A method for estimating the fluidity of natural membranes from the pyrene excimer/monomer fluorescence ratio (Ie/Im) is proposed. The method makes it possible to exclude artefacts such as fluorescence quenching, aggregation, and redistribution of the probe in lipid mains with different microviscosity. It is shown that, upon variation of intramembrane pyrene concentration [pyr], the occurrence of a common crossover point in pyrene fluorescence spectra normalized to the corresponding probe concentration (isoemission or isobestic point) or, as a consequence, the linear dependence of Ie/[pyr] on Im/[pyr] can serve as a criterion of diffusion (fluidity)-controlled excimerization of pyrene. The isobestic point can be used for determining the range of working concentrations of the probe in membrane suspension. It was found from the intensity of pyrene fluorescence in the isobestic point and quenching with potassium iodide that at t < 30 degrees C, the probe is uniformly distributed throughout the membrane, and its excimerization is mainly controlled by the microviscosity of environment.

Artifacts↗

PubMedDate not supplied

[Influence of UV-light on erythrocyte membrane structure and catalytic behaviour of membrane acetylcholine esterase].

UV-light is shown to induce the structural transitions in the erythrocyte membrane described by S-shape curves in plots of the structural response versus the irradiation dose. In contrast to the free acetylcholine esterase (AChE) UV-light acts on the membrane enzyme as a mixed inhibitor (simultaneous change in Vmax and Km). The modification of the environment structure of residual enzyme is suggested to be the main reason of this phenomenon. The effect is under the control of membrane integrity and disappears after its desintegration. Membrane AChE treated ultrasonically both prior to and after irradiation is inactivated without a Km change. The data obtained show the influence of erythrocyte membrane structure on the catalytic behaviour of membrane-bound AChE.

Acetylcholinesterase↗

PubMedDate not supplied

[Accumulation of methylene blue by erythrocytes and determination of its maximum sensitivity to cell damage].

The accumulation of methylene blue in native and damaged erythrocytes treated by cetyltrimethylammonium bromide at different initial concentrations (c0) of methylene blue and different volume ratios between external solution and cells (Vs/Vc) was studied. It was shown that at low methylene blue concentrations (c0 < 200 microM), the sorption of the dye by cells made the main contribution to its accumulation. As a result, the internal concentration of methylene blue exceeded manifold its external concentration and their ratio Q was 4-6 for native and 6-9 for damaged cells. As Vs/Vc decreased and especially as c0 increased, the diffusion of methylene blue inward the cells increased concentration gradient, and Q sharply fell to 0.9-1.0. The optimal values of c0 and Vs/Vc that provide the maximum sensitivity of Q to cell damage were determined. The advantages of using Q over other parameters of methylene blue accumulation were shown.

Biological Transport↗

PubMedDate not supplied

[Letter: Change in trypsin sensitivity during structural rearrangements in biological membranes].

Explore the source record for details and available documents.

Animals↗