Osmotically-induced and photo-induced deformations of disk membranes

Dynamic light scattering from dilute suspensions of thin discs and thin rods as limiting forms of cylinder, ellipsoid and ellipsoidal shell of revolution

A previous formulation of the field correlation function G1(tau) of light quasielastically scattered from suspensions of rigid rods undergoing anisotropic translational as well as rotational diffusion (T. Maeda and S. Fujime, Macromolecules 17 (1984) 1157) was extended to the cases of suspensions of cylinders (length L and radius R), ellipsoids and ellipsoidal shells of revolution (x2/b2 + y2/b2 + z2/a2 = 1). The present formulation includes that for suspensions of rigid rods in the limit of KR 1 or in the limit of b/a 1 and Kb 1 (an extremely prolate ellipsoid), and also that for suspensions of discs in the limit of KL 1 or in the limit of b/a 1 and Ka 1 (an extremely oblate ellipsoid), where K is the length of the scattering vector. Explicit forms of G1(tau), of the first cumulant Gamma of G1(tau) and of the dynamic form factors will be given, and numerical methods suitable for computation of dynamic form factors will be discussed. The present results can be applied to the analysis of experimental data for dilute suspensions of thin rods and thin discs. When the situation is favorable, our method can provide transport coefficients D1, D3, and Theta from dynamic light-scattering data only, where D(1) and D(3) are, respectively, the translational diffusion coefficients parallel with the x (y) and z axes, and Theta the rotational diffusion coefficient around the x (y) axis.

Dynamic light scattering from polydisperse suspensions of thin ellipsoidal shells of revolution with submicron diameters

Osmotic swelling of membrane vesicles has been studied in combination with dynamic light scattering, to obtain information about the elastic properties of biomembranes. In such studies, there arise some technical problems specific to dynamic light scattering, which include the effects on the light-scattering results of the size distribution and nonsphericity of the vesicles with submicron sizes. Even for highly monodisperse suspensions of spherical vesicles (sigma/dn = [(the mean of d2)/d2n-1]1/2 = 0.1; dn being the number-average diameter of vesicles), the average diameter d obtained from dynamic light scattering is shown to be strongly dependent on dnK, where K is the length of the scattering vector. This is solely due to the shell structure of the vesicles. For ellipsoidal vesicles, another complication appears which is due to the rotational motion of ellipsoids.

The osmotic response of large unilamellar vesicles studied by quasielastic light scattering

Large unilamellar vesicles of two phosphatidylcholines, one saturated (DMPC) and the other unsaturated (DOPC), prepared by the reverse-phase evaporation method were studied using the quasielastic light scattering technique. The accurate sizing obtained by this technique showed an osmotic response for the two kinds of vesicles when the salinity of the external medium was diluted. The elastic moduli of lipid vesicles bilayers in the liquid phase were then estimated according to the elasticity theory of spherical shells taking into account salt leakage data known from the literature.

Dielectric behavior of polyelectrolytes. IV. Electric polarizability of rigid biopolymers in electric fields

The equilibrium Kerr effect of a system of mobile charges constrained to the surface of biomacromolecules is calculated. Cylindrical and spherical geometries are considered. For the cylinder we determine the anisotropy of electric polarizability as a function of length, temperature, and number of charged species in the low-field regime, and the fraction of the maximum induced dipole in the field direction for higher electric fields. The results are compared to experimental data for DNA oligomers taken from the literature. With spherical geometry we calculate the fractional induced dipole moment as a function of electric field strength and from this deduce the orientation function. The field dependence of the orientation function is compared to experimental data in the literature for bovine disk membrane vesicles.

Dynamic light scattering study of suspensions of purple membrane

Purple membrane from Halobacterium halobium in suspensions has been studied by quasielastic light scattering. The intensity correlation functions of polarized scattered light were measured at various K2 values (K being the magnitude of the scattering vector), and the first cumulant Gamma of the field correlation function G1(tau) was obtained by a cumulant expansion method. The apparent diffusion coefficient Gamma /K2 did not increase monotonically with K2 values and showed a distinct anomaly in an intermediate range of K. A theoretical formulation of G1(tau) for a disc and an extremely oblate ellipsoidal shell of revolution (S. Fujime and K. Kubota, Biophys. Chem. 23 (1985) 1) was applied to the analysis of the spectra, and characteristic features of experimental spectra were well reproduced. It was suggested that a strong interference effect between scattered rays on Gamma /K2 should be attributed to a slight noncircular shape of the purple membrane and that a contribution to Gamma /K2 from membrane flexibility should be taken into account. This study will provide experimental evidence of the feasibility of membrane studies by dynamic light scattering.

Isolation and characterization of two distinct fractions from the inner membrane of dormant Bacillus megaterium spores

Two distinct membrane bands were obtained after sucrose velocity gradient centrifugation of crude inner membranes from dormant Bacillus megaterium spores disrupted under conditions which minimized endogenous enzyme action. These two inner membrane fractions (termed LD and HD) contained similar amounts of total and individual phospholipid species. However, LD and HD differed significantly in phospholipid/protein ratios (4.3 and 0.47 mg/mg, respectively), equilibrium densities (1.12 and 1.18 g/cm3), NADH oxidase specific activity (less than 0.01 and 0.13 mumol/min X mg), and content of specific proteins. In contrast, crude membranes prepared in identical fashion from germinated spores gave only a single inner membrane band (termed G) on sucrose velocity gradients. G had a phospholipid/protein ratio of 0.98 mg/mg, an equilibrium density of 1.16 g/cm3, and an NADH oxidase specific activity of 2.1 mumol/min X mg. Essentially all of the proteins present in LD or HD or both were found in G, consistent with the latter membrane being derived from a mixture of LD and HD. No evidence was found suggesting that there is significant degradation of dormant spore inner membrane protein upon spore germination.

Osmotic deformation of red blood cell ghosts induced by carbohydrates

The osmotic response of bovine red blood cell ghosts to a series of sugars is studied by light scattering. The sealed and right-side-out ghosts are prepared by the procedure of Steck and Kant (Steck, T.L. and Kant, J.A. (1974) Methods Enzymol. 31, 172-180), swollen in a hypotonic phosphate-buffered saline solution and their size and shape determined by elastic and quasielastic light scattering. Different carbohydrates are then added to the suspending medium in order to examine the osmotic responses, and the osmotic deformation of ghosts is shown to be spherically symmetric. Having thus established the deformation behavior, we then rank the osmotic activity of a carbohydrate relative to a standard, i.e., raffinose. It is found that the osmotic response of the ghosts to sucrose is about the same as that to raffinose, and the response to the smaller carbohydrates simply follows the number of carbons in various sugars; glucose and fractose are about 1.7 times less effective than raffinose, and pentaerythritol and meso-erythritol are 2.3 times less effective. Glyceraldehyde, which is 3.6 times less effective than raffinose, is the least effective sugar analog among those that we have tested.

Concurrent birefringence and forward light-scattering measurements of flash-bleached rod outer segments

A microretardometer--nephelometer was constructed to measure birefringence and forward-direction light scattering concurrently in single retinal rod outer segments (ROS). The relative contributions of light-induced birefringence and light-scattering changes to observed far-red transmission changes measured normal to the cell axis were evaluated in isolated, whole, flash-bleached ROS. No light-scattering transients were found corresponding to the previously reported rapid birefringence loss associated with the metarhodopsin I lead to metarhodopsin II reaction even under conditions in which such a light-scattering change has been reported for outer-segment fragments.

Electric and optical anisotropy and their osmotically induced changes of photoreceptor disk membrane vesicles

Electro-optical characterization of the photoreceptor disk membrane vesicle is performed by examining the electric field and concentration dependence of the study-state birefringence of aqueous suspensions of the vesicles. The electric polarizability anisotropy is found to be negative and of large magnitude: alpha 1 - alpha 2 = -(1-3) X 10 cm3. The optical anisotropy is determined to be also negative but of small magnitude: g 1 - g 2 = -1 X 10(-7). The specific Kerr constant deduced from the concentration dependence of the Kerr constant is found to be very large: Ksp = 7 X 10(-4) e.s.u. Upon deforming the vesicles osmotically from the spherical shell to the disk structure, the steady-state birefringence increases by an order of magnitude which is attributed solely to the increase in optical anisotropy attending the corresponding change in the geometric eccentricity of the vesicle. A plausible birefringence mechanism based on the known structural features of the vesicles is proposed, which would account for these findings.

Application of Light Scattering to Polymers, Liquid Crystals, and Biological Systems

The applications of elastic and quasielastic light scattering techniques to polymers in dilute solution, thermotropic liquid crystals and biological membrane vesicles are presented. It is focused on how we extract specific structural features or dynamic processes of these condensed medium samples through the light scattering methods. The paper reviews the light scattering studies that were carried out at the author's laboratory in Wisconsin from 1973 until 1980.

Permeability to ions of bovine retinal disk membrane vesicles in the bleached state

The permeability of the bleached disk membrane of retinal rod outer segments to univalent and divalent ions is studied by light scattering. The membranes are isolated from frozen dark-adapted bovine retinae, swollen into spherical vesicles in a hypotonic medium and bleached in dilute suspension and their size is determined by elastic and quasi-elastic light scatterings. Various electrolytes are then added to the suspending medium in order to examine their osmotic activity relative to the vesicles deformation characteristics. By following the deformation behavior of the membrane vesicles by elastic light scattering in terms of the oblate ellipsoidal shell model, the osmotic activity of a given electrolyte is qualitatively deduced and thereby the permeability of the membrane to the electrolyte is ranked in reference to a chosen standard, i.e., sucrose. By this method, we show that the permeabilities to Na+, K+, Mg2+ and Ca2+ are all alike, and those to halides (F-, Cl-, Br-, I-), nitrate and phosphates (HPO4(2-)/H2PO4-) are similar. Acetate, however, is about 3-times more permeative, while sulfate is less permeative than the other anions by about the same factor. The viability of our method is checked with use of an ionophore, lasolocid (X-537A), by establishing partial recovery from the osmotic deformation through the suppression of the cation osmotic effect. Ion-induced aggregation and pH-dependent size and shape changes are both found to be insignificant.

Dynamic kerr effect measurements on photoreceptor disk membrane vesicles

Dynamic Kerr effect measurements were performed with dilute aqueous suspensions of monodisperse spherical vesicles (approximately 1 micron diameter), isolated from the rod outer segment of bovine retina. A large birefringence, amounting to the specific Kerr constant of 10(-3) esu, can be observed. When a sufficiently long duration pulse (1 s) is applied, the decay of birefringence can be represented by a single exponential profile, yielding a relaxation time of 100 +/- 20 ms in 1 mM imidazole buffer. This is consistent with the rotatory relaxation time of these spherical membrane vesicles. When a short duration is applied, the birefringence increases more steeply and the decay profile contains several components. The slowest (terminal) relaxation time is 86 +/- 15 ms is due to the same process as the one observed in the slow pulse case.