Biomedical subjects
E R Williams
Publications and source records attributed to E R Williams.
Unimolecular reaction kinetics in the high-pressure limit without collisions.
Molecular activation by blackbody photons, first postulated in 1919 by Perrin, plays a dominant role in the unimolecular dissociation of large ions trapped at low pressure in a Fourier-transform mass spectrometer. Under readily achievable experimental conditions, molecular ions of the protein ubiquitin equilibrate with the blackbody radiation field inside the vacuum chamber. The internal energy of a population of these ions is given by a Boltzmann distribution. From the temperature dependence of unimolecular dissociation rate constants measured in the zero-pressure limit, Arrhenius activation parameters equal to those in the high-pressure limit are obtained.
Blackbody infrared radiative dissociation of bradykinin and its analogues: energetics, dynamics, and evidence for salt-bridge structures in the gas phase.
Blackbody infrared radiative dissociation (BIRD) spectra of singly and doubly protonated bradykinin and its analogues are measured in a Fourier-transform mass spectrometer. Rate constants for dissociation are measured as a function of temperature with reaction delays up to 600 s. From these data, Arrhenius activation parameters in the zero-pressure limit are obtained. The activation parameters and dissociation products for the singly protonated ions are highly sensitive to small changes in ion structure. The Arrhenius activation energy (E(a)) and pre-exponential (or frequency factor, A) of the singly protonated ions investigated here range from 0.6 to 1.4 eV and 10(5) to 10(12) s(-1), respectively. For bradykinin and its analogues differing by modification of the residues between the two arginine groups on either end of the molecule, the singly and doubly protonated ions have average activation energies of 1.2 and 0.8 eV, respectively, and average A values of 10(8) and 10(12) s(-1), respectively, i.e., the presence of a second charge reduces the activation energy by 0.4 eV and decreases the A value by a factor of 10(4). This demonstrates that the presence of a second charge can dramatically influence the dissociation dynamics of these ions. The doubly protonated methyl ester of bradykinin has an E(a) of 0.82 eV, comparable to the value of 0.84 eV for bradykinin itself. However, this value is 0.21 +/- 0.08 eV greater than that of singly protonated methyl ester of bradykinin, indicating that the Coulomb repulsion is not the most significant factor in the activation energy of this ion. Both singly and doubly protonated Lys-bradykinin ions have higher activation energies than the corresponding bradykinin ions indicating that the addition of a basic residue stabilizes these ions with respect to dissociation. Methylation of the carboxylic acid group of the C-terminus reduces the E(a) of bradykinin from 1.3 to 0.6 eV and the A factor from 1012 to 105 s(-1). This modification also dramatically changes the dissociation products. Similar results are observed for [Ala(6)]-bradykinin and its methyl ester. These results, in combination with others presented here, provide experimental evidence that the most stable form of singly protonated bradykinin is a salt-bridge structure.
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.
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.
Modeling the maximum charge state of arginine-containing Peptide ions formed by electrospray ionization.
A model for the gas-phase proton transfer reactivity of multiply protonated molecules is used to quantitatively account for the maximum charge states of a series of arginine-containing peptide ions measured by Downard and Biemann (Int. J. Mass Spectrom. Ion Processes 1995, 148, 191-202). We find that our calculations account exactly for the maximum charge state for 7 of the 10 peptides and are off by one charge for the remaining 3. These calculations clearly predict the trend in maximum charge states for these peptides and provide further evidence that the maximum charge state of ions formed by electrospray ionization is determined by their gas-phase proton transfer reactivity.
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.
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.
Molecular basis of a unique African variant (A-IV 5) of human apolipoprotein A-IV and its significance in lipid metabolism.
Human apolipoprotein A-IV (apoA-IV) exhibits a genetically determined structural polymorphism amenable to analysis by isoelectric focusing and immunoblotting techniques. We have determined the allele frequency and molecular basis of a unique ApoA-IV*5 allele which is widely distributed among blacks but is absent in other populations. The frequency of the ApoA-IV*5 allele in blacks (N = 308) was estimated to be 3.2%. In comparison to the common ApoA-IV*1 allele, analysis of coding and non-coding sequences of the ApoA-IV*5 allele revealed an in-frame insertion of 12 nucleotides near the carboxyl terminal region of the mature protein. The insertion involves an exact duplication of the second of the four repeats and codes for 4 amino acids glutamic acid (GAA), glutamine (CAG), glutamine (CAG), and glutamine (CAG) and is responsible for the charge shift of the the apoA-IV 5 isoform slightly toward the anode as compared to the wild type apoA-IV 1 isoform on the isoelectric focusing gel. This in-frame insertion occurs in a region which is highly conserved among rat, mouse, and humans. In addition to the 12 nucleotide insertion, the four individuals sequenced for the ApoA-IV*5 allele also revealed a same-sense mutation by replacing G to T at the third position of codon 316. Our preliminary data suggest that this unique black allele marker may be of potentially significance in studies of human lipid metabolism and in microevolution.
Hadamard transform measurement of tandem Fourier-transform mass spectra.
The simultaneous collection of multiple spectra using tandem (MS/MS) and multidimensional (MS/MS/MS) mass spectrometry from multiple precursors is demonstrated to yield correspondingly enhanced sensitivity. This approach utilizes Hadamard transform deconvolution and takes advantage of the multichannel dissociation capability of Fourier-transform mass spectrometry. By application of this to an 11-component mixture, the 11 spectra of the products of dissociating 11 different combinations of six of the component molecular ions are measured; Hadamard transformation yields individual spectra of the precursor ions exhibiting a signal-to-noise improvement of 1.8x over spectra measured separately, as predicted by theory. Precursor ion selection with high specificity and product formation with high abundance reproducibility are critical; spurious peaks resulting from imperfect reproducibility can be minimized by using simultaneous equation coefficients reflecting the degree of precursor dissociation. Extension of this technique to MSn spectra is demonstrated with simultaneous MS/MS/MS monitoring of three precursors and three daughters yielding nine spectra representing the nine possible dissociation pathways. For MSn spectra, coding the product relationships for each additional step (e.g., precursor----daughter, daughter----granddaughter) requires elimination of half of the remaining ions. No ions are lost for coding in an improved Hadamard approach in which the combined daughter spectrum of the selected half of the precursors is subtracted from that of the other half.
Fourier-transform mass spectrometry of large molecules by electrospray ionization.
The multiply charged ions produced by electrospray ionization of peptides of molecular masses up to 29 kDa have been successfully introduced into a Fourier transform mass spectrometer of unique capabilities for tandem mass spectrometry, large ion dissociation, and resolution. Electrospray ionization places an unusually high number of charges on a peptide yielding mass/charge (m/z) values of 600-1500; in this range at normal operating pressures (approximately 10(-9) torr; 1 torr = 133.3 Pa) Fourier-transform mass spectrometry resolving power is greater than 100,000. Although only 10(-7) torr pressure has been obtained with the initial interface, the resulting resolving power of 5000 makes possible the resolution of isotopic peaks of multiply charged ions. Mass measuring accuracies of a few daltons for molecular masses up to 17 kDa have also been achieved.
Californium-252 plasma desorption with Fourier transform mass spectrometry.
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Clinical curio: addiction to sherbet fountains.
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A comparison of acebutolol with methyldopa in hypertensive pregnancy.
Twenty pregnant women with mild to moderate hypertension were treated with either methyldopa or acebutolol, a beta-adrenergic blocking agent with cardioselectivity and intrinsic sympathomimetic activity, in a prospective open study. The two groups were comparable, although some selection bias may have been present. The dose of either drug was adjusted to attain a diastolic blood pressure of 80 mmHg or less, and 2 of the acebutolol group and 1 of the methyldopa group required the addition of hydralazine to achieve this. There were no still births or neo-natal deaths in either group. There was no difference discernible between the groups in duration of pregnancy, birth weight. Apgar score or placental weight, and no evidence of bradycardia, hypoglycaemia or respiratory difficulty in the babies born to mothers taking acebutolol. Fewer side-effects seemed to be present in the acebutolol group, and the mean period of hospitalization during pregnancy was 8 days in these patients compared with 14 days in the methyldopa group (p less than 0.01). The results of this pilot study suggest that acebutolol warrants further investigation as an effective and well-tolerated treatment of hypertension in pregnancy.
Retrospective self-diagnosis of toxic-shock syndrome.
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Lead screening in South Carolina.
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Effect of nutritional status on rat adipose tissue, muscle and post-heparin plasma clearing factor lipase activities: their relationship to triglyceride fatty acid uptake by fat-cells and to plasma insulin concentrations.
1. In rats in a variety of nutritional states, the adipose tissue clearing factor lipase activity is strongly, positively correlated with fat-cell triglyceride fatty acid uptake. 2. In the same animals, muscle clearing factor lipase activity is inversely correlated with the activity of the enzyme in adipose tissue and with the plasma insulin concentration. 3. In starved animals that are given glucose, adipose tissue clearing factor lipase activity is positively correlated with the plasma insulin concentration. 4. The effect of changes in nutritional status on the activity of clearing factor lipase in rat post-heparin plasma depends on the heparin dosage used. The administration of glucose, but not of fructose or sucrose, to starved rats alters the response to heparin injection towards that found in rats in the fed state.
The clearing-factor lipase activity of isolated fat-cells.
1. When fat-cells are isolated from the epididymal adipose tissue of 24h-starved rats and incubated at 25 degrees C in the presence of dialysed serum, glucose, insulin, amino acids and heparin, the total clearing-factor lipase acitivity of the incubation system increases progressively over a period of several hours. 2. All of the increase in activity is accounted for by the appearance of enzyme in the appearance of enzyme in the incubation medium and the fat-cell activity does not change significantly. Cycloheximids, at a concentration that prevents protein synthesis, does not affect the appearance of enzyme in the incubation medium, but the fat-cell enzyme activity is decreased in its presence. 3. The magnitude of the increase in total clearing factor lipase activity is unaffected by the omission of heparin from the medium. However, less enzyme is extracted in tis absence and the fat-cell activity increases. Cycloheximide again only affects the rise in cell activity and does not alter the activity in the incubation medium. 4. When serum in the incubation medium is replaced by casein, the distribution of enzyme between the cells and the medium is changed, but the magnitudes of the increases in total enzyme activity are similar. 5. These characteristics of the clearing-factor lipase response of isolated fat-cells differ in several respects from those observed earlier with intact adipose tissue from 24h-starved rats (Robinson & Wing, 1971; Cryer et al., 1973). The differences could be due, in part, to changes in the relative amounts of two different molecular forms of the enzyme that occur during the isolation of the fat-cells.