Temperature Dependence of Nonelectrolyte Permeation across Red Cell Membranes

The temperature dependence of permeation across human red cell membranes has been determined for a series of hydrophilic and lipophilic solutes, including urea and two methyl substituted derivatives, all the straight-chain amides from formamide through valeramide and the two isomers, isobutyramide and isovaleramide. The temperature coefficient for permeation by all the hydrophilic solutes is 12 kcal mol^-1 or less, whereas that for all the lipophilic solutes is 19 kcal mol^-1 or greater. This difference is consonant with the view that hydrophilic molecules cross the membrane by a path different from that taken by the lipophilic ones. The thermodynamic parameters associated with lipophile permeation have been studied in detail. ΔG is negative for adsorption of lipophilic amides onto an oil-water interface, whereas it is positive for transfer of the polar head from the aqueous medium to bulk lipid solvent. Application of absolute reaction rate theory makes it possible to make a clear distinction between diffusion across the water-red cell membrane interface and diffusion within the membrane. Diffusion coefficients and apparent activation enthalpies and entropies have been computed for each process. Transfer of the polar head from the solvent into the interface is characterized by ΔG^‡ = 0 kcal mol^-1 and ΔS^‡ negative, whereas both of these parameters have large positive values for diffusion within the membrane. Diffusion within the membrane is similar to what is expected for diffusion through a highly associated viscous fluid.     

Water lecithin binding in lecithin-water lamellar phases at 20°C

¹H and ³¹P continuous wave and spin-echo NMR measurements have been made on lecithin-water mixtures as a function of water content at 20 °C. An analysis of the data demonstrates the existence of two water environments, lecithin bound and free. Conclusions are presented concerning the stoichiometry and kinetics of the binding. The results indicate that six molecules of water are bound to one lecithin molecule and the lifetime of the bound water is 6·10⁻⁵±3·10⁻⁵ s.     

Water and ion permeability of a native collagen membrane

With the help of a ribonucleoprotein it is possible to precipitate collagen in a layer of fibers with a 700 Å period. As collagen is a constituent of many membrane systems in the body, it seemed interesting to investigate the permeability of ions and water through a native collagen membrane.The experiments were carried out with the help of an acryl glass apparatus, where an osmotic pressure, a hydrostatic pressure difference or both can be maintained between the two bulk phases separated by the membrane. The diffusion coefficients for NaCl and KCl were found to be comparable with those in other biological membranes (D_s = 9 · 10⁻⁷cm² · s⁻¹) whereas there is difference of more than three orders of magnitude in the hydraulic permeability (L_p = 6 cm⁴ · J⁻¹ · s⁻¹).Volume flow measurements caused by an osmotic gradient indicated that the reflection coefficient for NaCl and KCl is very small. In hydrostatic pressure experiments, the membrane shows a preferred direction for volume flows which seems to have something to do with the mode of preparation of the membrane.     

Phytohemagglutinin and transmembrane proteins in agglutinated sheep erythrocyte ghost membranes

Oriented and periodically stacked sheep erythrocyte ghost membrane specimens were prepared by agglutination of the ghosts with phytohemagglutinin M and sedimentation, and were studied by X-ray diffraction. The spatial orientation of the planes of the membranes in the diffracting stack was determined from the lamellar reflections of the periodic stacking. Equatorial diffraction at (10.5 Å)⁻¹ and a (1.5 Å)⁻¹ reflection were recorded which correlate with side-to-side packed transmembrane α-helices in the agglutinated membrane. A broad (4.6 Å)⁻¹ ring with strong equatorial accentuation and broad maxima at about (2.2 Å)⁻¹ and (1.2 Å)⁻¹ were observed which are attributed to the hydrocarbon chain arrangement in lipid phases of the agglutinated ghost membrane.     

State and Phase Transition Behaviors ofQuercus rubraSeed Axes and Cotyledonary Tissues: Relevance to the Desiccation Sensitivity and Cryopreservation of Recalcitrant Seeds

Freezing and melting transitions of cellular water in embryonic axes and cotyledonary tissues of recalcitrantQuercus rubra(red oak) seeds were compared under slow and rapid cooling conditions. The relevance of desiccation sensitivity (critical water content) and state/phase transition behaviors to cryopreservation was examined. Under a slow to intermediate cooling condition (≤10°C min⁻¹), unfrozen water content in the tissues decreased to less than the critical water content, resulting in a dehydration damage. Under a rapid cooling condition (>100°C min⁻¹) using liquid nitrogen (LN₂), freeze-induced dehydration damage could be avoided if the initial water content was >0.50 g g⁻¹dry wt. However, at water content >0.50 g g⁻¹dry wt, the vitrified cellular matrix was highly unstable upon warming at 10°C min⁻¹. These results offered a theoretical explanation on the difficulty for successful cryopreservation of recalcitrant red oak embryonic axes. A complete state/phase transition diagram for red oak axes was constructed, and a vitrification-based cryopreservation protocol that employed predehydration and rapid cooling was examined. State/phase transition behaviors of cellular water are important parameters for cryopreservation; however, vitrification alone was not sufficient for seed tissues to survive the cryopreservation condition.     

Ion Diffusion Selectivity in Lecithin-Water Lamellar Phases

The diffusion coefficients of Na⁺, Rb⁺, and cl^- were determined in lecithin-water lamellar phases at 18°C as a function of phase hydration. Diffusion was measured within the phase with no transfer between phase and bulk aqueous medium. The relative diffusion coefficients of anion and cation depended strongly on phase hydration. At low water content, the diffusion coefficient of Cl^- was greater than that of Na⁺ or Rb⁺ whereas at high water content both cations diffused faster than the anion. The change in relative diffusion coefficient occurred at 0.24 g water/g phase (24% water). The possibility that a change in conformation of the lecithin polar head occurs at a phase water content of 24% is considered. The diffusion coefficients of all three ions decreased at the water content where the relative diffusion rates inverted. Freeze fracture and polarizing microscopy studies were carried out to obtain information on phase structure. The latter study indicated that a change in long-range organization of the phase occured at 24% water. This change accounts for the decrease in the ion diffusion coefficients at this water content. The change in conformation of the choline phosphate group proposed as an explanation for the change in ion selectivity could lead to changes in long-range organization of the phase as a second order-effect.     

Synthesis of [Tl4Se16]: a novel tetranuclear Tl polyselenide

(Ph₄P)₄[Tl₄Se₁₆] was prepared hydrothermally in a sealed pyrex tube by the reaction of TlCl, K₂Se₄ and Ph₄PCl in a 1:1:1 molar ratio at 110 °C for one day. The red crystals were obtained in 50% yield. Crystals of (Ph₄P)₄[Tl₄Se₁₆]: triclinic P (No. 2), Z=1, a=12.054(9), b=19.450(10), c=11.799(6) Å, α=104.63(4), β=98.86(6), γ=101.99(6)° and V=2555(3) ų at 23 °C, 2θ_max=40.0°, μ=120.7 cm⁻¹, D_calc=2.23. The structure was solved by direct methods. Number of data collected: 5206. Number of unique data having F_o²>3σ(F_o²): 1723. Final R=0.075 and R_w=0.089. [Tl₄Se₁₆]⁴⁻ consists of four, almost already linearly arranged, tetrahedral thallium centers which are coordinated by two chelating Se₄²⁻, two bridging Se₂²⁻ and four bridging Se²⁻ ligands. [Tl₄Se₁₆]⁴⁻ sits on an inversion center and possesses a central {Tl₂Se₂}²⁺ planar core. The Tl(1)–Tl(1)′ distance in this core is 3.583(6) Å. These two thallium atoms are then each linked to two cyclic Tl(Se₄) fragments via bridging Se₂²⁻ and Se²⁻ ligands forming Tl₂Se(Se₂) five-membered rings.     

Biodegradation of Methyl red by Galactomyces geotrichum MTCC 1360

Galactomyces geotrichum MTCC 1360 can decolorize triphenylmethane, azo and reactive high exhaust textile dyes. At shaking condition this strain showed 100% decolorization of a toxic azo dye Methyl red (100 m gl⁻¹) within 1 h in deionized water at 30 °C. The degradation of Methyl red was possible through a broad pH (3–12) and temperature (5–50 °C) range. Glucose and mycelium concentration had increased the decolorization rate, but the addition of 1 gl⁻¹ molasses in deionized water made decolorization possible in only 10 min. Induction in the NADH–dichloro phenol indophenol (NADH–DCIP) reductase, Malachite green reductase, laccase and lignin peroxidase (Lip) activities were observed in the cells obtained after complete decolorization, showing that there is direct involvement in the degradation of Methyl red. The absence of N-N′-dimethyl-p-phenylenediamine (DMPD) in 5 °C, 2-aminobenzoic acid (ABA) in 50 °C and both the compounds in 30 °C sample have shown the differences in the metabolic fate of Methyl red at different temperatures. The untreated dye at 300 mg l⁻¹ concentration showed 88% germination inhibition in Sorghum bicolor, whereas it was 72% in Triticum aestivum. There was no germination inhibition for both the plants by Methyl red metabolites at 300 mg l⁻¹ concentration.

The scientific relevance of the paper

The azo dye Methyl red (100 mg l⁻¹) was decolorized by G. geotrichum MTCC 1360 within 1 h at shaking condition in deionized water. This organism could decolorize Methyl red at wide pH and temperature ranges. Decolorization time was reduced to 10 min by the addition of molasses to deionized water. There was induction in laccase and Lip, NADH–DCIP reductase and Malachite green reductase activities. The metabolic fate of Methyl red changes with temperature which can be evidenced by the formation of 2-ABA at 5 °C, N-N′-DMPD at 50 °C and both the compounds were absent at 30 °C. Phytotoxicity showed that metabolites of dye had induced shoot and root length of both the tested plants.     

Phase diagram of lipid A from Salmonella minnesota and Escherichia coli rough mutant lipopolysaccharide

We have reported here on the structural polymorphism of lipid A, the “endotoxic principle” of bacterial lipopolysaccharide. For lipid A of rough mutant lipopolysaccharide from Salmonella minnesota and Escherichia coli, the three-dimensional supramolecular structures were determined with x-ray diffraction utilizing synchrotron radiation. The investigations were performed in the water concentration range 10 to 95% by weight, at [lipid A]:[Mg²⁺] molar ratios from 1:0 to 0.1:1, and in the temperature range from 20 to 70°C. These data were correlated with measurements of the β→α phase behaviour which was monitored with differential scanning calorimetry and Fourier-transform infrared spectroscopy. We found that the transition temperature of the acyl chains ranges—in the absence of Mg²⁺—from 45°C at high to 56°C at low water content, and—at an equimolar content of Mg²⁺—from 52°C at high to 59°C at low water concentrations. In the gel phase—in which the lipid A acyl chains are more disordered than those from saturated phospholipids—cubic phases are adopted at high water content (>60%) and at high [lipid A):[Mg²⁺] molar ratios. At low water contents, lamellar states are assumed exclusively. In the liquid crystalline state of lipid A, the hexagonal H_II, state is adopted under all conditions. The structural variability of lipid A is highest at high water concentrations, and structural changes may be induced by only slight changes in temperature, water content, and Mg²⁺ concentration. Under physiological conditions, however, the lipid A assemblies exhibit a strong preference to cubic structures.     

A structural transition in egg lecithin-cholesterol bilayers at 12 °C

The thermal coefficient of expansion of egg lecithin bilayer thickness, αd₁, was measured as a function of its cholesterol content up to mole ratio lecithin/cholesterol of 1:1, and over the temperature range 0–40 °C. At all cholesterol contents αd₁ changes abruptly at approximately 12 °C indicating a structural transition at this temperature. Above 12 °C, αd₁ decreases monotonically from −2·10⁻³ for pure egg lecithin to −1·10^–3 at mole ratio 1:1. Below 12 °C αd₁ is walways higher than above 12 °C and shows a sharp, anomalously high value of −6·10⁻³ at the mole ratio 2:1. The results have been interpreted as the movement of cholesterol into the bilayer or the formation of lecithin-cholesterol “complexes” at temperatures below 12 °C. Similar studies with phosphatidylinositol containing cholesterol showed no structural transition and lysolecithin containing cholesterol behaved differently giving two lamellar phases in equilibrium.     

Studies of a serum albumin-liposome complex as a model lipoprotein membrane

Electron microscopy shows that the lipoprotein dispersions formed from the interaction of negatively charged liposomes with bovine serum albumin contain closed, vesicular, multilamellar structures. Discontinuous density gradient studies indicate that the lipoprotein suspensions are vesicles in which bovine serum albumin homogenously associate with lipid.Low angle X-ray diffraction results show that all the systems, positively and negatively charged, with and without protein, have the characteristic lamellar structure observed in biological membranes. The lamellar spacing (bilayer plus water layer) of negatively charged liposomes without bovine serum albumin is 55 Å. The same lamellar separation in the positively charged system is 108 Å. The lamellar spacing corresponding to bilayer, water, and protein for the negatively charged lipoprotein system is 93 Å while that for the positively charged lipoprotein system is 91 Å. These dimensions suggest that a layer of protein one molecule thick is incorporated between the lamellae bound to the surface of the bilayer.Wide angle X-ray diffraction results indicate no major effect of the protein on the 4.1 Å spacing, characteristic of hexagonal packing of the hydrocarbon chains.A classical light scattering technique is to used to show that the lipoprotein systems are osmotically active. The solute permeability exhibited by these lipoprotein systems follows the sequence (glucose < arabinose < malonamide < glycerol). K⁺ diffusion from negatively charged lipoprotein systems is greater than that found for positively charged lipoprotein systems.     

The acetylcholine receptor: Isolation of a brain nicotinic receptor and its preliminary characterization in lipid bilayer membranes

The technique of affinity chromatography with the curarizing neurotoxins of Naja naja venom has been employed to extract nicotinic acetylcholine receptors from the brain tissues of mouse and hog. Both carbochol and hexamethonium were used as linear or step gradients to elute the receptor and its properties were investigated in lipid bilayer membranes. Of particular interest is the observation that discrete quanta of conductance could be observed across an NaCl gradient of 1.0:0.1 M. By switching the voltage-clamp across the bilayer between a positive and negative 80 mV, the separate Na⁺ and Cl⁻ conductances of these quanta could be estimated and the following conductances of the smallest discrete quanta were observed: 3.7 · 10⁻¹¹ Ω⁻¹ (Na⁺) and 5.9 · 10⁻¹¹ Ω⁻¹ (Cl⁻) for mouse brain receptors; 3.8 · 10⁻¹¹ Ω⁻¹ (Na⁺) and 4.7 · 10⁻¹¹ Ω⁻¹ (Cl⁻) for hog brain receptors. Large aggregates of receptors appeared to activate and deactivate as multiples of a basic conductance size, although there is evidence that they may not represent the actual gating of ion channels. A “background noise” that is not within the temporal capability of the recording system is also present at an intensity that seems to parallel the number of activated receptors, and in view of recent electrophysiological evidence that the relaxation lifetime of the open channel state is of a millisecond duration, it may be that this “noise” actually represent the channel gating.     

Study of water permeability through phospholipid vesicle membranes by O NMR

Vesicle suspensions of up to 5 % egg lecithin and 2.5 % cholesterol have been found to have no effect on the NMR relaxation times of ¹⁷O from water. Addition of 1–5 mM Mn²⁺ to an equimolar vesicle suspension of egg lecithin and cholesterol permitted resolution of the free induction decay into two exponential components, a fast one arising from the external water and a slow one arising from the intravesicular fluid. From the rates of relaxation the mean life time of the water molecules within the vesicles was calculated to be 1±0.1 ms at 22°C. The size of the vesicle was estimated from electron micrographs to be about 500 Å in diameter. These data yield an equilibrium water permeability, P_w, of about 8 μs⁻¹ for the vesicle membranes. From the temperature dependence of P_w an activation energy of 12±2 kcal/mol was obtained. The longitudinal relaxation time (T₁) of water within vesicles remained the same as in pure water.     

Microvascular and biochemical compensation during ventricular hypertrophy in male rainbow trout

We investigated whether there are compensatory changes in the coronary microvasculature, cardiac lipid metabolism, and myocyte ultrastructure associated with ventricular enlargement in male rainbow trout. Epicardial tissue was sampled at different stages of sexual maturation, and we estimated arterial capillary density, intercapillary diffusion distance, and applied a diffusion model to predict PO₂ at different workloads. We also measured biochemical indices of lipid metabolism and estimated fractional volumes of mitochondria and myofibrils in myocytes. Immature fish with nonenlarged ventricles had the highest capillary length densities (1620±158 mm mm⁻³). Maturing trout with moderate ventricular hypertrophy had lower capillary length densities (1103±58 mm mm⁻³) and similar diffusion distances (13.9±0.7 μm) compared with immature fish (11.7±0.9 μm). The largest ventricles had intermediate capillary length densities (1457±288 mm mm⁻³) and diffusion distances (12.8±0.8 μm). Modelling predicted that enlarged ventricles would not become anoxic even at maximal workloads. Biochemical markers of fatty acid metabolism and aerobic capacity were unchanged with hypertrophy. Volume densities of mitochondria and myofibrils were also not influenced by cardiac growth. In summary, ventricle hypertrophy results in expansion of the coronary capillary bed and the maintenance of the epicardial capacities for fat and oxidative metabolism.     

Main features of the oxidative metabolism in gills and liver of Odontesthes nigricans Richardson (Pisces, Atherinopsidae)

The aim of this work was to study comparatively the oxidative metabolism in gills and liver of a silverside, Odontesthes nigricans, in their natural environment, the Beagle Channel. Oxidative damage to lipids was evaluated by assessing TBARS and lipid radical content, in gills and liver. Gills showed a significantly higher degree of damage than liver. The content of α-tocopherol, β-carotene and catalase activity showed significantly higher values in the liver than in the gills. The ascorbyl radical (A^•) content showed no significant differences between gills and liver. The ascorbate (AH⁻) content was 12 ± 2 and 159 ± 28 nmol/mg FW in gills and liver, respectively. Oxidative metabolism at the hydrophilic level was assessed as the ratio A^•/AH⁻. The ratio A^•/AH⁻ was significantly different between organs, (6 ± 2)10^− 5 and (5 ± 2)10^− 6, for the gills and the liver, respectively. Both, lipid radical content/α-tocopherol content and lipid radical content/β-carotene content ratios were significantly higher in gills as compared to the values recorded for the liver, suggesting an increased situation of oxidative stress condition in the lipid phase of the gills. Taken as a whole, the O. nigricans liver exhibited a better control of oxidative damage than the gills, allowing minimization of intracellular damage when exposed to environmental stressing conditions.     

Permeability of bilayer lipid membranes for superoxide (O2) radicals

Egg yolk phosphatidylcholine monolamellar liposomes (1000 Å in diameter) loaded with cytochrome c were placed into an external solution, in which superoxide radicals, O₂⁻, were generated by a xanthine-xanthine oxidase system. The penetration of the superoxide radicals across the liposomal membrane was detected by cytochrome c reduction in the inner liposome compartment. The effects of modifiers and temperature on this process were studied. The permeability of liposomal membrane for O₂⁻(P′_O2⁻ = (7.6 ± 0.3) · 10^-8 cm/s), or HO₂^• (P′_HO2⁻ = 4.9 · 10^-4 cm/s) were determined. The effect of the transmembrane electric potential (K⁺ concentration gradient, valinomycin) on the permeability of liposomal membranes for O₂⁻ were investigated. It was found that O₂⁻ can penetrate across liposomal membrane in an uncharged form. The feasibility of penetration of superoxide radicals through liposomal membrane, predominantly via anionic channels, was demonstrated by the use of an intramolecular cholesterol-amphotericin B complex.     

The diffusional water permeability in the halotolerant alga Dunaliella as measured by nuclear magnetic resonance

T₁ nuclear relaxation measurements of ¹H and ¹⁷O of water have been applied to study the kinetics of the diffusional transport of water across the cytoplasmic cell membrane of Dunaliella salina and Dunaliella bardawil. The water permeability coefficients at 25°C were found to be 1.5·10⁻³ cm/s and 1.8·10⁻³ cm/s, respectively, with an activation energy of 3.7 kcal/mol. The results indicate that the cell membrane of Dunaliella exhibits high diffusional permeability to water, similar in magnitude to that found for other cells and model membranes, and a relatively low activation energy. This regularity is in contrast to the exceptionally low glycerol permeability of the membrane (Brown, F.F., Sussman, I., Avron, M. and Degani, H. (1982) Biochim. Biophys. Acta 690, 165–173).     

The X-ray structure analysis of bis-2,2′,N,N′-bipyridyl ketone cobalt(III) nitrate dihydrate

An X-ray structural analysis of bis-2,2′,N,N′-bipyridyl ketone cobalt(III) nitrate dihydrate, CoC₂₂H₂₀N₄O₄⁺· NO₃⁻·2H₂O,M_r=559.38 g/mol, P , a=8.862(2), b=16.195(3), c=8.772(2) Å, α=103.54(2), β=95.74(3), γ=105.07°, V=1164.4(4) ų, Z=2, D_x=1.595 g/cm³, Mo Kα radiation (λ=0.71073 Å), μ=7.8 cm⁻¹ and R=0.079, revealed a Co(III) cation in a slightly distorted octahedral environment. The structure reveals that the ligand di-2-pyridyl ketone (dpk) has undergone a hydration reaction across the ketone double bond and one of the hydrate oxygen atoms coordinated to the metal forming a tridentate chelate. This new Co(dpk-hydrate)₂⁺ complex displays the least distorted geometry yet reported for either 1:1 or 1:2 (metal:ligand) complexes. A geometry optimization using the INDO model Hamiltonian as implemented in the program ZINDO was performed on the title complex with the Co³⁺ modeled as a singlet. The result of the computation corroborates the geometry of the title complex as that expected for Co³⁺.     

Pressure jump relaxation kinetics of frog skin open circuit voltage and short circuit current

The relaxation kinetics of frog skin open circuit voltage, V_oc, and short circuit current I_sc, was studied by analyzing the effects of subjecting the tissue to sudden increments of hydrostatic pressure. Both V_oc and I_sc are perturbed by the pressure jump. Changes in V_oc can be resolved into three components: a rapid decrease (phase I), a second, additional decrease with time constant 2.2 s (phase II), and finally a very slow increase found only in some preparations. The amplitudes of phases I and II are linear in the range of pressures studied (<350 atm) and have respective pressure coefficients of −1.2 · 10⁻⁴atm⁻¹ and −3.7 · 10⁻⁴atm⁻¹.Under short circuit conditions phases I and II persist. The pressure coefficients of the amplitudes of phase I and II, −4.3 · 10⁻⁴atm⁻¹ and −5.0 · 10⁻⁴atm⁻¹, respectively, are larger than those of V_oc, but the time constant of phase II, 2.2 s, is the same. The sum of the amplitudes of phases I and II is directly proportional to I_sc when it is inhibited with ouabain. It is argued that in both electrical states pressure perturbs the same transport mechanism giving rise to phases I and II of V_oc and I_sc.The magnitude of the pressure coefficients of these processes implies that they arise from chemical reactions, rather than from simple, physical solution properties. Comparison of the pressure jump kinetics with the previous spectral analysis of the electrical fluctuations of frog skin suggests a common origin for both sets of phenomena.     

Structural Polymorphisms of Rough Mutant Lipopolysaccharides Rd to Ra from Salmonella minnesota

The structural polymorphisms of rough mutant lipopolysaccharides (LPS) Rd, Rc, Rb, and Ra from Salmonella minnesota (strains R4, R7, Rz, R5, R345, and R60, respectively) were investigated as a function of temperature, water content, and Mg²⁺ concentration. The gel to liquid crystalline (B↔α) phase transition temperature (T_c) and the state of order within each phase were measured by Fourier transform infrared spectroscopy. The amount of bound water was determined by differential scanning calorimetry and the three-dimensional structures in each phase state were characterized by synchrotron radiation X-ray diffraction. The results indicate an extremely complex dependence of the structural behavior of LPS on ambient conditions. The B↔α acyl chain melting temperatures at high water contents (95-97%), T_c = 31 to 32°C for LPS Rd, 33 to 35°C for LPS Rc to Rb, and 36°C for LPS Ra, increase with decreasing water content and in the presence of Mg²⁺ cations with a concomitant broadening of the transition range. Below 30 to 50% water content, no distinct phase transitions can be observed. These effects are most pronounced for LPS with the shortest sugar chains. Below 50% water content, only lamellur structures can be observed in the temperature range 5 to 80°C, independent of the Mg²⁺ concentration. Above 50% water concentration, for large [LPS]:[Mg²⁺] molar ratios the predominant structure above T_c is nonlamellar; for smaller [LPS]:[Mg²⁺] molar ratios a superposition of lamellar and nonlamellar structures is found. For all LPS Rd to Rb at low Mg²⁺ concentrations, the phase transition is connected with a change in the three-dimensional structure from lamellar or mixed lamellar/nonlamellar to a pure nonlamellar, probably cubic structure. The tendency to form nonlamellar structures decreases with the length of the core oligosaccharide. At an equimolar ratio of [LPS] and [Mg²⁺] a multibilayered organization is observed. Some of the nonlamellar structures are cubic phases with periodicities between 12 and 16 nm. The molecular dimensions of the single endotoxin molecules in the absence and the presence of external water are estimated from the different lamellar periodicities, including those of free lipid A and deep rough mutant LPS Re. These observations are discussed with respect to the biological importance of LPS as a potent inducer of biological effects in mammals.