Biomedical subjects

B T Bulliman

Publications and source records attributed to B T Bulliman.

14 recordsLinked to original sources

PubMed1992

Urea exchange across the human erythrocyte membrane measured using 13C NMR lineshape analysis.

The 13C NMR spectrum of 13C-urea in a suspension of human red cells of reduced mean cell volume was observed to contain partially resolved resonances arising from the intra- and extracellular populations of the compound. It was shown that at 25 degrees C and a magnetic field strength of 9.4 T, the rate of exchange of urea between the intra- and extracellular populations was such that the NMR lineshape was sensitive to a change in the rate of 13C-urea exchange, induced either by the addition of the urea transport inhibitor phloretin, or by the addition of 12C-urea. Total lineshape analysis of 13C NMR spectra of 13C-urea in red cell suspensions containing different concentrations of 12C-urea resulted in a weighted mean estimate for the Km and Vmax for urea equilibrium exchange from three experiments of 44 +/- 18 mM and 3.1 +/- 0.6 x 10(-8) mol cm-2 s-1, respectively (the errors denote the weighted mean standard deviations). These estimates of Km and Vmax were significantly lower than previous values reported in the literature and determined using other techniques.

Adult↗

PubMed1990

Kinetic analysis of the human erythrocyte glyoxalase system using 1H NMR and a computer model.

1H NMR was used with methylglyoxal, purified by an HPLC technique, to study the kinetics of the human erythrocyte glyoxalase system. 1H NMR enabled the direct measurement of the time-dependent changes in concentrations of the two hydrates of methylglyoxal, which have not previously been directly measurable, as well as measurement of substrates and products of the glyoxalase enzyme system in the human red blood cell. A computer model of the reaction scheme was developed and NMR data numerically analyzed, thus allowing a complete kinetic description of the reactions. The rate constants describing the chemical equilibria between the hydrated species of methylglyoxal were determined by this numerical analysis or by a saturation-transfer technique, and found to be much slower (by several orders of magnitude) than previously determined by other methods. The kinetic parameters describing the enzyme-catalyzed reactions were also determined from experiments using a dilute haemolysate that was added to solutions of methylglyoxal and reduced glutathione (GSH). The maximal velocity of glyoxalase 1 is threefold greater (Vmax = 70.4 +/- 4.7 mmol.min-1.1 packed cells-1) than glyoxalase 2(Vmax = 24 +/- 5 mmol.min-1.1 packed cells-1) and it exhibits threefold-greater affinity for its substrate (Km = 0.46 +/- 0.04 mM) than the second enzyme (Km = 1.5 +/- 0.4 mM). Both enzymes are subject to competitive inhibition; glyoxalase 1 by reduced glutathione (KiGSH = 7.88 +/- 0.16 mM) and glyoxalase 2 by the hemithioacetal (HTA) of methylglyoxal and GSH (KiHTA = 0.29 +/- 0.04 mM).

Erythrocytes↗

PubMed1990

Evaluation of an electrochemical model of erythrocyte pH buffering using 31P nuclear magnetic resonance data.

When erythrocytes are suspended in a solution of known composition the resultant values of such basic cell parameters as volume and pH are difficult to predict. To facilitate such predictions, we developed a mathematical model describing the passive transmembrane distribution of permeant species; three simultaneous equations were produced. Certain essential data required for the model were determined experimentally; these included the pH dependence of the charge on the hemoglobin molecule and the variation of the osmotic coefficient of hemoglobin with cell volume. Finally, cells were added to various solutions, and then titrated to produce a wide pH range (pH 6-8). We measured the resultant cell volume, cellular and extracellular pH using both conventional and 31P NMR methods. The expected equilibrium values of these electrochemical parameters were also calculated by solving (numerically) the three model equations. The accuracy of the model simulations was evaluated by direct comparison of calculated and experimentally determined values.

Acid-Base Equilibrium↗

PubMed1990

Comparison of biochemical simulations using integrators derived from "Adomian" decomposition with traditional numerical methods.

Comparisons are made between some traditional numerical integrators and integration using "Adomian" power series solutions to the ordinary differential equations. These are initial investigations to determine the viability of their application to the simulation of large complex metabolic pathways. A small set of test equations was employed to represent the types of problems encountered in biochemical applications. It was found that the "Adomian" method is as accurate as the numerical methods and, for 'nonstiff' equations or for small simulation times, the "Adomian" method is often more efficient. The results suggest that it may be worthwhile refining this method for biochemical simulations for situations where the traditional numerical methods fail.

Computer Simulation↗

PubMed1990

Computer simulation of the pentose-phosphate pathway and associated metabolism used in conjunction with NMR experimental data from human erythrocytes.

A computer-based model of the metabolism of sugar phosphates by human erythrocytes has been developed to assist in the understanding of the biochemical transformations occurring in the pentose phosphate pathway. These transformations are reflected in the changes, with time, of the relative intensities of the metabolite peaks apparent in 1H, 13C and 31P NMR spectra. The deterministic model consists of 79 reactions interconnected in a defined structure and characterized by 155 rate constants. It also includes 17 different enzymes, 69 enzyme forms, 32 metabolites, and initial value of time and concentration of each of the reactants. The differential equations describing the time-dependence of the concentrations of the reactants are generated and then solved by using the computer program BIOSSIM, which is designed to solve arrays of "stiff" differential equations. We synthesized [1-13C]D-ribose 5-phosphate and used 13C and 31P NMR to monitor its transformation into various intermediates of the pentose phosphate pathway, after the addition of diluted haemolysates which had previously been depleted of nicotinamide- and adenine-nucleotides. The concentrations of several of the reactants were able to be quantified, while other peaks in both the 13C and 31P spectra are yet to be assigned with confidence. There was reasonable qualitative agreement between some aspects of the computer simulation of the proposed metabolic system and the experimental data.

Biotransformation↗

PubMed1989

Magnetic potential and field gradients of a model cell.

The magnetic potential within and outside a nucleated cell placed in a uniform magnetic field is described for a model consisting of two concentric diamagnetic spheres. The analytical description of the magnetic potential in and around a system consisting of a finite number of concentric diamagnetic spheres in a uniform magnetic field was derived. The solution was employed to calculate the field gradients outside and inside a model chicken red blood cell. The form and magnitude of the gradients provide a theoretical basis on which to discuss experimental results relating to the attenuation of signals obtained using proton nuclear magnetic resonance spectroscopy with chicken erythrocyte suspensions. The form of the magnetic field, field difference and field gradients in the external medium of a cell suspension was simulated for a distribution of spheres in a uniform magnetic field, such as might occur in an idealised dilute cell suspension.

Animals↗

PubMed1989

Perturbation of homogeneous magnetic fields by isolated single and confocal spheroids. Implications for NMR spectroscopy of cells.

Analytical expressions for the magnetic potential and the magnetic field strength vector in cells modelled as isolated confocal prolate and oblate spheroids have been derived. The important results which emerged from the analysis are that the magnetic field in the central spheroid, in a series of confocal spheroids, is always uniform; but its magnitude depends upon the orientation of the spheroids relative to the external field. Therefore, the NMR line-shape derived from an internal solute in a population of sparsely distributed spheroids, with random orientation of the members, is a superposition of Lorentzians; the resulting 'complicated' line shape may often appear to be Gaussian. This spectral phenomenon is at least part of the explanation for the non-Lorentzian character of NMR line-shapes in the spectra of many biological samples. Quantitative analysis of the NMR line-shape of an appropriate intracellular solute can in principal yield the orientational distribution of a dilute suspension of cells of uniform size and shape.

Cell Aggregation↗

PubMed1988

A series expression for the surface area of an ellipsoid and its application to the computation of the surface area of avian erythrocytes.

Knowledge of the surface area of cells is necessary for biophysical studies in which the permeability coefficient of a cell-type for a solute is defined. Under the microscope, avian erythrocytes have the appearance of an oval discus usually with a central elongated nucleus. The dimensions of these cells have been obtained for a large range of species over the past century. However, estimates of the surface areas have been obtained using mathematically simplistic models such as flattened circular cylinders. We modelled red cells of the domestic chicken (Gallus domesticus) as ellipsoids using the previously published dimensions to obtain the three semi-axis lengths. Although the mathematical expression for the volume of an ellipsoid is well known, an expression for the surface area is not. We present a general expression for the surface area of an ellipsoid that is a power series involving elliptic integrals and functions; the latter being rapidly evaluated by computer using standard series expressions. Our estimates of area are compared with earlier ones and those obtained by numerical integration of the surface.

Animals↗

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

In vivo determination of ATP in tumors using 31P inversion spin transfer.

The in vivo exchange kinetics of creatine kinase in the hind leg muscle of rats containing a transplanted mammary adenocarcinoma has been investigated using 31P magnetic resonance spectroscopy. Using a solenoid coil, the adenosine triphosphate (ATP) resonances arising from the tumor could be distinguished from ATP resonances arising from the muscle surrounding the tumor by use of inversion spin transfer techniques. This procedure affords a specific method of evaluating ATP metabolism of tumors in vivo.

Adenocarcinoma↗

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

Use of inversion spin transfer to monitor creatine kinase kinetics in rat skeletal muscle in vivo.

A simple multipulse sequence has been used to monitor creatine kinase kinetics in rat skeletal muscle in vivo. Using these procedures, the forward (ATP synthesis) and reverse fluxes (phosphocreatine synthesis) have been calculated to be 8.98 +/- 0.6 and 10.7 +/- 0.8 mumoles/g wet wt/s (n = 5) respectively. These results suggest that in resting skeletal muscle most of the gamma ATP observed in 31P NMR spectra is cytosolic and rapidly exchanging with phosphocreatine. The high flux rates reflect the high catalytic capacity of creatine kinase in skeletal muscle.

Adenosine Triphosphate↗

PubMed1982

Systemic arterial hemodynamics in the diamond python Morelia spilotes.

Studies of pulsatile systemic arterial hemodynamics were conducted in 10 diamond python snakes to test the hypothesis that body shape--through spatial dispersion of peripheral reflecting sites--is an important determinant of impedance patterns and of pulse wave contour. Findings support the hypothesis. Flow patterns in the aortic roots were similar to those in humans, sheep, dogs, rabbits, and guinea pigs, but in contrast to larger animals, little change in flow contour was seen in other arteries. Pressure wave contour was similar in all systemic arteries from which records were taken with no secondary diastolic wave under any circumstances. Impedance patterns at different sites showed none of the fluctuations that in other animals are attributable to discrete wave reflection. Discrete proximal wave reflection at the confluence of aortic arches was minimal. Data are explicable on the basis of widely distributed peripheral reflecting sites--a consequence of the snake's long and tapered body.

Animals↗