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37 results on '"Petrov, Peter G."'

2. Photocontrol of Protein Conformation in a Langmuir Monolayer

Author

Cicuta, Pietro, Hopkinson, Ian, and Petrov, Peter G.

Subjects
Condensed Matter - Soft Condensed Matter, Quantitative Biology - Biomolecules
Abstract

We report a method to control the conformation of a weak polyampholyte (the protein $\beta$-casein) in Langmuir monolayers by light, even though the protein is not photosensitive. Our approach is to couple the monolayer state to a photochemical reaction excited in the liquid subphase. The conformational transition of the protein molecule is triggered through its sensitivity to a subphase bulk field (pH in this study), changing in the course of the photochemical process. Thus, reaction of photoaquation of the ferrocyanide ion, which increases the subphase pH from 7.0 to about 8.3, produces a change in the surface monolayer pressure, $\Delta\Pi$, between -0.5 and +1.5 ${\rm mN/m}$ (depending on the surface concentration), signalling a conformational switch. The approach proposed here can be used to selectively target and influence different interfacial properties by light, without embedding photosensitisers in the matrix., Comment: 5 pages, revtex4, to be published in J.Chem.Phys

Published
2001
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12. Red Blood Cell Susceptibility to Pneumolysin: CORRELATION WITH MEMBRANE BIOCHEMICAL AND PHYSICAL PROPERTIES*

Author

Bokori-Brown, Monika, Petrov, Peter G., Khafaji, Mawya A., Mughal, Muhammad K., Naylor, Claire E., Shore, Angela C., Gooding, Kim M., Casanova, Francesco, Mitchell, Tim J., Titball, Richard W., and Winlove, C. Peter

Subjects
Male, Bacterial Toxins, Erythrocyte Membrane, respiratory system, Membrane Potentials, Hemolysin Proteins, Oxidative Stress, Streptococcus pneumoniae, Bacterial Proteins, Membrane Biology, Streptolysins, Diabetes Mellitus, Humans, Female
Abstract

This study investigated the effect of the biochemical and biophysical properties of the plasma membrane as well as membrane morphology on the susceptibility of human red blood cells to the cholesterol-dependent cytolysin pneumolysin, a key virulence factor of Streptococcus pneumoniae, using single cell studies. We show a correlation between the physical properties of the membrane (bending rigidity and surface and dipole electrostatic potentials) and the susceptibility of red blood cells to pneumolysin-induced hemolysis. We demonstrate that biochemical modifications of the membrane induced by oxidative stress, lipid scrambling, and artificial cell aging modulate the cell response to the toxin. We provide evidence that the diversity of response to pneumolysin in diabetic red blood cells correlates with levels of glycated hemoglobin and that the mechanical properties of the red blood cell plasma membrane are altered in diabetes. Finally, we show that diabetic red blood cells are more resistant to pneumolysin and the related toxin perfringolysin O relative to healthy red blood cells. Taken together, these studies indicate that the diversity of cell response to pneumolysin within a population of human red blood cells is influenced by the biophysical and biochemical status of the plasma membrane and the chemical and/or oxidative stress pre-history of the cell.

Published
2016

14. Red Blood Cell Susceptibility to Pneumolysin

Author

Bokori-Brown, Monika, primary, Petrov, Peter G., additional, Khafaji, Mawya A., additional, Mughal, Muhammad K., additional, Naylor, Claire E., additional, Shore, Angela C., additional, Gooding, Kim M., additional, Casanova, Francesco, additional, Mitchell, Tim J., additional, Titball, Richard W., additional, and Winlove, C. Peter, additional

Published
2016
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32. Theory of Ferromagnetic Microswimmers.

Author

Gilbert, Andrew D., Ogrin, Feodor Y., Petrov, Peter G., and Winlove, C. Peter

Subjects
MAGNETIC fields, FERROMAGNETISM, NAVIER-Stokes equations, NUMERICAL analysis, SIMULATION methods & models
Abstract

This paper considers the dynamics of a microscale swimmer based on two magnetic beads that are elastically coupled together. A time-varying external magnetic field is imposed that has two principal effects: one is to exert a torque on the magnetic beads. The second is to change the orientation of the magnetic field dipoles in one or both beads, depending on their ferromagnetic properties. This then creates an attraction or repulsion between the two dipoles. The combination of dipole attraction/repulsion, moderated by the elastic coupling, and torque gives motions that are not generally time reversible and can lead to unidirectional swimming, that is persistent motion in one direction, in a Stokes flow regime. The equations of motion for the swimmer are set up using a Lagrangian formulation and supplemented by equations giving the dipole orientation of the magnetic fields of the beads in the external field. The equations are non-dimensionalized and key parameters determined. Numerical simulations reveal a number of regimes that are studied using simplified models and multiple scale analysis. Approximate thresholds are obtained above which the swimmer moves in a closed path and below which the orientation is `trapped' giving unidirectional motion. Three mechanisms for such trapping are isolated and discussed. [ABSTRACT FROM PUBLISHER]

Published
2011
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34. Controlled Process with Random Breakdowns and Repeat Actions

Author

Dimitrov, Boyan N. and Petrov, Peter G.

Abstract

[Dimitrov Boyan N.; Димитров Боян Н.]; [Petrov Peter G.; Петров Петър Г.], Some models minimizing the duration of the unreliable process by the help of statement copies are considered.

36. The effect of α-tocopherol on the membrane dipole potential

Author

Le Nen Davey, Sterenn, Winlove, C. Peter, and Petrov, Peter G.

Subjects
572, Membrane surface potential, Membrane microdomains, Lipid rafts, a-Tocopherol, Vitamin E, Membrane dipole potential, a-Tocopherol non-antioxidant effects, a-Tocopherol Succinate, P-glycoprotein, Multi-drug efflux pump, Saquinavir, Insulin receptor, Oxidative stress, Membrane cholesterol oxidation, 7-Ketocholesterol, Oxidised cholesterol
Abstract

α-Tocopherol has a well known antioxidant action but is also considered likely to exert significant non-antioxidant effects in cell membranes. Due to its lipophilic nature α-tocopherol inserts into biological membranes where it influences the organisation of the component lipids and may therefore influence biophysical parameters including the membrane dipole potential. The dipole potential has been demonstrated to modulate the function of several membrane associated proteins and perturbation of this physical parameter by α-tocopherol may prove to be a significant non-antioxidant mechanism underlying several of its cellular effects. This study investigates the influence of α-tocopherol, and the non-antioxidant structural analogue α-tocopherol succinate, on the membrane dipole potential employing fluorescence spectroscopy techniques with the dipole potential sensitive probe Di-8-ANEPPS. Similar techniques are utilised with the surface potential sensitive probe FPE to investigate the interaction of the charged α-tocopherol succinate molecule with membranes. α-Tocopherol and α-tocopherol succinate are shown to decrease the dipole potential of egg-phosphatidylcholine vesicles and Jurkat T-lymphocyte cell membranes. This effect is placed in the context of the significant influence of membrane cholesterol oxidation on the dipole potential. 7-ketocholesterol, an oxidised form of cholesterol, significantly influences several cellular processes and is thought to mediate these effects, in part, through its physical effects on the cell membrane. These include altering the composition, and therefore biophysical properties, of rafts; structures which are considered to support the function of a host of membrane proteins. This study attempts to correlate the effect of 7-ketocholesterol on the dipole potential of microdomains with the influence of the oxysterol on the function of two microdomains associated receptors: P-glycoprotein and the insulin receptor, assessed by determining the extent of ligand binding using flow fluorocytometry. α-Tocopherol has been suggested to inhibit the raft-mediated effects of 7-ketocholesterol and the influence of this molecule on the effect of 7-ketocholesterol on the dipole potential are investigated as a potential mechanism for this inhibition. It is hypothesized that α-tocopherols may protect against the deleterious effects of cholesterol oxidation in cell membranes by excluding 7-ketocholesterol from specific microdomains, of which rafts are a subset, acting to preserve their dipole potential and maintain the function of the proteins they support. However, where significant cholesterol oxidation has previously occured the concurrent changes in the microdomain landscape of the membrane is suggested to prevent α-tocopherol succinate from eliciting this protective effect.

Published
2011

37. Effect of geometry on steady wetting kinetics and critical velocity of film entrainment

Author

Rossen Sedev, Jordan G. Petrov, Peter G. Petrov, Petrov, Jordan G, Sedev, Rossen V, and Petrov, Peter G

Subjects
Entrainment (hydrodynamics), Chemistry, media_common.quotation_subject, Kinetics, Geometry, Surfaces and Interfaces, Dissipation, Critical ionization velocity, Asymmetry, Colloid and Surface Chemistry, Meniscus, Wetting, Physical and Theoretical Chemistry, Material properties, media_common
Abstract

The velocity dependence of receding dynamic contact, angles θ r / U for siliconized cylinders of different, radii withdrawn from a glycerol-water mixture [19] show an independence on geometry and substantial influence of the material properties of the solid surface. These data are compared with the results of Ngan and Dussan [16a,b] for advancing angles θ α / U (silicon oil displacing air), which suggest a considerable effect of geometry. A similar asymmetry of the effects of geometry and material properties on the critical velocities of liquid and air film entrainment follows from the Juxtaposition of our previous results for u cr R [19,20] with literature data on U cr A onto different solid substrates. The experimental data are interpreted on the basis of the equations of Cox-Voinov [21,22], describing the data of Ngan and Dussan quantitatively. The data for the receding meniscus can be represented quantitatively only by a combined Blake-Haynes-Voinov equation taking into account the dissipation in the three-phase contact zone and in the bulk liquid.

Published
1992

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