Observation of Lateral Diffusion in Biomembranes by Excitation Transfer ³¹P NMR:  Estimation of Vesicle Size Distributions

Abstract

An excitation transfer 31 P NMR experiment is described which directly measures translationally induced rotation of lipid molecules in large membrane vesicles. The experiment involves selective excitation of a small subset of the lipid molecules whose axially symmetric chemical shift tensors are oriented at approximately 90°to the magnetic field. Line shapes due only to the selected molecules are then recorded as a function of the mixing time. The spectra directly reflect the time dependent orientational distribution of lipid molecules and may be analyzed in terms of the distribution of effective rotational diffusion constants, related analytically to the distribution of vesicle radii. Employing this 31 P NMR method, size distributions have been evaluated for multilamellar vesicles of dimyristoylphosphatidylcholine (DMPC) and DMPC/1.12% (mol/mol) bovine rhodopsin. In both cases the radius distributions are extremely broad, spanning more than 2 orders of magnitude in the case of the pure DMPC vesicles.

Shear-Induced States of Orientation of the Lamellar Phase of C12E4/Water

“…If the domain size is small such that diffusion of water between domains of different orientation takes place during the measurement, the value of δ is affected and an additional decrease or even a vanishing of the splitting is observed. A similar effect on the NMR line shape ,− is found when the membranes forming the lamellar phase have a strong curvature, as in vesicles, so that the diffusive motion of the water molecules along the membranes has a rotatory component.…”

Transverse Nuclear Spin Relaxation Studies of Viscoelastic Properties of Membrane Vesicles. I. Theory

“…It must be emphasized that such an approximation holds if (i) the angular amplitudes of the fluctuations are small ( n z ‘ ( r⃗ p ) ≃ 1 and n x ‘ ( r⃗ p ), n y ‘ ( r⃗ p ) ≃ 0) and if (ii) only noncanonical geometries are considered (i.e., θ B ≠ 0°, 90°). Notice that we implicitly neglect the effects of translational diffusion of the lipid molecule across the vesicle's surface; , otherwise, the probe position, r⃗ p , has to be included among the stochastic variables. Consequently, in the following, θ B is considered to be a fixed parameter.…”

Measurement of the Lateral Diffusion of Dipalmitoylphosphatidylcholine Adsorbed on Silica Beads in the Absence and Presence of Melittin: A 31P Two-Dimensional Exchange Solid-State NMR Study

“…Based on 31 P lineshape analysis, Cullis (1976) measured a value of 2.6 ϫ 10 Ϫ8 cm 2 /s for the diffusion of DPPC in small unilamellar vesicles, and a constant of 30 ϫ 10 Ϫ8 cm 2 /s was determined by 31 P two-dimensional exchange NMR of multilamellar vesicles . This two-dimensional method requires the knowledge of the vesicle radius, but the use of multilamellar vesicles always leads to a great approximation of this radius that can be spread up to two orders of magnitude around an average value (Heaton et al, 1996). The radius of the multilamellar vesicles will also depend greatly on the method of sample preparation.…”

“…Therefore, many techniques have been used, since the elaboration of the fluid mosaic model, to precisely determine the lateral diffusion constant (Vaz et al, 1984;Tocanne et al, 1989). Among the most widely used techniques is fluorescence recovery after photobleaching (FRAP) (Tocanne et al, 1989), quasielastic neutron scattering (QENS) (Köchy and Bayerl, 1993), and NMR spectroscopy Heaton et al, 1996;Lindblom and Orädd, 1996;Karakatsanis and Bayerl, 1996).…”

“…However, in all cases, it was a rough approximation, because of the radius polydispersity and the multilamellar nature of the model membrane used. Heaton et al (1996) have recently shown by 31 P NMR that in a lipid dispersion, the radius distribution is extremely broad, spanning more than two orders of magnitude in the case of pure DMPC, and therefore questioned the accuracy of the above finding. As a consequence, the determination of the lateral diffusion of lipids by 2D NMR relies on the control of the radius of the lipid vesicles.…”