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Biomedical subjects

M N Jones

Publications and source records attributed to M N Jones.

At least 91 records · Page 5Linked to original sources
PubMed1979

The permeability of bilayer lipid membranes on the incorporation of erythrocyte membrane extracts and the identification of the monosaccharide transport proteins.

1. Extracts of the human erythrocyte membrane have been prepared by five different procedures involving Triton X-100 solubilization and gel chromatography. 2. The extracts have been analysed by gel electrophoresis and incorporated asymmetrically into phosphatidylcholine-cholesterol-n-decane planar bilayers. 3. Removal of excess Triton X-100 from membrane extracts or prolonged storage facilities the proteolysis of membrane extracts with the partial or complete breakdown of band 3 polypeptides (notation of Fairbanks, G., Steck, T.L. and Wallach, D.F.H. (1971) Biochemistry 10, 2606--2616) and the appearance of an enhanced zone 4.5 and low molecular weight material. 4. Incorporation of zone 4.5 polypeptides into bilayer lipid membranes increases their permeability to D-glucose at 27 and 5 degrees C. 5. It is suggested that the components of the monosaccharide system are present in band 3 polypeptides but that they can undergo proteolysis with some retention of transport activity.

Carrier Proteins↗
PubMed1978

Electrical properties and glucose permeability of bilayer lipid membranes on incorporation of erythrocyte membrane extracts.

1. Extracts of the human erythrocyte membrane have been prepared by solubilization with Triton X-100 and analysed by electrophoresis and gel filtration techniques. 2. The extracts have been incorporated asymmetrically into lecithincholesterol-n-decane planar bilayers. 3. The electrical characteristics and glucose permeabilities of the bilayers have been measured. 4. The extracts increased the electrical conductance of the bilayers and also markedly enhanced the D-glucose permeability but not the L-glucose permeability. 5. The enhanced D-glucose permeability was inhibited by monosaccharide transport inhibitors. 6. The results support the claim that a monosachharide facititated diffusion system has been set-up in vitro which has many of the characteristics of the transport system in the human erythrocyte membrane. 7. The data indicates that the trans membrane polypeptides of band 3 of the electrophoretogram of the erythrocyte membrane proteins (notation of Fairbanks, G., Steck, T.L. and Wallach, D.F.H. (1971) Biochemistry 10, 2606-2616) are implicated in D-glucose transport, although the possibility that relatively minor component of the membrane could be responsible for glucose transport cannot be eliminated.

Cell Membrane Permeability↗
PubMed1977

A microacalorimetric study of the interaction between trypsin and sodium n-dodecyl sulphate.

1. The binding of sodium n-dodecyl sulphate to trypsin and reduced trypsin has been measured by equilibrium dialysis at pH 3.5 and 5.5. 2. At pH 3.5 trypsin specifically binds surfactant at low concentration, at higher concentrations co-operative binding occurs. 3. Reduction of trypsin destroys the specific binding sites at pH 3.5. 4. At pH 5.5 both trypsin and reduced trypsin show only co-operative binding. 5. The interaction of sodium n-dodecyl sulphate with trypsin, reduced, inhibited, and thermally denatured trypsins has been studied by microcalorimetry at 25 degrees C. 6. The microcalorimetric measurements have been used to estimate enthalpy changes (deltaHd) on unfolding of trypsin; deltaHd = 82 +/- 5 kJ-mol-1 at pH 3.5 and 128 +/- 5 kJ-mol-1 at pH 5.5. 7. The unfolding of trypsin follows a different thermochemical pathway to that of reduced trypsin.

Binding Sites↗
PubMed1977

Mechanisms of intercellular adhesion.

Investigations into cellular adhesion, both of a biochemical and biophysical nature, have not yet produced an established theory or widely accepted hypothesis to explain the mechanics of this fundamental biological process although much information concerning the structure and function of the mammalian cell surface has been gained. At the present time there is increasing evidence to suggest that cellular adhesion is mediated by specific cell surface macromolecules which are capable of forming protein-carbohydrate complexes possibly resembling those found between plant lectins and their carbohydrate substrates.

Carbohydrates↗
PubMed1976

The electrophoretic properties and aggregation of mouse lymphoma cells, chinese-hamster fibroblasts and a somatic-cell hybrid.

1. The electrophoretic mobilities of a mouse lymphoma cell, a Chinese-hamster fibroblast and a somatic-cell hybrid (also fibroblastic), produced by fusion of the hamster cell and a mouse lymphoma cell, were measured at 25 degrees C over a range of pH, concentration of Ca2+ ions and concentration of La3+ ions. 2. All the cells have pI at pH3.5. 3. Ca2+ ions decrease the mobilities and zeta potentials of the cells to zero in the range 1-100mM. 4. La3+ ions lower the mobilities and zeta potentials in the range 10 muM-1 mM, and the cells become positively charged above 1 mM. 5. The data are consistent with specific adsorption of La3+ ions on approx. 2 X 10(14) sites/m2 of cell surface with a free energy of approx. -37kJ/mol. 6. The effects of Ca2+, La3+ and ionic strength on the extent of aggregation of the cells and of neuraminidase-treated cells were studied. 7. Ca2+ ions do not markedly increase aggregation, whereas La3+ ions gave rise to extensive aggregation in the range 10 muM-1 mM, corresponding to the region of La3+ adsorption. 8. Both fibroblastic cell lines are aggregated at high ionic strength. 9. The fibroblastic cells have larger amounts of trypsin-sensitive carbohydrate than does the lymphoma cell; the possible role of this material in cellular aggregation is discussed.

Binding Sites↗
PubMed1976

The enthalpy of interaction of urea with some globular proteins.

The enthalpies of interaction of urea with five globular proteins, ribonuclease A, trypsin, beta-lacto-globulin, ovalbumin and bovine serum albumin have been measured in aqueous solution at pH 7.0, I=0.005 M and 25 degrees C over a range of urea molality m from 0-15 mmol g-1 (where a 1 molal solution contains 1 mmol g-1). For all the proteins the interaction is exothermic, and there is an appreciable heat evolution at low urea concentrations, m less than 5 mmol g-1, which increases sharply at higher urea concentrations when the proteins undergo unfolding. If account is taken of the endothermic enthalpies of unfolding of the native proteins, the enthalpies of interactions of urea per unit mass denatured protein lie in the range -45 to -75 J g-1, corresponding to an average binding enthalpy of -23 kJ mol-1 bound urea.

Binding Sites↗
PubMed1976

The interaction between Beta-lactoglobulin and sodium N-dodecyl sulphate.

1. The binding of sodium n-dodecyl sulphate to beta-lactoglobulin was studied in the pH range 3.5-7.0 by equilibrium dialysis, ultracentrifugation and microcalorimetry. 2. At low binding concentrations (less than 30 bound surfactants anions per protein molecule) the complexes formed aggregates in solution. 3. At higher binding concentrations aggregation does not occur at low ionic strength (0.01 mol/litre), but continues at high ionic strength (0.1 mol/litre). 4. At 25 degrees C the enthalpy of interaction of sodium n-dodecyl sulphate with beta-lactoglobulin can be interpreted as the sum of the enthalpies of formation of a complex with 2 bound surfactant anions, with an enthalpy change of -9.5 kJ-mol-1 of bound surfactant, and complexes containing at least 22 bound surfactant anions, with limiting enthalpies per bound surfactant anion of -12.4 kJ-mol-1 at pH 3.5 and -3.25 kJ-mol-1 at pH 5.5. 5. The binding of surfactant and the enthalpy of interaction at pH 3.5 ARE NOT SIGNIFICANTLY AFFECTED BY THE ADDITION Of 8 M-urea. 6. The data indicate that at low binding concentrations the interaction is of an ionic nature, and is accompanied by a conformational change in the protein.

Calorimetry↗