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Biomedical subjects

C M Jackson

Publications and source records attributed to C M Jackson.

At least 19 recordsLinked to original sources
PubMed1992

Study of high-affinity interactions by quantitative affinity chromatography. Analytical expressions in terms of total ligand concentration.

Analytical expressions are derived for the description of ligand-facilitated and ligand-retarded desorption of partitioning solute in terms of total ligand concentration in quantitative affinity chromatography. Their application is then illustrated by consideration of results from recycling partition equilibrium studies of the heparin-facilitated desorption of thrombin from heparin-Sepharose, and of the competition between methyl-alpha-D-mannoside and p-nitrophenyl-alpha-D- mannoside for concanavalin A immobilized on CPG-170. Finally, published frontal affinity chromatographic data for the NADH-dependent elution of rabbit muscle lactate dehydrogenase from oxamate-Sepharose are reanalysed using these equations to demonstrate the characterization of a system reflecting the binding of a solute-ligand complex to an affinity matrix. This investigation extends the scope of quantitative affinity chromatography to include not only the study of solute-ligand interactions governed by larger binding constants but also the characterization of interactions in which the partitioning solute and ligand are both macromolecular, and eliminates the need for prior dialysis to establish the free ligand concentration required for application of earlier analytical expressions.

Animals↗
PubMed1992

An audit of acute asthma admissions to a respiratory unit.

A criterion based audit was performed on 90 admissions with acute asthma to a specialist respiratory unit using the guidelines set by the British Thoracic Society. Three main areas were audited including: documentation of severity markers in the case notes on admission, acute treatment given on admission, and further investigations performed. Case notes were found to be deficient in documentation of objective severity markers such as peak expiratory flow rate (52% recorded) and blood gases (72% recorded), as well as subjective markers such as speech (27%), air entry (58%) and exhaustion (4%). Of the total 90 admissions, 78% were identified as having at least three out of five objective markers for acute severe asthma. Most of these severe cases (93%) were given corticosteroids but none were prescribed greater than 35% concentration of inspired oxygen. The majority of admissions had a chest radiograph (87%), and 56% had measurement of serum potassium. These results show that even in a specialised respiratory unit, guidelines such as those produced by the British Thoracic Society are not in general being adhered to. It also indicates that assessment of severity is inadequate, particularly for peak flow measurement, and that management is deficient in established treatments such as the use of high flow oxygen. As a result of the audit, a severity marker stamp for the case notes along with guidelines for treatment have been implemented in order to improve the quality of care delivered to patients admitted with acute asthma.

Acute Disease↗
PubMed1991

Preferential ligand binding to multi-state acceptor systems: comparisons of the calcium-binding and dimerization characteristics of prothrombin and fragment 1.

Consideration is given to the interactions of a ligand with self-associating acceptor systems for which preferential binding is an ambiguous term in that ligand-mediated self-association does not necessarily imply a greater binding constant for polymeric acceptor--even in instances where binding sites are preserved in the self-association process. This dilemma is shown to arise in situations involving the binding of ligand to monomeric and polymeric forms of an acceptor that also coexist in equilibrium with inactive isomeric states. For example, the ten-fold increase in the measured dimerization constant for prothrombin Fragment 1 in the presence of a saturating concentration of Ca2+ ion may well reflect the existence of a 12% greater binding constant for the interaction of metal ion with dimeric acceptor. However, that result, as well as the detailed form of the sigmoidal binding curve, are also reasonably described by another extreme model in which the monomeric and dimeric forms of the acceptor possess equal affinities for Ca2+ ion. Likewise, the fact that the same experimental dimerization constant applies to prothrombin and its Ca(2+)-saturated complex does not preclude the possibility that the active form of dimeric zymogen exhibits a 12% greater affinity for metal ion. Numerical simulations have established that characterization of the dimerization behaviour as a function of free ligand concentration should allow greater discrimination between such models of the interplay between calcium binding and self-association of prothrombin and Fragment 1. Finally, by illustrating the likelihood that the disparity in self-association behaviour of prothrombin and Fragment 1 merely reflects minor differences in the relative magnitudes of isomerization constants and/or binding constants for monomeric and dimeric states of the two acceptors, the present investigation serves to allay concern about the validity of employing the proteolytic fragment as a model of the intact zymogen.

Calcium↗
PubMed1991

Effects of thermodynamic nonideality in kinetic studies: evidence of an expanded intermediate complex in the inactivation of thrombin by antithrombin III.

The technique of competitive chromogenic substrate hydrolysis is used to examine the inhibitory effects of sucrose and glycerol on the inactivation of thrombin by antithrombin III. This inhibition is attributed to the existence of a slight increase in volume/asymmetry associated with formation of the thrombin-antithrombin complex that subsequently undergoes covalent modification in an irreversible inactivation step. Partial reversal of the equilibrium step is thus considered to result from the effects of molecular crowding in the highly concentrated environment that is generated by the inclusion of these small insert solutes.

Antithrombin III↗
PubMed1991

Use of quantitative affinity chromatography for characterizing high-affinity interactions: binding of heparin to antithrombin III.

The versatility of quantitative affinity chromatography (QAC) for evaluating the binding of macromolecular ligands to macromolecular acceptors has been increased substantially as a result of the derivation of the equations which describe the partitioning of acceptor between matrix-bound and soluble forms in terms of total, rather than free, ligand concentrations. In addition to simplifying the performance of the binding experiments, this development makes possible the application of the technique to systems characterized by affinities higher than those previously amenable to investigation by QAC. Addition of an on-line data acquisition system to monitor the concentration of partitioning solute in the liquid phase as a function of time has permitted the adoption of an empirical approach for determining the liquid-phase concentration of acceptor in the system at partition equilibrium, a development which decreases significantly the time required to obtain a complete binding curve by QAC. The application of these new QAC developments is illustrated by the determination of binding constants for the interactions of high-affinity heparin (Mr 20,300) with antithrombin III at three temperatures. Association constants of 8.0 +/- 2.2 x 10(7), 3.4 +/- 0.3 x 10(7), and 1.0 +/- 0.2 x 10(7) M-1 were observed at 15, 25, and 35 degrees C, respectively. The standard enthalpy change of -4.2 +/- 0.6 kcal/mol that is calculated from these data is in good agreement with a reported value obtained from fluorescence quenching measurements.

Antithrombin III↗
PubMed1979

On the molecular-weight-dependence of the anticoagulant activity of heparin.

The inactivation of thrombin and factor Xa by antithrombin was determined in the presence of heparin fractions of different molecular weights and with high affinity for antithrombin. The ability to potentiate the inactivation of either coagulation factor increased with increasing length of the polysaccharide chain.

Antithrombin III↗
PubMed1979

Measurement of phospholipid monolayer surface potentials at a hydrocarbon-electrolyte interface.

The phospholipid monolayer spread at a hydrocarbon-electrolyte interface can be used as a model system for the plasma membrane and its properties and structure probed by measurements of surface pressure and surface potential. To facilitate such studies, (i) the theory of the vibrating plate (Kelvin) method of measuring surface potentials is reëxamined and a new interpretation given for the potentials measured and (ii) a new apparatus for performing these measurements is described. The theory and apparatus are illustrated by measurements on films of distearoyl phosphatidylcholine at the interface between 2,2,4-trimethylpentane (isooctane) and 0.1 M NaCl.

Cell Membrane↗
PubMed1979

Phospholipid monolayers at the hydrocarbon-electrolyte interface. The interrelation of film potential and film pressure.

Measurements of surface pressure of surface potential are reported for films of distearoyl phosphatidylcholine (density range: 0.15--2.65 . 10(18) molecules/m2) spread at the interface between 2,2,4-trimethylpentane and 100 mM NaCl. Low density behavior of the surface pressure is explained using classical viral theory. The behavior of the surface potential is qualitatively explained for all densities in terms of the dipole moments associated with the carboxyl groups and headgroups of the phosphatidylcholine.

Electrolytes↗
PubMed1978

Properties of the factor Xa binding site on human platelets.

The affinity (Ka) of human coagulation Factor Xa for thrombin-treated (to stimulate the release reaction) platelets has been determined to be 3 to 4 x 10(10) M-1 by equilibrium binding studies using 125I-labeled Xa. The binding of Factor Xa to platelets results in an increase of 300,000-fold in the apparent enzymatic activity of Xa in the conversion of prothrombin to thrombin. The activity of platelet surface Xa is approximately 15-fold greater than that observed with optimum concentrations of bovine Factor V and phospholipids in place of platelets. Ca2+ is required for the Xa-platelet interaction; the optimum concentration is 2.5 mM. Related coagulation factors, including Factor X, Factor IXa, diisopropylphosphoryl Factor Xa, and prothrombin do not complete with Factor Xa for the Xa binding sites. The rate of thrombim formation at saturating amounts of Xa is directly proportional to the number of platelets from 1 x 10(7) to 5 x 10(8) platelets/ml. Factor Xa bound to platelets is not inactivated by antithrombin III. An antibody that inhibits both human and bovine coagulation Factor V activity blocks both Xa binding to released platelets and the rapid thrombin formation associated with this binding, suggesting that Factor V from platelets is involved in the Xa-platelet interaction.

Binding Sites↗
PubMed1978

Comparison of methods for detecting specific IgM antibody in infants with congenital rubella.

Serum specimens from 14 infants with congenital rubella were examined for specific IgM antibody by six different methods. IgM-containing fractions were separated either by sucrose density-gradient centrifugation or by gel filtration through Sephadex G-200, and were then tested by the indirect immunofluorescence technique and by the haemagglutination-inhibition (HI) test (long-and short-incubation methods). Immunofluorescence staining of density-gradient fractions detected specific IgM in all 14 infants. The HI test (long method), applied to density-gradient fractions, was almost as sensitive, detecting antibody in 13 infants; the short method was less sensitive. The gel-filtration technique proved to be generally less satisfactory than sucrose density-gradient centrifugation. Evidence was obtained for the occurrence of as yet unclassified non-specific inhibitors in the serum of some infants. These inhibitors were deposited with the IgM on sucrose-density gradients and they could have been mistaken for rubella-specific IgM antibody, particularly in the HI test (long method).

Antibodies, Viral↗
PubMed1978

The mechanism of chlorothiazide-induced carbohydrate intolerance.

In order to establish the mechanism(s) of chlorothiazide-induced hyperglycemia, measurements of blood glucose, plasma insulin, liver glycogen and hepatic cyclic adenosine 3':5'-monophosphate (cyclic AMP) levels, and liver phosphodiesterase activity were made in rats administered 10, 25, 50 or 100 mg/kg of the drug. Comparison of data obtained on these animals with those from controls revealed significant and dose-dependent increases in blood glucose, decreases in liver glycogen, increases in hepatic cyclic AMP and inhibition of phosphodiesterase. Although basal insulin levels were significantly increased at the two higher doses of chlorothiazide, ratios of blood glucose/plasma insulin levels showed suppression of insulin secretion at all four doses. However, this suppression was not dose-related. All effects of the drug were maximal at 2 hours after subcutaneous administration. The results of this investigation indicate that the primary mechanism of chlorothiazide-induced carbohydrate intolerance is cyclic AMP-mediated stimulation of glycogenolysis and inhibition of glycogenesis. Suppression of insulin secretion is secondary but probably contributes to the hyperglycemia.

Animals↗
PubMed1977

Interaction of coagulation factor Xa with human platelets.

When human 125I-labeled Factor Xa is incubated with washed platelets, prothrombin, and Ca2+, a small amount of thrombin is formed which causes the platelet release reaction after a period of time that decreases as the Xa concentration is increased from 0.9 to 19 ng/ml. After a further lag period, the Xa binds reversibly to receptors on the platelet surface and rapid thrombin formation follows (3 units or 1 mug of thrombin formed per min per ng of Xa bound to 10(8) platelets). When platelets are treated with either htrombin (0.5 units/ml) or calcium ionophore A23187 prior to addition of Xa, binding begins immediately. Thrombin formation occurs at the platelet surface at rates that correlate with the amount of Xa bound. Dibutyryl cyclic AMP inhibits the release reaction, Xa binding, and rate of thrombin generation in parallel. The platelet Xa receptor is distinct from the previously described thrombin receptor and appears to be a protein because treatment of platelets with thrombin at 50 units/ml destroys Xa binding sites. The results suggest that specific receptors for Xa appear on the platelet surface after the release reaction occurs. The bound Xa catalyzes thrombin formation 1000-fold faster than does Xa added to reactions in which phospholipids are substituted for platelets.

Blood Platelets↗