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Biomedical subjects

B E Chapman

Publications and source records attributed to B E Chapman.

At least 55 records · Page 3Linked to original sources
PubMed1990

Fluoride transmembrane exchange in human erythrocytes measured with 19F NMR magnetization transfer.

19F NMR spectra of sodium fluoride in suspensions of human erythrocytes were seen to yield separate resonances for the F- populations inside and outside the cells. Selective saturation of the magnetization of the intracellular population gave rise to transfer of that saturation to the extracellular population. The extent of magnetization transfer was high and it was blocked by the capnophorin (band 3) anion exchange inhibitor 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS). A series of magnetization-inversion transfer experiments was carried out for the range of intracellular fluoride concentrations of 11 mM to 136 mM and analysed using one-dimensional 'overdetermined' exchange analysis. This yielded an estimate of the equilibrium exchange Michaelis constant and maximal velocity of 27 +/- 3 mM and 180 +/- 5 x 10(-16) mol cell-1 s-1, respectively. There was no alteration of exchange flux of fluoride at an intracellular concentration of 49 mM in the presence of 50 mM glucose; thus suggesting no interaction between glucose and anions in capnophorin-mediated exchange of solutes.

Erythrocyte Membrane↗
PubMed1990

Negative sexual experiences with men among heterosexual women and lesbians.

Survey responses on traumatic experiences with men were compared from 50 matched pairs of heterosexual women and lesbians. Prior research has implied that lesbians have had more traumatic experiences with men than heterosexual women. The purpose of this study was to test the hypothesis that lesbians would report more negative sexual experiences with men than heterosexual women. The findings of the present study did not support this hypothesis. The only significant difference found between the two groups was that heterosexual women were more likely to report multiple categories of traumatic experiences and lesbians were more likely to report experiences in only one category of trauma. Contrary to prior studies, these results indicate that previous traumatic experiences with men may not be a significant factor in the development of sexual orientation.

Adult↗
PubMed1988

31P magnetization transfer in the phosphoglyceromutase-enolase coupled enzyme system.

The rate of exchange of phosphoryl groups between 2-phosphoglycerate, 3-phosphoglycerate and phosphoenolpyruvate by the coupled phosphoglyceromutase-enolase enzyme system using one- and two-dimensional 31P NMR spectroscopy was measured. Magnetization exchange in one-dimensional experiments was achieved by saturation transfer with selective irradiation at both one and two sites in this three-site exchange system using the DANTE pulse sequence. The two-dimensional magnetization exchange experiment avoids the need to selectively saturate at one or more frequencies which may be difficult in complex exchange systems. Analysis of the two-dimensional exchange experiment by the back transformation method yielded exchange rate constants in good agreement with the saturation transfer method.

Animals↗
PubMed1988

Mutarotase equilibrium exchange kinetics studied by 13C-NMR.

The rates of exchange between the alpha- and beta-anomers of D-[1-13C]glucose, at equilibrium catalyzed by porcine kidney mutarotase (EC 5.1.3.3), were measured using 13C-NMR spin-transfer procedures. This entailed inversion-transfer and saturation-transfer experiments, and two-dimensional exchange spectroscopy (2D EXSY). The concentration and temperature dependences of the fluxes were studied; equilibrium exchange Michaelis constants, and the activation energy of the catalyzed reaction were thereby measured.

Carbohydrate Epimerases↗
PubMed1988

Now that they're yours: post-acquisition assessment.

What the administrator survey provides in a unique way is meaningful and immediately useful information about the status of facilities, whether recently acquired or already owned, that takes into account the complexity of providing quality service in long-term care. Facilities can be reassessed after a period of time, and repeatedly over time, so that the management team can evaluate its success in addressing the priorities established in previous surveys and shift its efforts as priorities change. This process keeps a "finger on the pulse" of the organization throughout the acquisition process and beyond, so that valuable management time and effort is expended where it will be most beneficial to the company's profitability and future success.

Data Collection↗
PubMed1987

Glucose transport in human erythrocytes measured using 13C NMR spin transfer.

We present the results of a new NMR-based procedure for measuring the fast transmembrane exchange of D-[1-13C]glucose in human erythrocytes. The method relies on different rates of exchange between the alpha- and beta-anomers of glucose inside and outside the cells; the rate outside the cells is greatly increased by the addition of mutarotase to the suspension. Theory is developed to describe nuclear-spin transfer in the present system and is used to analyse the data to yield estimates of transmembrane-exchange rate constants and their statistical uncertainties. For a total glucose concentration of 25.5 mmol/l at 40 degrees C the first order efflux rate constants for the alpha- and beta-anomers were 1.20 +/- 0.40 s-1 and 0.71 +/- 0.30 s-1, respectively.

Biological Transport↗
PubMed1987

Proposed model of lesbian identity development: an empirical examination.

A 42-question written survey was administered to 197 women, approximately 96% of whom were self-identified lesbians, for the purpose of gathering information about their experiences from first awareness of lesbian identity to their current status. Descriptive data are presented which seem to suggest that lesbian identity is present prior to the individual's recognition of incongruency between her feelings and those of non-lesbians, and that the process of self-labeling occurs through interaction with the non-lesbian world. The term lesbian identity is discussed and defined. The findings of this study are, in part, described in the framework of a proposed Model of Lesbian Identity Awareness and Self-Labeling which is currently undergoing further investigation.

Adult↗
PubMed1987

Fast transmembrane exchange in red cells studied with NMR.

13C NMR, with two fundamentally different procedures, was used to measure the H13CO3- permeability coefficient (P) of human erythrocytes. The values of P (approximately 3 X 10(-4) cm s-1) were similar to those obtained by other, non-NMR methods. A third procedure was used with 31P NMR to measure the permeability coefficient of human erythrocytes for the non-electrolyte dimethyl methylphosphonate; the effects on transmembrane exchange of varying haematocrit and butanol were studied.

Bicarbonates↗
PubMed1986

Bicarbonate exchange kinetics at equilibrium across the erythrocyte membrane by 13C NMR.

The rate of exchange of 13C-labelled bicarbonate across the membranes of human erythrocytes in suspension, at thermal and chemical equilibrium, was measured using 13C NMR spectroscopy: the permeability coefficient (3.34 X 10(-4) cm s-1) agrees well with previous values obtained with other methods. Data analysis was complicated by the need to consider the Donnan ratio of the charged species inside and outside the cells. This work appears to be the first, involving the present NMR procedure, for studying fast membrane transport of a molecule other than water.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1986

Intracellular pH in stored erythrocytes. Refinement and further characterisation of the 31P-NMR methylphosphonate procedure.

Methylphosphonate in conjunction with 31P-NMR spectroscopy was used for the measurement of transmembrane delta pH in human erythrocytes stored at 4 degrees C for up to 5 weeks in a nutrient medium. Intra- and extracellular pH was determined using calibration curves based on the pH-dependent separation between the NMR resonances of methylphosphonate and orthophosphate (Pi). A comprehensive statistical procedure is presented for the determination of the variance of NMR-based pH estimates. The entry of methylphosphonate into erythrocytes was more rapid at low pH and uptake was fully inhibited by the band 3 reagent, disodium 4,4-diisothiocyano-2,2'-disulphonic acid stilbene. The distribution ratio of methylphosphonate concentration inside and outside the cells was used to calculate the membrane potential; the analysis depends on a consideration of the Donnan equilibrium for an anion with one or two charges. Furthermore, the analysis does not depend on the pH estimates but relies solely on concentration estimates. The chemical shift of methylphosphonate was not subject to the variations associated with specific intracellular binding encountered with many other phosphorus compounds, including Pi. On the other hand, the ionic strength dependence of the chemical shift of methylphosphonate, contrary to earlier reports, is comparable in magnitude (but opposite in sign) to that of Pi.

Blood Preservation↗
PubMed1986

Intra- and extraerythrocyte pH at 37 degrees C and during long term storage at 4 degrees C: 31P NMR measurements and an electrochemical model of the system.

A 31P NMR method based on pH dependent variation of the chemical-shift-difference between the resonances of orthophosphate and methylphosphonate was used to measure simultaneously intracellular pH (pHi) and extracellular pH (pHc) during long term storage of erythrocytes; pH was determined at both 4 degrees C and 37 degrees C. An equation describing the equilibrium distribution of membrane-permeant ions was derived by consideration of the electrochemical and osmotic constraints in the RBC suspension. Calculations using the model-equation and the measured pHi yielded the Donnan ratio and therefore pHo; the relationship between experimentally determined pHi and pHo values was accurately predicted by the model. Sensitivity analysis of the model-equation revealed that the observed increase in transmembrane pH gradient during storage is principally due to the alteration of the total net charge of intracellular (poly)-anions.

2,3-Diphosphoglycerate↗
PubMed1985

Direct observation of the NAD glycohydrolase reaction in human erythrocytes using NMR spectroscopy.

The hydrolysis of NAD by the extracellular membrane-associated enzyme NAD glycohydrolase was shown to be readily followed in concentrated suspensions of human erythrocytes using 1H spin-echo nuclear magnetic resonance spectroscopy (NMR). The maximal rate of the reaction was determined and the inhibitory effect of nicotinamide was confirmed by direct NMR observation. In addition, arginine, ergothioneine and iodoacetate did not influence the reaction rate. 31P NMR analyses of reaction media from whole cells showed that no extraneous degradation of NAD occurred and the only phosphate-containing product was ADP-ribose.

Adenosine Diphosphate Ribose↗
PubMed1985

Regeneration of phosphorylated metabolites in stored erythrocytes in an open perfusion system: studies using 31P NMR spectroscopy.

Human erythrocytes were maintained at high haematocrit in a metabolically functional state for several hours in a thermodynamically open perfusion apparatus. The concentrations of ATP and 2,3-bisphosphoglycerate (2,3-DPG) and pH were continuously monitored before and after metabolic perturbations by using 31P NMR; the monitoring was achieved with a 31P flow-through probe. Methylphosphonate was added to plasma perfusion medium as a phosphorus concentration standard and as a 31P NMR pH probe molecule. The rates of decline of ATP and 2,3-DPG levels in fresh cells in a glucose-free medium were measured as were the rates of reformation in response to a 'rejuvenation' medium. Also, rates of ATP and 2,3-DPG synthesis during perfusion with Krebs bicarbonate-0.5 mmol/l glucose and perfusion with pooled plasma were measured in cells that had been previously stored at 4 degrees C for 5 weeks.

2,3-Diphosphoglycerate↗
PubMed1984

A proton nuclear magnetic resonance study of gamma-glutamyl-amino acid cyclotransferase in human erythrocytes.

Spin-echo NMR spectroscopy was shown to be a reliable technique for the monitoring of the in situ cleavage of gamma-Glu-Ala by gamma-glutamyl-amino acid cyclotransferase in whole erythrocytes and hemolysates. Of particular importance was the difference in chemical shifts between peptide resonances and those of the constituent amino acids. Using lysates of varying dilution, it was shown that the specific activity of the enzyme was not concentration-dependent, thus suggesting a lack of cytosolic low-molecular-weight-effectors or enzyme dissociation. Furthermore, the initial velocities of the reaction as a function of substrate concentration obeyed Michaelis-Menten kinetics with a Km = 2.0 +/- 0.3 mmol/l and Vmax = 137 +/- 7 mmol/h/l of cell water in 1H2O medium. Similar analysis in 2H2O medium revealed a solvent kinetic isotope effect of 1.9 +/- 0.4 at low substrate concentrations. The implications of this observation for the mechanism of the reaction are discussed. Cleavage of the peptide by a suspension of intact erythrocytes was at a rate 300 times less than the corresponding lysate flux, thus indicating the rate limitation by transport in the coupled system.

Acyltransferases↗
PubMed1984

The relationship between glucose concentration and rate of lactate production by human erythrocytes in an open perfusion system.

A thermodynamically open system, based on an assembly of capillaries with semi-permeable walls was constructed in order to study glycolysis in human erythrocytes in high haematocrit suspensions. A phenomenological expression for the rate of lactate production as a function of glucose concentration was obtained. The rate was measured under steady-state conditions with low substrate concentrations (approx. 50 mumol/l). In a corresponding closed system, this concentration of glucose would be exhausted within a few minutes. A mathematical model of the whole system consisted of five differential equations, and involved parameters relating to flow rates, volumes of reaction chambers, the rates of lactate efflux from erythrocytes and the expression for the rate of lactate production by red cells. The binding of [14C]pyruvate to haemoglobin and the rate of efflux of [14C]lactate from red cells were measured to yield additional information for the model. The concentrations of ATP and 2,3-bisphosphoglycerate were measured during the perfusion experiments, and a detailed analysis of a model of red cell hexokinase was carried out; the former two compounds inhibit hexokinase and alter the apparent Km and Vmax for glucose in vivo. These steady-state parameters were similar to the glucose concentration at the half-maximal rate of lactate production and the maximal rate, respectively. These findings are consistent with the known high control-strength for hexokinase in glycolysis in human red cells. The practical and theoretical validation of this perfusion system indicates that it will be valuable for NMR-based studies of red cell metabolism using a flow-cell in the spectrometer.

2,3-Diphosphoglycerate↗
PubMed1984

31P NMR spin-transfer in the phosphoglyceromutase reaction.

The rate of exchange of phosphoryl groups between 2- and 3-phosphoglycerate catalysed by (a) high concentrations (approximately equal to 5.0 mg protein ml-1) of rabbit muscle phosphoglyceromutase and (b) lysed human erythrocytes was measured using saturation and inversion transfer techniques with 31P-NMR spectroscopy. This is the first reported application of these techniques to a study of this particular enzymic reaction either in vitro or in situ in a cell cytosol. Selective irradiation of resonances was achieved by the DANTE pulse sequence which had not previously been used for spin-transfer studies. New equilibrium exchange theory was developed for the simplest model of a two-reactant enzyme-catalysed reaction and this was used to calculate turnover rates for the enzymes. There was a close similarity between the turnover rates calculated from the spin-transfer data obtained from the systems in vitro and in situ and those obtained by conventional enzymic assays, at low enzyme concentrations. This suggested an absence of any homogeneous enzyme-enzyme interactions which modify the kinetics at high protein concentrations either in lysates or in the system in vitro.

Animals↗