Biomedical subjects

W MacNaughtan

Publications and source records attributed to W MacNaughtan.

3 recordsLinked to original sources

PubMed1987

Forces between proteins and model polypeptides adsorbed on mica surfaces.

The forces of interaction between proteins adsorbed onto mica have been measured as a function of the distance of separation between the two mica surfaces in aqueous solutions. The results for three proteins, myelin basic protein, concanavalin A and cytochrome c, are presented together with the results for a model basic protein, poly(L-lysine). With the exception of cytochrome c at large separations, the forces of interaction are due to charges on the protein surfaces and may be fitted closely to theoretical predictions. For cytochrome c, however, no long-range electrical repulsion is observed, indicating that the negatively charged mica surface has been neutralised by the adsorption of the positively charged protein. At short surface separations, an attraction between the protein surfaces was noted. For concanavalin A, a weak attraction was observed in the presence of calcium and manganese ions only. For poly(L-lysine) and cytochrome c the attraction can be explained simply in terms of van der Waals interactions between the proteins. However, for myelin basic protein the observed attraction was an order of magnitude larger than that predicted by van der Waals theory. We believe that this additional attraction may be due to hydrophobic interactions between the adsorbed myelin basic protein molecules.

Adsorption↗

PubMed1985

An X-ray diffraction analysis of oriented lipid multilayers containing basic proteins.

X-ray diffraction techniques have been used to study the structures of lipid bilayers containing basic proteins. Highly ordered multilayer specimens have been formed by using the Langmuir-Blodgett method in which a solid support is passed through a lipid monolayer held at constant surface pressure at an air/water interface. If the lipid monolayer contains acidic lipids then basic proteins in the aqueous subphase are transferred with the monolayer and incorporated into the multi-membrane stack. X-ray diffraction patterns have been recorded from multilayers of cerebroside sulphate and 40% (molar) cholesterol both with and without polylysine, cytochrome c and the basic protein from central nervous system myelin. Electron density profiles across the membranes have been derived at between 6 A and 12 A resolution. All of the membrane profiles have been placed on an absolute scale of electron density by the isomorphous exchange of cholesterol with a brominated cholesterol analog. The distributions and conformations of the various basic proteins incorporated within the cerebroside sulphate/cholesterol bilayer are very different. Polylysine attaches to the surface of the lipid bilayer as a fully extended chain while cytochrome c maintains its native structure and attaches to the bilayer surface with its short axis approximately perpendicular to the membrane plane. The myelin basic protein associates intimately with the lipid headgroups in the form of an extended molecule, yet its dimension perpendicular to the plane of the membrane of approx. 15 A is consistent with the considerable degree of secondary structure found in solution. In the membrane plane, the myelin basic protein extends to cover an area of about 2500 A2. There is no significant penetration of the protein into the hydrocarbon region of the bilayer or, indeed, beyond the position of the sulphate group of the cerebroside sulphate molecule.

Absorptiometry, Photon↗

PubMed1982

Effects of pressure and pressure antagonists on the growth and membrane-bound ATP-ase of Acholeplasma laidlawii B.

1. Arrhenius plots of the membrane-bound ATP-ase were constructed at pressures of 300, 600 and 900 atm. Pressure shifts the plots to higher temperatures with an increase in slope. 2. These data are partially consistent with a kinetic model in which a phase transition in the lipids associated with the ATP-ase determines the activity of the enzyme. They are also consistent with a model in which the non-linear Arrhenius plot is caused by the low temperature inactivation of the enzyme, upon which pressure acts directly. 3. Pentanol inhibits the ATP-ase without affecting the Arrhenius break temperature, and therefore does not act by affecting the phase-state of lipids associated with the enzyme. The pentanol-enzyme interaction yielded the following: delta H 46 Kcal mol-1 and delta S 114 cal mol-1 deg-1. 4. Pressure inhibits cell growth in a way which is partially offset by comparable partial pressures of helium and hydrogen. Its action probably involves the ordering of the membrane bilayer which is counteracted by the fluidising effect of the gases.

Acholeplasma laidlawii↗