sequencing strategies resulted in peptide identification with high reliability. Figure
So-far unknown natural frog skin peptides were identified by high-resolution CID and ECD MS/MS and by composition-based de novo sequencing. Sequences were confirmed by comparison of MS/MS spectra with synthesized analogs 相似文献
17.
Raymond E. West III Eric W. Findsen Dragan Isailovic 《Journal of the American Society for Mass Spectrometry》2013,24(10):1467-1476
We report the development of a new AP visible-wavelength MALDI-ion trap-MS instrument with significantly improved performance over our previously reported system (Int. J. Mass Spectrom. 315, 66–73 (2012)). A Nd:YAG pulsed laser emitting light at 532 nm was used to desorb and ionize oligosaccharides and peptides in transmission geometry through a glass slide. Limits of detection (LODs) achieved in MS mode correspond to picomole quantities of oligosaccharides and femtomole quantities of peptides. Tandem MS (MS/MS) experiments enabled identification of enzymatically digested proteins and oligosaccharides by comparison of MS/MS spectra with data found in protein and glycan databases. Moreover, the softness of ionization, LODs, and fragmentation spectra of biomolecules by AP visible-wavelength MALDI-MS were compared to those obtained by AP UV MALDI-MS using a Nd:YAG laser emitting light at 355 nm. AP visible-wavelength MALDI appears to be a softer ionization technique then AP UV MALDI for the analysis of sulfated peptides, while visible-wavelength MALDI-MS, MS/MS, and MS/MS/MS spectra of other biomolecules analyzed were mostly similar to those obtained by AP UV MALDI-MS. Therefore, the methodology presented will be useful for MS and MSn analyses of biomolecules at atmospheric pressure. Additionally, the AP visible-wavelength MALDI developed can be readily used for soft ionization of analytes on various mass spectrometers. Figure
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18.
Farid Jahouh Rina Saksena Donatella Aiello Anna Napoli Giovanni Sindona Pavol Kováč Joseph H. Banoub 《Journal of mass spectrometry : JMS》2010,45(10):1148-1159
We present the MALDI‐TOF/TOF‐MS analyses of various hapten–bovine serum albumin (BSA) neoglycoconjugates obtained by squaric acid chemistry coupling of the spacer‐equipped, terminal monosaccharide of the O‐specific polysaccharide of Vibrio cholerae O1, serotype Ogawa, to BSA. These analyses allowed not only to calculate the molecular masses of the hapten–BSA neoglycoconjugates with different hapten–BSA ratios (4.3, 6.6 and 13.2) but, more importantly, also to localize the covalent linkages (conjugation sites) between the hapten and the carrier protein. Determination of the site of glycation was based on comparison of the MALDI‐TOF/TOF‐MS analysis of the peptides resulting from the digestion of BSA with similar data resulting from the digestion of BSA glycoconjugates, followed by sequencing by MALDI‐TOF/TOF‐MS/MS of the glycated peptides. The product‐ion scans of the protonated molecules were carried out with a MALDI‐TOF/TOF‐MS/MS tandem mass spectrometer equipped with a high‐collision energy cell. The high‐energy collision‐induced dissociation (CID) spectra afforded product ions formed by fragmentation of the carbohydrate hapten and amino acid sequences conjugated with fragments of the carbohydrate hapten. We were able to identify three conjugation sites on lysine residues (Lys235, Lys437 and Lys455). It was shown that these lysine residues are very reactive and bind lysine specific reagents. We presume that these Lys residues belong to those that are considered to be sterically more accessible on the surface of the tridimensional structure. The identification of the y‐series product ions was very useful for the sequencing of various peptides. The series of a‐ and b‐product ions confirmed the sequence of the conjugated peptides. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
19.
Dong Cao Yangjun Zhang Huihui Zhang Liangwei Zhong Xiaohong Qian 《Rapid communications in mass spectrometry : RCM》2009,23(8):1147-1157
(?)‐Epigallocatechin gallate (EGCG) is a major bioactive component in leaves of green tea, and has been widely investigated for its anti‐tumor activity. The interaction between EGCG and the key peptides or proteins (e.g. glutathione, enzymes) in vivo is thought to be involved in the toxicity and anti‐cancer mechanism of EGCG. However, the true anti‐tumor mechanism of EGCG is not clear, and few studies have focused on the reactivity of EGCG toward peptides or proteins under physiological conditions (pH 7.4, 37°C). In this work, the covalent interactions between EGCG and model peptides containing one or more nucleophilic residues (i.e. Arg, Cys, Met, and α‐NH2 of the N‐terminus of peptides) under physiological condition were fully characterized using mass spectrometry. It was found that EGCG can react with the thiol groups of peptides to form adducts under physiological conditions (pH 7.4, 37°C), even in the absence of the peroxidase/hydrogen peroxide system. Besides the thiol groups of peptides, it is firstly reported that EGCG also reacts with α‐NH2 of the N‐terminus or arginine residues of model peptides to form Schiff base adducts, and the methionine residues of model peptides can be easily oxidized by hydrogen peroxide (H2O2) generated during the process of EGCG auto‐oxidation to form methionine sulfoxide products. The preference for the reaction of nucleophlic residues of peptides with EGCG was determined to have the following order: Cys > α‐NH2 of the N‐terminus > Arg. The neutral loss ions of [M+H–170]+ and [M+H‐138]+ were detected in all tandem mass spectra of the EGCG adducts of peptides, which indicates that these two neutral loss ions can be considered as the characteristic neutral loss ions of peptides modified by EGCG. Results of the present research provide insights into the toxicology and anti‐tumor mechanism of EGCG in vivo. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
20.
Christopher Barner‐Kowollik Philipp Vana Thomas P. Davis 《Journal of polymer science. Part A, Polymer chemistry》2002,40(5):675-681
Pulsed laser polymerization (PLP) experiments were performed on the bulk polymerization of methyl methacrylate (MMA) at ?34 °C. The aim of this study was to investigate the polymer end groups formed during the photoinitiation process of MMA monomer using 2,2‐dimethoxy‐2‐phenylacetophenone (DMPA) and benzoin as initiators via matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry. Analysis of the MALDI‐TOF spectra indicated that the two radical fragments generated upon pulsed laser irradiation show markedly different reactivity toward MMA: whereas the benzoyl fragment—common to both DMPA and benzoin—clearly participates in the initiation process, the acetal and benzyl alcohol fragments cannot be identified as end groups in the polymer. The complexity of the MALDI‐TOF spectrum strongly increased with increasing laser intensity, this effect being more pronounced in the case of benzoin. This indicates that a cleaner initiation process is at work when DMPA is used as the photoinitiator. In addition, the MALDI‐TOF spectra were analyzed to extract the propagation‐rate coefficient, kp, of MMA at ?34 °C. The obtained value of kp = 43.8 L mol?1 s?1 agrees well with corresponding numbers obtained via size exclusion chromatography (kp = 40.5 L mol?1 s?1). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 675–681, 2002; DOI 10.1002/pola.10150 相似文献