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Biomedical subjects

E R Williams

Publications and source records attributed to E R Williams.

At least 19 recordsLinked to original sources
PubMed2001

Supercharged protein and peptide ions formed by electrospray ionization.

The multiple charging of large molecules in electrospray ionization provides key advantages for obtaining accurate molecular weights by mass spectrometry and for obtaining structural information by tandem mass spectrometry and MS(n) experiments. Addition of glycerol or m-nitrobenzyl alcohol into the electrospray solutions dramatically increases both the maximum observed charge state and the abundances of the high charge states of protein and peptide ions. Adding glycerol to acidified aqueous solutions of cytochrome c shifts the most abundant charge state from 17+ to 21+, shifts the maximum charge state from 20+ to 23+, and shifts the average charge state from 16.6+ to 20.9+. Much less m-nitrobenzyl alcohol (<1%) is required to produce similar results. With just 0.7% m-nitrobenzyl alcohol, even the 24+ charge state of cytochrome c is readily observed. Similar results are obtained with myoglobin and (Lys)4. For the latter molecule, the 5+ charge state is observed in the electrospray mass spectrum obtained from solutions containing 6.7% m-nitrobenzyl alcohol. This charge state corresponds to protonation of all basic sites in this peptide. Although the mechanism for enhanced charging is unclear, it does not appear to be a consequence of conformational changes of the analyte molecules. This method of producing highly charged protein ions should be useful for improving the performance of mass measurements on mass spectrometers with performances that decrease with increasing m/z. This should also be particularly useful for tandem mass spectrometry experiments, such as electron capture dissociation, for which highly charged ions are desired.

Animals↗
PubMed2001

Psychiatric status, somatisation, and health care utilization of frequent attenders at the emergency department: a comparison with routine attenders.

Seventy-seven frequent attenders at an emergency department (ED) in an inner-city hospital in the UK (defined as seven or more visits in the previous 12 months) were compared with 182 patients who were attending the same department on a routine basis. Patients completed the Schedules for Clinical Assessment in Neuropsychiatry (SCAN) and the Short Form (SF)-36. Information was obtained on 64% of the frequent attenders and 45% underwent a detailed psychiatric assessment. Of the frequent attenders, 45% had psychiatric disorder and 49% had some form of an alcohol-related disorder. Compared with routine attenders, frequent attenders reported lower health status, had more psychiatric disorder (odds ratio: OR=8.2, 95% confidence interval: CI=3.8--18.1), had more general hospital admissions (OR=19.9, 95% CI=8.3--47.8), more psychiatric admissions (OR=167.5, 95% CI=9.5--2959.0), and more GP visits (95% CI for difference=-10.2 to -5.7). There was no evidence that frequent attenders had more somatisation than routine attenders. Specific treatment and management strategies need to be developed for this group of patients, although a substantial proportion may be difficult to engage in the treatment process.

Adolescent↗
PubMed2001

Gas-phase reactions of hydrated alkaline earth metal ions, M2+ (H2O)n (M = Mg, Ca, Sr, Ba and n = 4-7), with benzene.

Gas-phase reactions of hydrated divalent alkaline earth metal ions and benzene were investigated by electrospray ionization Fourier-transform mass spectrometry. Rate constants for solvent-exchange reactions were determined as a function of hydration extent for Mg2+, Ca2+, Sr2+, and Ba2+ clusters containing four to seven water molecules each. All of the strontium and barium clusters react quickly with benzene. Barium reacts slightly faster than the corresponding strontium cluster with the same number of water molecules attached. For calcium, clusters with four and five water molecules react quickly, whereas those with six and seven water molecules do not. Magnesium with four water molecules reacts quickly, but not when five through seven water molecules are attached. The slow reactivity observed for some of these clusters indicates that the cation-pi interaction between the metal ion and benzene is partially screened by the surrounding water molecules. The reactivity of magnesium with seven water molecules is intermediate that of the hexa- and pentahydrate and the tetrahydrate. This result is consistent with the seventh water molecule being in the outer shell and much more weakly bound. The unusual trend in reactivity observed for magnesium may be due to the presence of mixed shell structures observed previously. These results are the first to provide information about the relative importance of cation-pi interactions in divalent metal ions as a function of metal hydration extent. Such studies should also provide a model and some insight into the relative binding affinities of divalent metal ions to aromatic residues on peptides and proteins.

Benzene↗
PubMed2000

Medical clearance of psychiatric patients.

Patients with primarily psychiatric complaints commonly present to emergency departments. The challenges to emergency medicine physicians are to distinguish functional from organic disease and to address any underlying medical comorbidities. The key elements of this medical "clearance" evaluation of psychiatric patients are discussed. The tremendous importance of the history and physical examination are highlighted, as is judicious use of laboratory and radiographic testing. Toxicology testing is specifically addressed.

Causality↗
PubMed2000

Effects of solvent on the maximum charge state and charge state distribution of protein ions produced by electrospray ionization.

The effects of solvent composition on both the maximum charge states and charge state distributions of analyte ions formed by electrospray ionization were investigated using a quadrupole mass spectrometer. The charge state distributions of cytochrome c and myoglobin, formed from 47%/50%/3% water/solvent/acetic acid solutions, shift to lower charge (higher m/z) when the 50% solvent fraction is changed from water to methanol, to acetonitrile, to isopropanol. This is also the order of increasing gas-phase basicities of these solvents, although other physical properties of these solvents may also play a role. The effect is relatively small for these solvents, possibly due to their limited concentration inside the electrospray interface. In contrast, the addition of even small amounts of diethylamine (<0.4%) results in dramatic shifts to lower charge, presumably due to preferential proton transfer from the higher charge state ions to diethylamine. These results clearly show that the maximum charge states and charge state distributions of ions formed by electrospray ionization are influenced by solvents that are more volatile than water. Addition of even small amounts of two solvents that are less volatile than water, ethylene glycol and 2-methoxyethanol, also results in preferential deprotonation of higher charge state ions of small peptides, but these solvents actually produce an enhancement in the higher charge state ions for both cytochrome c and myoglobin. For instruments that have capabilities that improve with lower m/z, this effect could be taken advantage of to improve the performance of an analysis.

Algorithms↗
PubMed1999

Hydration of gas-phase ions formed by electrospray ionization.

The hydration of gas-phase ions produced by electrospray ionization was investigated. Evidence that the hydrated ions are formed by two mechanisms is presented. First, solvent condensation during the expansion inside the electrospray source clearly occurs. Second, some solvent evaporation from more extensively solvated ions or droplets is apparent. To the extent that these highly solvated ions have solution-phase structures, then the final isolated gas-phase structure of the ion will be determined by the solvent evaporation process. This process was investigated for hydrated gramicidin S in a Fourier-transform mass spectrometer. Unimolecular dissociation rate constants of isolated gramicidin S ions with between 2 and 14 associated water molecules were measured. These rate constants increased from 16 to 230 s-1 with increasing hydration, with smaller values corresponding to magic numbers.

Electrochemistry↗
PubMed1999

Dissociation energies of deoxyribose nucleotide dimer anions measured using blackbody infrared radiative dissociation.

The dissociation kinetics of deprotonated deoxyribose nucleotide dimers were measured using blackbody infrared radiative dissociation. Experiments were performed with noncovalently bound dimers of phosphate, adenosine (dAMP), cytosine (dCMP), guanosine (dGMP), thymidine (dTMP), and the mixed dimers dAMP.dTMP and dGMP.dCMP. The nucleotide dimers fragment through two parallel pathways, resulting in formation of the individual nucleotide or nucleotide + HPO3 ion. Master equation modeling of this kinetic data was used to determine threshold dissociation energies. The dissociation energy of (dGMP.dCMP-H)- is much higher than that for the other nucleotide dimers. This indicates that there is a strong interaction between the nucleobases in this dimer, consistent with the existence of Watson-Crick hydrogen bonding between the base pairs. Molecular mechanics simulations indicate that Watson-Crick hydrogen bonding occurs in the lowest energy structures of (dGMP.dCMP-H)-, but not in (dAMP.dTMP-H)-. The trend in gas phase dissociation energies is similar to the trend in binding energies measured in nonaqueous solutions within experimental error. Finally, the acidity ordering of the nucleotides is determined to be dTMP < dGMP < dCMP < dAMP, where dAMP has the highest acidity (largest delta Gacid).

Algorithms↗
PubMed1998

Separation and characterization of amines from individual atrial gland vesicles of Aplysia californica.

Several amine-containing components of individual vesicles from the atrial gland of Aplysia californica were identified with capillary electrophoresis (CE). On-line derivatization with naphthalene-2,3-dicarboxaldehyde was performed, and the derivatized amine-containing components were detected with laser-induced fluorescence (LIF). Amino acids, including taurine, that had not been determined previously in atrial gland vesicles were observed by using CE-LIF, and their identities were confirmed with CE, HPLC, NMR, and electrospray ionization mass spectrometry. The finding that taurine is packaged and stored into secretory vesicles supports the hypothesis that taurine may exhibit neuromodulatory activity. The bioactive peptides, well-known to be in atrial gland vesicles, were detected in lysed vesicle samples fractionated with HPLC and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. These peptides were also observed in single-vesicle runs with CE-LIF. The atrial gland vesicles (ranging from 0.5 to 2 microns diameter and 65 aL to 4 fL volume, respectively) studied in this work represent the smallest biological entities to be analyzed chemically on an individual basis.

Amines↗
PubMed1998

Analysis of isomeric mixtures using blackbody infrared radiative dissociation: determining isomeric purity and obtaining individual tandem mass spectra simultaneously.

A new method that makes possible, for the first time, simultaneous acquisition of individual dissociation mass spectra of isomeric ions in mixtures is presented. This method exploits the exquisite sensitivity of blackbody infrared radiative dissociation kinetics to minor differences in ion structure. Instead of separating precursor ions based on mass (isomers have identical mass), fragment ions are related to their original precursor ions on the basis of rate constants for dissociation. Mixtures of the peptide isomers des-R1 and des-R9 bradykinin are dissociated simultaneously at several temperatures. By fitting the kinetic data to double-exponential functions, the dissociation rate constant and abundance of each isomer in the mixture are obtained. To overcome the difficulty of fitting double-exponential functions, a novel global analysis method is used in which several dissociation data sets collected at different temperatures are simultaneously fit. The kinetic data measured at multiple temperatures are modeled with the preexponentials (corresponding to the abundance of each isomer) as "global" parameters which are constant for all data sets and the exponentials (rate constants) as "local" variables which differ for each data set. The use of global parameters significantly improves the accuracy with which abundances and dissociation rate constants of each individual compound can be obtained from the mixture data. Fragment ions produced from a mixture of these two isomers are related back to their respective precursor ions from the kinetic data. Thus, not only can the composition of the isomeric mixture be determined but an individual tandem mass spectrum of each component in the mixture can be obtained.

Bradykinin↗
PubMed1998

Probing single secretory vesicles with capillary electrophoresis.

Secretory vesicles obtained from the atrial gland of the gastropod mollusk Aplysia californica were chemically analyzed individually with a combination of optical trapping, capillary electrophoresis separation, and a laser-induced fluorescence detection. With the use of optical trapping, a single vesicle that had attoliters (10(-18) liters) of volume was introduced into the tapered inlet of a separation capillary. Once the vesicle was injected, it was lysed, and its components were fluorescently labeled with naphthalene-2, 3-dicarboxaldehyde before separation. The resultant electropherograms indicated distinct variations in the contents of single vesicles.

Amines↗
PubMed1998

Blackbody infrared radiative dissociation of oligonucleotide anions.

The dissociation kinetics of a series of doubly deprotonated oligonucleotide 7-mers [d(A)7(2-), d(AATTAAT)2-, d(TTAATTA)2-, and d(CCGGCCG)2-] were measured using blackbody infrared radiative dissociation in a Fourier-transform mass spectrometer. The oligonucleotides dissociate first by cleavage at the glycosidic bond leading to the loss of a neutral nucleobase, followed by cleavage at the adjacent (5') phosphodiester bond to produce structurally informative a-base and w type ions. From the temperature dependence of the unimolecular dissociation rate constants, Arrhenius activation parameters in the zero-pressure limit are obtained for the loss of base. The measured Arrhenius parameters are dependent on the identity of the nucleobase. The process involving the loss of an adenine base from the dianions, d(A)7(2-), d(AATTAAT)2-, and d(TTAATTA)2- has an average activation energy (Ea) of approximately 1.0 eV and a preexponential factor (A) of 10(10) s-1. Both guanine and cytosine base loss occurs for d(CCGGCCG)2-. The average Arrhenius parameters for the loss of cytosine and guanine are Ea = 1.32 +/- 0.03 eV and A = 10(13.3 +/- 0.3) s-1. No loss of thymine was observed for mixed adenine-thymine oligonucleotides. Neither base loss nor any other fragmentation reactions occur for d(T)7(2-) over a 600 s reaction delay at 207 degrees C, a temperature close to the upper limit accessible with our instrument. The Arrhenius parameters indicate that the preferred cleavage sites for mixed oligonucleotides of similar mass-to-charge ratio will be strongly dependent on the internal energy of the precursor ions. At low internal energies (effective temperatures below 475 K), loss of adenine and subsequent cleavage of the adjacent phosphoester bonds will dominate, whereas at higher energies, preferential cleavage at C and G residues will occur. The magnitude of the A factors < or = 10(13) s-1 measured for the loss of the three nucleobases (A, G, and C) is indicative of an entropically neutral or disfavored process as the rate limiting step for this reaction.

Chemical Phenomena↗
PubMed1997

Effects of charge state on fragmentation pathways, dynamics, and activation energies of ubiquitin ions measured by blackbody infrared radiative dissociation.

Blackbody infrared radiative dissociation spectra of the (M + 5H)5+ through (M + 11H)11+ ions of the protein ubiquitin (8.6 kDa) formed by electrospray ionization were measured in a Fourier-transform mass spectrometer. The 5+ ion dissociates exclusively by loss of water and/or ammonia, whereas the 11+ charge state dissociates only by formation of complementary y and b ions. These two processes are competitive for intermediate charge state ions, with the formation of y and b ions increasingly favored for the higher charge states. The y and b ions are formed by cleavage of the backbone amide bond on the C-terminal side of acidic residues exclusively, with cleavage adjacent to aspartic acid favored. Thermal unimolecular dissociation rate constants for the dissociation of each of these charge states were measured. From the temperature dependence of these rates, Arrhenius activation parameters in the rapid energy exchange limit are obtained. The activation energies (Ea) and preexponential factors (A) for the 5+, 8+, and 9+ ions are 1.2 eV and 10(12) s-1, respectively. These values for the 6+ and 7+ ions are 0.9-1.0 eV and 10(9) s-1, and those for the 10+ and 11+ ions are 1.6 eV and 10(16)-10(17) s-1. Thus, with the exception of the 5+ ion, the higher charge states of ubiquitin have larger dissociation activation energies than the lower charge states. The different A factors observed for production of y and b ions from different precursor charge states indicate that they are formed by different mechanisms, ranging from relatively complex rearrangements to direct bond cleavages. These results clearly demonstrate that the relative dissociation rates of large biomolecule ions by themselves are not necessarily a reliable indicator of their relative dissociation energies, even when similar fragment ions are formed.

Infrared Rays↗
PubMed1996

Conformations and folding of lysozyme ions in vacuo.

Proton transfer reactivity of isolated charge states of the protein hen egg-white lysozyme shows that multiple distinct conformations of this protein are stable in the gas phase. The reactivities of the 9+ and 10+ charge state ions, formed by electrospray ionization of "native" (disulfide-intact) and "denatured" (disulfide-reduced) solutions, are consistent with values calculated for ions in their crystal structure and fully denatured conformations, respectively. Charge states below 8+ of both forms, formed by proton stripping, have similar or indistinguishable reactivities, indicating that the disulfide-reduced ions fold in the gas phase to a more compact conformation.

Animals↗
PubMed1996

Proton transfer reactivity of large multiply charged ions.

Charge-charge interactions dramatically influence the dissociation and proton transfer reactivity of large multiply protonated ions. In combination with tandem mass spectrometry, proton transfer reactions have been used to determine the charge state of an ion and to increase the effective mass resolution of electrospray ionization mass spectra. A model for the proton transfer reactivity of multiply protonated ions, in which protons are assigned to specific sites in an ion based on the intrinsic reactivity of the site and the sum of point-charge Coulomb interactions between charges, is discussed. In combination with experimentally measured rates of proton transfer to bases of known gas-phase basicity, information about the intramolecular electrostatic interactions, gas-phase ion conformation and maximum charge state of an ion produced by electrospray ionization can be obtained.

Animals↗
PubMed1995

The social implications of lower urinary tract reconstruction performed during childhood.

OBJECTIVE: To compare the social effects of urinary diversion, undiversion and orthotopic bladder reconstruction performed during childhood. PATIENTS AND METHODS: Of 99 patients treated at the Wessex Centre for Paediatric Surgery between 1960 and 1993, 46 (16 with a urinary diversion, eight with an undiversion and 22 with bladder reconstruction) were interviewed using a standardized questionnaire. Information was collected about the types and results of surgery, the medical support received and the social effects of the different treatments. RESULTS: By day, continence or only occasional wetting was achieved in 13 patients with diversions, all those with undiversions and 16 of those with reconstructions. At night, 13 patients with diversions, seven with undiversions and 18 with reconstructions were dry or only occasionally wet. Re-operation rates were higher in those with reconstruction and undiversion. Only five of the diversion group were satisfied with their management compared to all patients in the other two groups. The social effects in terms of employment, schooling, independence, body image and social interactions were also better in those with undiversions and reconstructions. CONCLUSIONS: The social effects of undiversion and bladder reconstruction were better than those following urinary diversion despite the higher re-operation rates and the need for a rigid regimen of post-operative care. However, the need for continuing medical support in this group of patients cannot be over emphasized, and the vital role of the urological nurse specialist is stressed.

Adolescent↗
PubMed1994

Hypervariable polymorphism of APO(a) in blacks and whites as reflected by phenotyping.

Genetic polymorphism at the apolipoprotein(a) structural locus was investigated in 203 American blacks using a high-resolution SDS-agarose electrophoresis method followed by immunoblotting, and the gene frequency data were compared with a previously screened American white sample using the same method. Between the two samples, a total of 27 discrete APO(a) allelic isoforms have been documented; of these, 24 were common to both groups. Of the 203 blacks screened, APO(a) immunoreactive isoforms were detected in 201, with a total of 101 distinct phenotypes (67 (33%) single-banded and 134 (67%) double-banded). A similar level of gene diversity was observed at the APO(a) locus in blacks (93%) and whites (94%). Despite having a similar number of alleles and a similar level of gene diversity, the frequencies of some APO(a) alleles were significantly different between blacks and whites. Overall, the frequencies of large-size APO(a) alleles, associated with lower LP(a) levels, were significantly lower (P < 0.0001), while the frequencies of medium-size APO(a) alleles, associated with intermediate LP(a) levels, were significantly higher (P < 0.0001) in blacks than in whites. However, the frequencies of small-size alleles, associated with higher LP(a) levels, were comparable between the two race groups. These data indicate that the observed differences in mean LP(a) levels between whites and blacks may be accounted for by the size variation at the APO(a) structural locus.

Adolescent↗