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At least 109 records · Page 6Linked to original sources
PubMed1994

Mass measurement accuracy of matrix-assisted laser desorbed biomolecules: a Fourier-transform ion cyclotron resonance mass spectrometry study.

The use of binary matrices and internal calibrants to improve the mass measurement accuracy in matrix-assisted laser desorption ionization (MALDI) with Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry is described. Binary matrices enhance the analyte ion yield and enable a complete MALDI-FTICR mass spectrum to be obtained from a single laser shot. The advantage of single-laser-shot data acquisition is that it eliminates line-broadening due to shot-to-shot frequency variations. It is shown that unresolved product ions, mainly due to loss of H2O and/or NH3, shift the centroid of an unresolved multi-component peak. A mass measurement accuracy of 12 ppm was obtained for the bovine insulin [M+H]+ ion using melittin as an internal calibrant.

Animals↗
PubMed1994

Detection limits for matrix-assisted laser desorption of polypeptides with an external ion source Fourier-transform mass spectrometer.

Sensitivity in the low-femtomole range with mass resolution greater than 20,000 is demonstrated for several polypeptides analyzed by a mass spectrometer that pairs matrix-assisted laser desorption/ionization (MALDI) and Fourier-transform mass spectrometry (FTMS). The compounds investigated were substance P, renin substrate, melittin, the B-chain of bovine insulin, and bovine insulin. Standard solutions of the polypeptides were prepared with 30% acetonitrile+water, and micropipettes were used to transfer small amounts (1-20 fmol) to a sample probe. The samples were embedded in a large excess of matrix material (2,5-dihydroxybenzoic acid) and ionized by a pulse from an excimer laser. The FTMS instrument used for these experiments has the MALDI source in a separate chamber outside the magnetic field. Ions are extracted from the source and transported by an RF-only quadrupole ion guide to an FTMS analyzer cell mounted in the homogeneous region of a 6.5 T superconducting magnet. The high sensitivity of MALDI-FTMS is due, in part, to the high transfer efficiency of the ion guide, even for ions with a wide range of kinetic energies. The ion guide is easy to use because there are only two adjustments (RF amplitude and DC offset voltage), and unlike electrostatic ion transport means, alignment of it with the axis of the magnetic field is not critical. The mass resolution and sensitivity of MALDI-FTMS is compared with that of MALDI done with time-of-flight, magnetic sector, and quadrupole ion-trap mass spectrometers.

Amino Acid Sequence↗
PubMed1994

Optimization by mass spectrometry of a tryptophan-specific protein cleavage reaction.

Mass spectrometry has been used to define the reaction of BNPS-skatole (3-bromo-3-methyl-2-(o-nitrophenylsulfenyl)indolenine) with selected proteins and peptides, confirming the cleavage of the protein chain at tryptophan residues, characterizing the products, and identifying the side reactions. A short procedure for carrying out the cleavage reaction with minimal side reactions is presented.

Alkylation↗
PubMed1995

Thermal decomposition kinetics of protonated peptides and peptide dimers, and comparison with surface-induced dissociation.

Rate constants for the unimolecular decomposition of peptide monomer and dimer ions by thermal and surface-induced dissociation (SID) are measured and compared. Rate constants for thermal dissociation are measured in a heated wide-bore capillary flow reactor attached in front of the capillary leading into the mass spectrometer. Thermal decomposition of the leucine enkephalin ion (YGGFL)H+ is observed between 600 and 680 K with rate constants of 20-200 s-1, and yields many of the same fragments as SID at 35 eV, although with different relative intensities. The thermal decomposition yields the Arrhenius parameters Ea = 38.3 kcal/mol, log A = 15.7. The decomposition of the monomer and dimer ions are also observed by using SID on C18 and fluorinated hydrocarbon surfaces, with rate constants of 2 x 10(4) to 40 x 10(4) s-1. The SID activated monomer ions are assigned equivalent temperatures of 710-840 K by extrapolation of the thermal activation parameters. The protonated dimer ion (YGGFL)2 H+ decomposes thermally at 500-540 K to yield the monomer ion. The dimer also decomposes by SID at low collision energies 10-20 eV on both surfaces to yield the monomer ion, and at much higher energies of 60-80 eV to yield fragments identical to the decomposition of the monomer. The large energy requirement for fragmentation from the dimer is due to energy deposition into more degrees of freedom plus the additional energy required for dissociation of the dimer to the monomer.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed2004

A modified internal lock-mass method for calibration of the product ions derived from sustained off-resonance irradiation collision-induced dissociation using a Fourier transform mass spectrometer.

A modified internal lock-mass calibration method is introduced for improving the mass measurement accuracy of the product ion spectra derived from sustained off-resonance irradiation collision-induced dissociation (SORI-CID) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. This method involves an initial external calibration of the Fourier transform mass spectrometer to obtain the initial A- and B-terms for the equation (f(i) = A/(m/z)(i) + B). The A-term is adjusted by using an empirical relationship between the up-shift of the A-term and the pulse-gas duration, whereas the B-term is adjusted by using the mass of the unfragmented precursor ion from the SORI-CID mass spectrum of the unknown sample as internal lock-mass. These adjusted A- and B-terms are then used to provide exact mass SORI-CID calibration for the unknown sample. The modified internal lock-mass method achieved average mass measurement accuracy of approximately 3 ppm which is significantly better than that of the conventional internal lock-mass calibration ( approximately 9 ppm) and is approaching that of the internal calibration ( approximately 2 ppm) and requires no addition of internal calibrant or instrumental modifications.

Angiotensin II↗
PubMed2001

A cylindrical capacitor ionization source: droplet generation and controlled charge reduction for mass spectrometry.

A cylindrical capacitor ionization source was used in conjunction with corona discharge charge reduction for generation of singly charged ions for mass spectrometric analysis. The source consists of a fused-silica capillary threaded with a platinum wire and placed inside a stainless steel tube. Application of an electric potential to the wire results in the production of a linear stream of charged droplets when an aqueous solution is pumped through the capillary. Subsequent solvent evaporation yields ions, providing a continuous ion source for mass spectrometry. Passage of the ions through a corona discharge charge reduction chamber permits reduction of the charge state to predominantly singly charged species, facilitating analysis of DNA and protein mixtures. The change from production of multiply charged ions to production of singly charged ions is extremely simple, requiring only modulation of the voltage applied to the corona discharge electrode. A simple technique for construction of the ionization source is reported.

Animals↗
PubMed2006

Combined infrared multiphoton dissociation and electron-capture dissociation using co-linear and overlapping beams in Fourier transform ion cyclotron resonance mass spectrometry.

A novel set-up for Fourier transform ion cyclotron resonance mass spectrometry (FTICR) is reported for simultaneous infrared multiphoton dissociation (IRMPD) and electron-capture dissociation (ECD). An unmodified electron gun ensures complete, on-axis overlap between the electron and the photon beams. The instrumentation, design and implementation of this novel approach are described. In this configuration the IR beam is directed into the ICR cell using a pneumatically actuated mirror inserted into the ion-optical path. Concept validation was made using different combinations of IRMPD and ECD irradiation events on two standard peptides. The ability to perform efficient IRMPD, ECD and especially simultaneous IRMPD and ECD using lower irradiation times is demonstrated. The increase in primary sequence coverage, with the combined IRMPD and ECD set-up, also increases the confidence in peptide and protein assignments.

Amino Acid Sequence↗
PubMed2006

Direct high-resolution peptide and protein analysis by desorption electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.

We report the first coupling of a desorption electrospray ionization (DESI) ion source to Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS) for high-resolution protein analysis. The DESI FT-ICR-MS source design is described in detail along with preliminary data obtained on peptides and proteins ranging from 1 to 5.7 kDa.

Bradykinin↗
PubMed1993

Interaction of heme with amphiphilic peptides: use of hemin-CN to probe the interaction of calmodulin with its target peptides.

UNLABELLED: The interaction of heme with several amphiphilic peptides has been studied by absorption and fluorescence spectroscopy. The binding can be followed by the changes in the absorption spectrum of the heme group or by the decrease in the peptide tryptophan fluorescence due to energy transfer to the heme. Despite their small size, ranging from 26 residues for melittin to 14 for mastoporan, a high affinity for heme-CO and hemin-CN (Kd < 100 nM) may be observed. Spectral shifts in the absorption peaks and appreciable geminate recombination after photodissociation of CO from the complex peptide-heme-CO suggest the formation of a heme pocket, as for the natural heme proteins. APPLICATION: hemin-CN can be used as a probe for the interaction of calmodulin with these target peptides. Amphiphilic peptides such as melittin bind to calmodulin with a high (nM) affinity. While both the peptide and calcium-bound calmodulin bind heme-CO, only the peptide binds hemin-CN. These interactions permit studies of the competition between hemin-CN and calmodulin for binding to the peptide: while hemin-CN quenches the melittin tryptophan fluorescence, addition of calmodulin to the [melittin*hemin-CN] complex displaces the hemin-CN and the melittin tryptophan fluorescence is recovered.

Amino Acid Sequence↗
PubMed1994

Regulation of the plasma membrane type III phosphatidylinositol 4-kinase by positively charged compounds.

The effects of positively charged compounds on a plasma membrane, type III phosphatidylinositol 4-kinase were studied. To determine whether the enzyme would respond differently to the compounds in a membrane-associated versus a soluble state, both the plasma membrane and solubilized (released by 0.01% (v/v) Triton X-100) PI 4-kinase were used. Spermidine, spermine, polylysine, cardiotoxin, melittin, and histone stimulated the solubilized PI 4-kinase but had little effect on or weakly stimulated the membrane-associated PI 4-kinase. Polyarginine inhibited membrane-associated PI 4-kinase 75% and inhibited the solubilized PI 4-kinase 30%, indicating that charge alone was not sufficient for activation. Polyarginine also eliminated the activation of the solubilized PI 4-kinase by a PI 4-kinase activator protein, PIK-A49. Calmodulin, a common calcium-binding protein, at micromolar levels strongly inhibited solubilized PI 4-kinase activity but did not inhibit membrane-associated PI 4-kinase activity. The inhibition of the solubilized PI 4-kinase by calmodulin was calcium independent. Calcium alone (1 microM-0.1 mM) inhibited PI 4-kinase activity only slightly (< 30%). The differential effects of the positively charged compounds on the solubilized and membrane-associated PI 4-kinase were not due to substrate availability because both enzymes were assayed in the presence of excess PI (0.6 mM) and 0.3% (v/v) Triton X-100. The data suggest that positively charged compounds affected the enzyme activity not only by interacting with the substrates or products of the reaction but also by interacting with the PI 4-kinase or regulatory components in the plasma membrane.

1-Phosphatidylinositol 4-Kinase↗
PubMed1999

Oxidative modification of glutamine synthetase by 2,2'-azobis(2- amidinopropane) dihydrochloride.

In the present study, we examined the pattern of protein modification elicited by alkylperoxyl radicals and alkylperoxides. To this end, we exposed glutamine synthetase (GS) and the peptide melittin to solutions containing 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), which is known to decompose in aqueous, aerobic solutions to yield alkyl radicals and alkylperoxides. Under our conditions, pH 7.4, 37 degrees C, the AAPH-dependent formation of alkylhydroperoxide increased linearly with time and led to 40% inactivation of GS in 1 h and to complete inactivation in 4 h. Complete inactivation was associated with the loss of 2 of 16 histidine residues, 6 of 17 tyrosine residues, 5 of 16 methionine residues, and all of the tryptophan residues (2 residues) per subunit. Inactivation of GS was associated also with some protein fragmentation and the formation of some higher molecular weight aggregates. Exposure of GS to AAPH led also to the generation of protein carbonyl derivatives (0.34 mol/mol subunit) and to formation of a significant amount (0.038 mol/mol subunits) of quinoprotein derivatives. To investigate the mechanism of tryptophan modification, the 26-amino-acid peptide, melittin, which contains one tryptophan but no histidine, tyrosine, or methionine residues, was treated with AAPH. N-Formylkynurenine was identified as the major product of tryptophan oxidation in melittin.

Amidines↗
PubMed2000

Secretion and purification of recombinant beta1-4 galactosyltransferase from insect cells using pFmel-protA, a novel transposition-based baculovirus transfer vector.

The palette of transfer vectors available for generation of recombinant baculoviruses based on transposition-mediated recombination has been enlarged by constructing the pFmel-protA vector. The pFmel-protA plasmid includes the honeybee melittin secretion signal and a Staphylococcus aureus protein A fusion protein tag, which allows the secretion and purification of recombinant proteins. Using this system, the human beta1-4 galactosyltransferase-I protein was expressed in Sf9 insect cells at a level ranging from 22 to 28 U (4.8 to 6.0 mg)/L. The protein A tag enabled a simple monitoring of recombinant protein expression by enzyme-linked immunosorbent assay and Western blotting. Single step purification was achieved by immunoglobulin G affinity chromatography achieving a recovery yield of 28% and a specific activity of 1.9 U per mg of recombinant protein.

Amino Acid Sequence↗
PubMed2001

Melittin exerts multiple effects on the release of free fatty acids from L1210 cells: lack of selective activation of phospholipase A2 by melittin.

Melittin is known as a phospholipase A2 (PLA2) activator, but the selectivity of its effect on PLA2 is uncertain. We examined the selectivity of melittin effect on the release of free fatty acids (FFAs) from L1210 cells using various inhibitors. A systemic lipid analysis by HPLC and GLC revealed that melittin induced release of various FFAs including saturated, monounsaturated, and polyunsaturated FFAs. Various PLA2 inhibitors examined exerted only minimal effects on the melittin-induced arachidonic acid (AA) and palmitic acid (PAL) releases. Specific inhibitors of phosphatidylinositol-phospholipase C (U73122) and diacylglycerol lipase (RHC80267) exerted significant inhibitory effects on both AA and PAL releases. These results suggest that melittin-induced FFA release is most likely due to multiple participations of various types of lipases. Since BAPTA/AM, an intracellular Ca2+ chelator, did not influence the FFA release, the Ca2+ influxed by melittin appeared not to be a key factor for the FFA release. The mimicking of the melittin-induced FFA release by digitonin, a membrane-permeabilizing agent, implies that the membrane-perturbing action of melittin is likely the cause of the FFA release. Melittin also induced release of multiple FFAs from other cell lines including P388D1 and HL60. The rapid melittin-stimulated phospholipase D (PLD) observed in L1210 cells appeared not directly related to the steady release of FFA, as indicated by the fact that the PLD was not blocked by RHC80267. In view of melittin's multiple effects on the composition of cellular lipids, we conclude that melittin does neither exclusively release any single FFA nor selectively activate PLA2 in L1210 cells. The problem of using melittin as a PLA2 activator is discussed.

Animals↗
PubMed1993

Phospholipase A2 activation influences the processing and secretion of the amyloid precursor protein.

The phospholipase A2 (PLA2) inhibitors quinacrine, manoalide and scalaradial inhibit the carbachol-stimulated secretion of the amyloid precursor protein (APP) from cells transfected with the human m1 muscarinic receptor. Conversely, activation of PLA2 by melittin increases secretion of an apparently immature species of APP from these cells. These results implicate PLA2 in regulating APP processing and secretion, which may have important implications for understanding the pathogenesis of Alzheimer's Disease.

Amyloid beta-Protein Precursor↗
PubMed1994

The relationship between size of a presecretory protein and extent of signal-recognition-particle-mediated arrest of its translation.

Small eukaryotic presecretory proteins, such as preprocecropinA, prepromelittin, and prepropeptideGLa, are transported into mammalian microsomes both with the aid of ribosome and signal recognition particle (SRP) and independently of these ribonucleoprotein particles. Typically, synthetic extensions of these precursor proteins show the phenotype of naturally occurring large presecretory proteins. However, it was shown that small truncated forms of naturally occurring large presecretory proteins are not transport competent or transport competent only in the presence of the two ribonucleoprotein particles. In order to directly address this apparent paradox, we studied the sensitivities of nascent polypeptide chains, related to preprocecropinA and prepromelittin, to SRP-mediated arrest of elongation and compared them with synthetic extensions of various length.

Animals↗