Phosphoproteome analysis of mouse liver using immobilized metal affinity purification and linear ion trap mass spectrometry

Since protein phosphorylation is a dominant mechanism of information transfer in cells, there is a great need for methods capable of accurately elucidating sites of phosphorylation. In recent years mass spectrometry has become an increasingly viable alternative to more traditional methods of phosphorylation analysis. The present study used immobilized metal affinity chromatography (IMAC coupled with a linear ion trap mass spectrometer to analyze phosphorylated proteins in mouse liver. A total of 26 peptide sequences defining 26 sites of phosphorylation were determined. Although this number of identified phosphoproteins is not large, the approach is still of interest because a series of conservative criteria were adopted in data analysis. We note that, although the binding of non-phosphorylated peptides to the IMAC column was apparent, the improvements in high-speed scanning and quality of MS/MS spectra provided by the linear ion trap contributed to the phosphoprotein identification. Further analysis demonstrated that MS/MS/MS analysis was necessary to exclude the false-positive matches resulting from the MS/MS experiments, especially for multiphosphorylated peptides. The use of the linear ion trap considerably enabled exploitation of nanoflow-HPLC/MS/MS, and in addition MS/MS/MS has great potential in phosphoproteome research of relatively complex samples. Copyright (C) 2004 John Wiley Sons, Ltd.

Photo-induced reactions in the ion-molecule complex Mg+-OCNC2H5

Ion - molecule complexes of magnesium cation with ethyl isocyanate were produced in a laser- ablation supersonic expansion nozzle source. Photo- induced reactions in the 1: 1 complexes have been studied in the spectral range of 230 - 410 nm. Photodissociation mass spectrometry revealed the persistent product Mg+ from nonreactive quenching throughout the entire wavelength range. As for the reactive channels, the photoproducts, Mg+OCN and C2H5+, were produced only in the blue absorption band of the complex with low yields. The action spectrum of Mg+(OCNC2H5) consists of two pronounced peaks on the red and blue sides of the Mg+ 3(2)P <-- 3(2)S atomic transition. The ground state geometry of Mg+ - OCNC2H5 was fully optimized at B3LYP/6- 31 - G** level by using GAUSSIAN 98 package. The calculated absorption spectrum of the complex using the optimized structure of its ground state agrees well with the observed action spectrum. Photofragment branching fractions of the products are almost independent of the photolysis photon energy for the 3P(x,y,z) excitations. The very low branching ratio of reactive products to nonreactive fragment suggests that evaporation is the main relaxation pathway in the photo- induced reactions of Mg+ (OCNC2H5). (C) 2003 American Institute of Physics.

Separation of peptides on mixed mode of reversed-phase and ion-exchange capillary electrochromatography with a monolithic column

The mixed mode of reversed phase (RP) and strong canon-exchange (SCX) capillary electrochromatography (CEC) based on a monolithic capillary column has been developed. The capillary monolithic column was prepared by in situ copolymerization of 2-(sulfooxy)ethyl methacrylate (SEMA) and ethylene dimethacrylate (EDMA) in the presence of porogens. The sulfate group provided by the monomer SEMA on the monolithic bed is used for the generation of the electroosmotic flow (EOF) from the anode to the cathode, but at the same time serves as a SCX stationary phase. A mixed-mode (RP/SCX) mechanism for separation of peptides was observed in the monolithic column, comprising hydrophobic and electrostatic interaction as well as electrophoretic migration at a low pH value of mobile phase. A column efficiency of more than 280000 plates/m for the unretained compound has been obtained on the prepared monoliths. The relative standard deviations observed for to and retention factors of peptides were about 0.32% and less than 0.71% for ten consecutive runs, respectively. Effects of mobile phase compositions on the EOF of the monolithic column and on the separation of peptides were investigated. The selectivity on separation of peptides in the monolithic capillary column could be easily manipulated by varying the mobile phase composition.

Immobilized metal-ion chelating capillary microreactor for peptide mapping analysis of proteins by matrix assisted laser desorption/ionization-time of flight-mass spectrometry

Peptide mass mapping analysis, utilizing a regenerable enzyme microreactor with metal-ion chelated adsorption of enzyme, combined with matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) was developed. Different procedures from the conventional approaches were adopted to immobilize the chelator onto the silica supports, that is, the metal chelating agent of iminodiacetic acid (IDA) was reacted with glycidoxypropyltrimethoxysilane (GLYMO) before its immobilization onto the inner wall of the fused-silica capillary pretreated with NH4HF2. The metal ion of copper and subsequently enzyme was specifically adsorbed onto the surface to form the immobilized enzyme capillary microreactor, which was combined with MALDI-TOF-MS to apply for the mass mapping analysis of nL amounts of protein samples. The results revealed that the peptide mapping could routinely be generated from 0.5 pmol protein sample in 15 min at 50degreesC, even 20 fmol cytochrome c could be well digested and detected.

A velocity map ion-imaging study on C2H5SH and C3H7SH photodissociation at 243 nm

Photodissociation dynamics Of C2H5SH, i-C-3-H7SH and n-C3H7SH at 243.1 nm were investigated using velocity map ion-imaging method. H-atom photolysis products were detected by a (2 + 1) resonance enhanced ionization scheme. Both the angular distribution and translational energy distribution of the H-atom elimination processes were determined from the ion images of the H-atom products. The experimental results indicate that the H-atom eliminations from these molecules are mainly direct and fast dissociation processes from a repulsive potential energy state. And a more statistical dissociation process that likely occurs oil the ground state via internal conversion has also been observed. Dissociation energies of the S-H bonds are also derived from the H-atom product translational energy distributions. (C) 2002 Elsevier Science B.V. All rights reserved.

Calibration of an audio-frequency ion trap mass spectrometer

A method for calibration of an audio-frequency (AF) ion trap mass spectrometer is described. The method is proposed to surmount the obstacle that there is a lack of a proper calibrant for mass spectrometers in the mass-to-charge ratio (m/z) range of 10(6) to 10(10). To calibrate such mass spectra, we determine the point of ejection, q(eject), on the stability diagram of the ion trap operated in a mass-selective axial instability mode. This is accomplished by measuring the radial secular frequencies (and therefore, the m/z value) of a single trapped particle using a light scattering method, followed by monitoring the action of particle ejection in real time to obtain the q(eject). A delayed ejection with q(eject) = 0.949 +/- 0.004 is found at a trap driving frequency of Ohm/2pi = 200-600Hz. Theoretical analysis for the origin of the delayed ejection indicates that the delay is predominantly resulted from the existence of multipole components in the fields due to trap imperfections. Inclusion of -3% of the octopole with respect to the basic quadrupole field can satisfactorily account for our observations. An m/z accuracy approaching 0.1% is attainable after proper calibration of the AF ion trap mass spectrometer. (Int J Mass Spectrom 214 (2002) 63-73) (C) 2002 Elsevier Science B.V. All rights reserved.

Proton transfer reactions within the pyridazine-methanol cluster ion

The multiphoton ionization of the hydrogen-bonding cluster pyridazine-methanol (C4H4N2-CH3OH) was studied using a time-of-flight mass spectrometer at the wavelengths of 355 and 532 nm. At both wavelengths, a series of protonated C4H4N2-(CH3OH)(n)-H+ cluster ions were obtained. Relevant ab initio calculations were performed with HF and B3LYP methods. Equilibrium geometries of both neutral and ionic C4H4N2-CH3OH clusters, and dissociation channels and dissociation energies of ionic clusters, are presented. The results show that when C4H4N2-CH3OH is vertically ionized, C4H4N2H+ and CH3O are the dominant products via proton transfer reaction. A high energy barrier makes another channel corresponding to the production of C4H4N2H+ and CH2OH disfavored. (C) 2002 Elsevier Science B.V. All rights reserved.

Ion recognition: application of symmetric and asymmetric schiff bases and their complexes for the fabrication of cationic and anionic membrane sensors to determine ions in real samples

Schiff base compounds refer to the branch of supra-molecules and can be used as sensing material in the construction of potentiometric ion selective electrodes (ISEs). This relatively modern field has been subject to extensive research in the period of 1999-2007 when more than 100 ISEs employing Schiff bases were constructed. The quantitative high-throughput detection of 29 cations and 7 anions has been demonstrated in various scientific branches, such as biomedicine, pharmacy, biochemistry, pharmacology, environmental chemistry, food technology, and agriculture. This review discusses Schiff base compounds and their applications in the design and development of ion selective sensors and microsensors.

Mercury selective electrochemical sensor based on a double armed crown ether as ionophore

PVC based membranes of a double armed crown ether, N, N'-dibenzyl, 1,4,10,13-tetraoxa-7, 16-diaza cyclooctadecane (I) as ionophore with sodium tetra phenyl borate (NaTPB) as anion excluder and with many plasticizing solvent mediators have been prepared and used for Hg(II) ion determination. The membrane with DBBP (dibutyl butyl phosphonate ) as plasticizer with various ingredients in the ratio PVC: I: NaTPB: DBBP (150: 12: 2: 100) shows the best results in terms of working concentration range (3.1x10-5-1.0x10-tM) with a Nernstian slope (29.0′0.5 mV/decade of activity). The electrode works in the pH range 2.1-4.5. The response time of the sensor is 15s and it can be used for about 4 months in aqueous as well as in non-aqueous medium. It has good stability and reproducibility. The potentiometric selectivity coefficient values for mono-, di-, and trivalent cations are tabulated. The sensor is highly selective for Hg2+ in the presence of normal interferents like cadmium, silver, sodium and iron.

Calibration of a solid-state copper ion-selective electrode in cupric ion buffers containing chloride

It is shown that near-Nernstian calibration slopes can be obtained with a Cu1.8Se electrode in a range of cupric ion buffers in spite of a high chloride content. Best results are obtained with the ligands ethylenediamine, glycine and histidine. The onset of cupric ion toxicity towards marine organisms falls within the pCu calibration range obtained with glycine, and the Cu1.8Se electrode could, therefore, be useful for monitoring cupric ion activity in bioassays in sea-water media.

Mercury(II) ion sensing with PVC-matrix based membrane sensors

Thiosemicarbazone derivatives have been used as ion carriers for the preparation of PVC-matrix based mercury(II)-selective membrane sensors. The electrodes give near-Nernstian responses in the linear concentration range of 1.0×10-1-5.0×10-6 M with detection limits of the order of 10-6 M. The stable potentiometric signals are obtained within a short time period of 20-25s. The effect of different plasticizers has been studied and dioctylsebacate (DOS) found to give a better response in comparison to other plasticizers. Selectivity coefficient values (log KPotHg,M) have been evaluated using fixed interference method. Better selectivity for mercury(II) ions is observed over many of the monovalent (Na+, K+ and NH4+) and divalent ions (Mg2+, Ca2+, Zn2+, Pb2+, Ni2+, Co2+, etc.). The sensors have also been used as indicator electrodes in potentiometric titration of mercury(II) ions with EDTA and its determination in synthetic water samples.

Synthesis and Metal-ion Binding Properties of New N2S4O2- and N2S5O2-Donor Macrocycles

Synthetic procedures for new mixed-donor macrocycle compounds were reported. The macrocyclic compounds were used in solvent extraction metal picrates such as Ag+, Hg2+, Cd2+, Zn2+, Cu2+, Ni2+, Mn2+, Pb2+, and Co2+. The metal picrate extractions were investigated at 25±0.1°C with the aid of UV-visible spectrometry. It was found that 6,7,9,10,12,13,23,24-octahydro-19H,26Hdibenzo[h,t](1,4,7,13,16,22,10,19) dioxatetrathiadiazasiclotetracosine-20,27(21H,28H)-dione showed selectivity towards Ag+, Hg2+, and Cd2+ among the other metals. The extraction constants (Log Kex) and complex compositions were determined for the Ag+ and Hg2+ complexes for this compound and 9,10,12,13,23,24,26,27,29,30-decahydro-5H,15H-dibenzo-[h,w][1,4,7,13,16,19,25-,10,22] dioxapentathiadiazacycloheptacosine-6,16(7H,17H)-dione.