A proposal on the function of unsaturated fatty acids and ionic lipids: the role of potential compaction in biological membranes

Enhancing effect of albumin hydrolysate on ethanol production employing Saccharomyces sake

The enhancing effect of albumin hydrolysate on ethanol production was investigated in ethanol fermentations using Saccharomyces sake. In batchwise ethanol production, addition of supplemental albumin hydrolysate and phosphatidylcholine, or albumin hydrolysate alone, brought about a more than 60% increase in final ethanol concentration (148 or 144 g/L compared with 88 g/L with no supplementation [control] after 72 h). The effect of the supplements is believed to be due to an enhanced alcohol tolerance of cells grown in media containing the supplements. Cells grown in media containing albumin hydrolysate were enriched in phenyalanine, tyrosine, and methionine in their plasma membranes. All three amino acids were also present in considerable amounts in the albumin hydrolysate. This fact suggests that the three amino acids, which are present in albumin hydrolysate, are incorporated into the plasma membranes of cells. Under ethanol production conditions in which only one amino acid among the components of albumin hydrolysate was excluded, namely phenlalanine, tyrosine, or methionine, significant reductions in ethanol production resulted.

An ultrasonic motor model for bacterial flagellar motors

A model for the transduction of energy occurring in bacterial flagellar motors is presented. In this model, the influx of ions across the channel causes the cyclic conformational change of the channel itself, which in turn produces travelling waves in one of the subcomponents of the motor, the C ring. This wave stabilizes the cyclical movement of the channel which generates the rotating force. The estimated frequency of cyclic conformational change is between 36 kHz and 6.3 MHz, i.e. in the ultrasonic range. This phenomenon is therefore referred to as the ultrasonic micromotor of microorganisms.

Effects of fatty acids on membrane currents in the squid giant axon

The effects of fatty acids on the ionic currents of the voltage-clamped squid giant axon were investigated using intracellular and extracellular application of the test substances. Fatty acids mainly suppress the Na current but have little effect on the K current. These effects are completely reversed after washing with control solution. The concentrations required to suppress the peak inward current by 50% and Hill number were determined for each fatty acid. ED50 decreased about 1/3 for each increase of one carbon atom. The standard free energy was -3.05 kJ mole-1 for CH2. The Hill number was 1.58 for 2-decenoic acid. The suppression effect of the fatty acids depends on the number of carbon atoms in the compounds and their chemical structure. Suppression of the Na current was clearly observed when the number of carbon atoms exceeded eight. When fatty acids of the same chain length were compared, 2-decenoic acid had strong inhibitory activity, but sebacic acid had no effect at all on the Na channel. The currents were fitted to equations similar to those proposed by Hodgkin and Huxley (J. Physiol. (London) 117:500-544, 1952) and the changes in the parameters of these equations in the presence of fatty acids were calculated. The curve of the steady-state activation parameter (m infinity) for the Na current against membrane potential and the time constant of activation (tau m) were shifted 20 mV in a depolarizing direction by the application of fatty acids. The time constant for inactivation (tau h) was almost no change by application of the fatty acids.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Increasing the thermosensitivity of a mammary tumor (CA755) through dietary modification

Disruption of the integrity of tumor cellular membranes has been proposed as an initiating event in hyperthermic cell death. Thermosensitivity measured by the shift in the harmonic mean of tumor regrowth delay of CA755 mammary adenocarcinomas grown in the hind legs of male BDF1, mice increased 22% when the hosts were fed a diet enriched in polyunsaturated fatty acids. Although the diet elicited the anticipated increase in tumor membrane phospholipid polyunsaturated fatty acids, the proportion of total unsaturated fatty acids decreased and the proportion of membrane-rigidifying saturated fatty acids increased. Concomitantly, the concentrations of cholesterol and phospholipid phosphorus increased and the ratio of phosphatidylethanolamine to phosphatidylcholine decreased, presumably to counter the effect of the change in the fatty acid pattern. In host liver membranes, the diet-mediated increase in proportion of polyunsaturated fatty acids was not accompanied by an increase in the proportion of rigidifying saturated fatty acids. Instead, the homeoviscous adaptation consisted of decreases in monounsaturated fatty acids and cholesterol concentration and an increase in the phosphatidylethanolamine-phosphatidylcholine ratio. Addition of a natural inhibitor of cholesterol biosynthesis to the polyunsaturated fatty acid enriched-diet reversed the diet-mediated increase in the phosphatidylethanolamine-phosphatidylcholine ratio of host liver membranes. Tumor membrane lipids from hosts fed the combined dietary factors were characterized by the formentioned rigidifying increase in saturated fatty acids and compensatory decrease in the phosphatidylethanolamine-phosphatidylcholine ratio. The inhibitor reversed the compensatory increases in cholesterol and phospholipid phosphorus concentrations. As a consequence the thermosensitivity of tumors bearing this perturbed membrane was increased.

Preparation and characterization of monodisperse unilamellar phospholipid vesicles with selected diameters of from 300 to 600 nm

A method has been developed for making large unilamellar vesicles (LUV) with low polydispersity. The LUV, constituted of dioleoylphosphatidic acid (DOPA), 300 nm in diameter are made by a modification of the pH adjustment technique (Hauser, H. and Gains, N. (1982) Proc. Natl. Acad. Sci. USA 79, 1683-1687). This size is 10 times that (30 nm) of vesicles prepared by prolonged sonication. Vesicle size is increased stepwise by adding cholesterol (to a maximum of 40 mol% cholesterol) to form vesicles in 0.15 M KCl with up to 600 nm diameter. The vesicle size is measured by photon correlation spectroscopy, electron microscopy, and by measurement of the internal volume with cyanocobalamin while calculating the number of DOPA molecules per vesicle. Vesicles are stable for at least three weeks. Sepharose 4B column chromatography of the preparation yields a peak of fractions with the same polydispersity as the original sample and shows that 30 to 40% of the original lipid in a sample is recovered as LUV. Less than 2% of the sample forms small unilamellar vesicles (SUV) (diameter = 30 nm), which emerge from the column in a separate peak. Since the remaining lipid is not suspended in the buffer during vesicle formation, for most purposes the vesicles may be used immediately after titration so that they can be prepared in less than 40 min.

Biological optimization of hyperthermia: modification of tumor membrane lipids

The sensitivity of the solid mammary adenocarcinomas CA755 and MtGB, grown in the medial aspect of the hind legs of host mice, to local hyperthermia (43.5 +/- 0.1 degrees C for 1 hr) was increased by feeding the host mice a diet enriched in linoleic acid. The enhanced sensitivity was expressed only when the diet was fed for 15 days prior to the tumor transfer. Infusion of lidocaine into the tumor immediately before the hyperthermic exposure enhanced the thermal sensitivity of the controls but not of the linoleic acid-enriched tumors. Sensitivity was analyzed by tumor growth rates and growth delay following exposure. The fatty acid patterns revealed that the proportion of polyunsaturated fatty acids (20:4 and 22:6) decreased reciprocally with increased linoleic acid in the liver phospholipids, whereas in the tumor all polyunsaturated fatty acids increased at the expense of monounsaturated fatty acids. These studies suggest that dietary lipids affected tumor cell sensitivity to hyperthermia.

Anionic lipid headgroups as a proton-conducting pathway along the surface of membranes: a hypothesis

Evidence has been gathering from several laboratories that protons in proton-pumping membranes move along or within the bilayer rather than exchange with the bulk phase. These experiments are typically conducted on the natural membrane in vivo or in vitro or on fragments of natural membrane. Anionic lipids are present in all proton-pumping membranes. Model studies on the protonation state of the fatty acids of liposomes containing entrapped water show that the bilayers always contain mixtures of protonated and deprotonated carboxylates. Protonated fatty acids form stable acid-anion pairs with deprotonated fatty acids through unusually strong hydrogen bonds. Such acid-anion dimers have a single negative charge, which is shared by the four negative oxygens of both headgroups. The two pK values of the resulting dimer will be significantly different from the pK of the monomeric species, so that the dimer will be stable over a wide pH range. It is proposed that anionic lipid headgroups in biological membranes share protons as acid-anion dimers and that anionic lipids thus trap and conduct protons along the headgroup domain of bilayers that contain such anionic lipids. Protons pumped from the other side of the membrane may enter and move within the headgroup sheet because the protonation rate of negatively charged proton acceptors is 5 orders of magnitude faster than that of water. Protons trapped in the acidic headgroup sheet need not leave this region in order to be utilized by a responsive proton-translocating pore (a transport protein using the proton gradient). Experiments suggest the proton concentration in the headgroup domain may vary widely and the anionic lipid headgroup sheet may therefore function as a proton buffer. Due to the Gouy-Chapman-Stern layer at polyanionic surfaces, anionic lipids will also sequester protons from the bulk solution at low and moderate ionic strengths. At high ionic strength metal cations may replace protons sequestered near the headgroups, but these cations cannot substitute for protons in the "proton-conducting pathway," which is based on hydrogen bonding.

Measurements of the elasticity of monolayers consisting of lipids from nerve membranes

For measurement of viscoelastic properties of monolayer-covered interfaces a longitudinal wave is generated in the plane of the interface, using a horizontal oscillating barrier. The wave propagation depends on the values of the viscoelastic parameters of the monolayer. The technique is applied here to study the surface elasticity of layers consisting of lipids extracted from nerve membranes. It is concluded that mechanical disturbances are propagated as longitudinal waves. The possibility that longitudinal waves occur in nerve membranes and the role they might play in the transmission of information in biological membranes is discussed.