EPR Linewidth (T2) Method to Measure Oxygen Permeability of Phospholipid Bilayers and Its Use to Study the Effect of Low Ethanol Concentrations
✍ Scribed by Alex I. Smirnov; R.B. Clarkson; R.L. Belford
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 193 KB
- Volume
- 111
- Category
- Article
- ISSN
- 1064-1866
No coin nor oath required. For personal study only.
✦ Synopsis
It is well known that continuous-wave EPR spectra of nitroxide cases can be neglected (1). When the oxygen diffusion conprobes (labels) introduced into phospholipid bilayers are sensitive stant, D(O 2 ), is much larger than the diffusion constant to molecular oxygen. However, accurate determination of oxygen D(SP) of the spin probe (as is likely the case for doxylbroadening from these experiments is complicated by the complex stearic acid spin probes in the phospholipid bilayer), then shapes of EPR spectra, which are strongly influenced by anisothe frequency, v, of bimolecular encounters between oxygen tropic restricted motion of the probe molecules. An accurate and the spin probe is given by ( ) method is presented to extract the oxygen broadening from the spectra measured with and without oxygen and at the same tem-
perature. The method is based on a fast convolution algorithm with Levenberg-Marquardt optimization. This method was previously applied to EPR oximetry with nitroxides exhibiting rotational mo-where R is the collision distance, c is the collision probabiltion in the fast limit. It is shown that for several membrane spin ity, and C(O 2 ) is the oxygen concentration. If the medium probes, the oxygen broadening can be described as homogeneous; (solution or membrane) is in equilibrium with the gas phase, thus, a one-linewidth-parameter fitting model is appropriate. The then the oxygen concentration in the medium can be exmethod is applied to measure permeability profiles of model mempressed as a product of oxygen partial pressure p(O 2 ) and branes composed from 1,2-dimyristoyl-sn-glycero-3-phosphochosolubility coefficient S(O 2 ). Then Eq. [1] can be written as line above and below the main phase transition. For both membrane phases, the broadening of doxyl-and sterol-type labels is
found to be homogeneous, a finding consistent with the model of Heisenberg exchange between molecular oxygen and spin probes.
where
is the permeability coefficient
As an example, the method is applied to study the ethanol effect on local oxygen permeability of a phospholipid bilayer. It is shown of the medium.
that ethanol concentrations as low as 1% (v/v) increase oxygen
Effects of bimolecular collisions of a spin probe with permeability of the bilayer. The effect is larger at the surface of oxygen or other spin-relaxing agents can be observed in the membrane than at its center, indicating that ethanol molecules pulsed EPR experiments (usually by the saturation-recovery interact primarily within the polar head region of the bilayer. method) by comparison of the relaxation rates, 1/T 1 , mea-