Structure Of Biological Membranes Research Articles

Differential scanning calorimetric studies of ethanol interactions with distearoylphosphatidylcholine: transition to the interdigitated phase

It is well established that ethanol and other amphipathic molecules induce the formation of a fully interdigitated gel phase in saturated like-chain phosphatidylcholines (PC's). We have previously shown that the induction of interdigitation in PC's by ethanol is dependent upon the alcohol concentration, the lipid chain length, and the temperature [Nambi, P., Rowe, E. S. & McIntosh, T. J. (1988) Biochemistry 27, 9175-9182]. In the present study, we have used high-sensitivity differential scanning calorimetry to investigate the transitions of distearoylphosphatidylcholine between the noninterdigitated and the interdigitated phases. The enthalpy of the L beta' to L beta I transition is approximately half that of the L beta' to P beta' transition which occurs in the absence of ethanol. The reversibility of these transitions has also been investigated by employing both heating and cooling scans in order to establish the most stable phases as a function of temperature and ethanol concentration. It has been demonstrated that the transition to the interdigitated phase is reversible as a function of temperature. Kinetic studies on the reverse transition (L beta I to L beta') demonstrate that this transition can be very slow, requiring weeks to reach completion. The rate depends upon temperature and ethanol concentration. The slow phase changes mean that the lipid can exist for long periods of time in a phase structure which is not the most stable state. The biological significance of this type of lipid behavior is the implication that the phase structure of biological membranes may depend not only on the most stable phase structure of the lipids present but also on the synthetic pathway or other kinetic variables.

Principles of biological membrane structure: Alteration of the physical state of one side of the membrane by modulation of the physical state of the op

Although synthetic membrane technology has been and continues to be exploited in separation processes, there is great need for a new generation of synthetic membranes with the properties of specificity and selectivity that are common to biological membranes. One means by which these properties may possibly be conferred onto synthetic membranes is by the judicious incorporation of biological molecules. However, in order to design synthetic membranes with specific biological properties and/or function(s), greater understanding of the structure and properties of biological membranes themselves is needed. Accordingly, this report briefly summarizes some concepts of biological membrane structure that need to be appreciated by those who use synthetic membranes. Further, this report illustrates one important characteristic of biological membranes that is relevant to process control utilizing synthetic membranes: transmembrane signaling mechanisms by which modulation of the physical state of one side of a membrane leads to alterations in the physical state of the opposite side of the membrane.

Purification and characterization of two rabbit lung Ca 2+-dependent phospholipid-binding proteins

Two Ca 2+-dependent phospholipid-binding proteins (PLBPs) in rabbit lung cytosolic fraction have been purified to homogeneity. The apparent molecular weights of these two proteins are 36000 and 33000. Both the 36000 and 33000 PLBPs aggregated certain negatively charged unilamellar liposomes, but not the neutral phosphatidylcholine (PC) liposomes, in the presence of Ca 2+. However, both PLBPs fused PC unilamellar liposomes to membrane acceptors. The 36000 and 33000 PLBPs had different specificities for phospholipid head groups, effects of Ca 2+ and membrane charges and amino acid compositions. Both the PLBPs aggregated the surfactant membranes (lamellar bodies or from lung lavage) and nonsurfactant membranes (microsomes or mitochondria) to a level similar to that of the synthetic acidic phospholipid vesicles, but the proteins fused [ 14C]|PC liposomes to the surfactant membranes 13- to 16-times more than to the synthetic phospholipid vesicles. The 36000 PLBP fused [ 14C]PC liposomes to microsomes or mitochondria only half that of the fusion to the surfactant; the 33000 PLBP fused [ 14C]PC liposomes to the surfactant and nonsurfactant alike. The PLBP's aggregate activity was not affected by the depletion of biological membrane proteins and the disruption of the native membrane integrity, but its fusion activity was greatly reduced. These results suggest that: (1) the 36000 and 33000 PLBPs are two different proteins; (2) the PLBPs may possess two catalytic reactions, one for the aggregation of small vesicles due to the binding of the protein to phospholipid vesicles and one for the fusion of small vesicles to acceptors; (3) the fusion activity was probably regulated by biological membrane proteins or structures; and (4) lung PLBP(s) might play a role in lung surfactant biogenesis.

The surface structure of artificial and natural membranes as studied by scanning tunneling microscopy

The surface structures of noncoated biological membranes were studied by the scanning tunneling microscopy, including the surfaces of egg PC(phosphatidylcholine) liposomes, soybean PE(phosphatidylethanolamine) nonbilayer lipid tubes and the membranes of liver ascites cells.

Electric field-induced structural rearrangements in biomembranes

Structure and function of biological membranes are vitally dependent on the electric membrane polarization; prolonged depolarization of the plasma membrane causes cell death. The natural cross-membrane electric field affecting the protein/lipid dielectrics are on the order of 100 kVcm_ t. The inhomogeneous field originating from ionic groups and adsorbed small ions are of the same order of magnitude; these fields are restricted to the interfacial compartments adjacent to the membrane surface. Externally applied electromagnetic fields which are strong enough to compete with the intrinsic membrane fields, cause structural rearrangements in the proteins and in the lipid bilayer parts[l-61. For example, electro-optic data of aqueous suspensions of purple membranes indicate that bacteriorhodopsin exhibits conformational flexibility in electric field pulses (l-30 kV cmi, l-100 ps). The electric dichroism shows two kinetically different structural transitions within the protein molecule[l]. The electrically induced rearrangements comprise a rapid (r z 1 ps), but concerted, change in the orientation of both retinal and tyrosine and/or tryptophan side chains. These angular changes of position are accompanied by changes in the local protein environment of the chromophores. A slower relaxation mode (7 x 100 p(s) involves alterations in the microenvironment of aromatic amino acid residues and is accompanied by pK-changes of at least two types of proton binding sites, leading to a sequential uptake and release of protons. Light scattering data are consisitent with the maintenance of the random distribution of the membrane discs within the short duration of the applied electric fields. The kinetics of the electro-optic signals and the steep dependence of the relaxation amplitudes on the electric field strength suggest a saturable induceddipole mechanism and a rather large reaction dipole moment 0E

Determination of fluorescent probes localization in membranes by nonradiative energy transfer

One of the new methods of studying the structure and dimensions of biological membranes is based on the Förster's nonradiative energy transfer between special molecules, the so-called ‘membrane fluorescent probes’. Further development of the approach is presented in this article. It consists of the combined use of the time-resolved and steady-state fluorescence data with subsequent computer simulation of the energy transfer in membranes. Anthracene as an energy donor, and 4- p-(dimethylamino)styryl- N-dodecylpyridinium (DSP-12) or 4-dimethylaminochalcone (DMC) as energy acceptors were bound with artificial phospholipid membrane vesicles (‘liposomes’). The synchrotron radiation was used as an impulse source for the excitation light. The steady-state fluorescence data permit the area of possible probe localization in membranes to be distinguished, while the kinetic data allow them to be narrowed significantly. There is a good agreement between the obtained localization and our present-day knowledge of lipid bilayer structure. The accuracy of the method is ca. several Angströms.

X-ray diffraction studies of lipid phase transitions in hydrated mixtures of cholesterol and diacylphosphatidylcholines and their relevance to the structure of biological membranes

Previous X-ray diffraction data on the effects of temperature on hydrated cholesterol/dimyristoylphosphatidylcholine mixtures have been confirmed and equivalent new date on cholesterol/stearolyoleoylphosphatidylcholine obtained. Molecular interpretations are discussed and related to previous studies of cholesterol/dioleoylphosphatidylcholine and of cholesterol-rich biological membranes.

Possible role of adsorbed surfactant in controlling membrane permeability and function

It is well established in the physical sciences that the adsorption of a monolayer of certain surfactants onto the surface of a synthetic membrane used for ultrafiltration can greatly modify its permeability to water and its ability to transmit small solute molecules and ions of physiological interest (1–4). In this hypothesis, it is proposed that, when indogenous surfactant is adsorbed to certain membranes in the body, it can similarly modify their permeability. Since adsorption can be a rapidly reversible process, this would provide a simple physical means of controlling the overall level of physiological activity of the membrane and, possibly, an additional means of differentiating membranes according to function. The hypothesis raises many questions concerning its applicability to the general structure of biological membranes, the nature of the surfactant, its ability to adsorb to solid surfaces and the reasons why such a coating may have been missed. There are then the questions of which membranes might benefit most and what happens if the coating is too sparse or is removed unintentionally.

23] Orienting synthetic and negative biological membranes for time-averaged and time-resolved structure determinations

Publisher Summary Knowledge of the structure of biological membranes can provide a basis for understanding their functional role at a molecular level. The detailed enzymatic steps involved in processes such as the active transport of ions across otherwise impermeable membrane bilayers, the passive gating actions of ion channels, energy transduction processes (oxidative phosphorylation), light energy ion gradient transduction, and receptor/channel regulatory processes require the knowledge of both the biochemical and biophysical properties of a membrane. The correlation of a specific biochemically characterized event with an associated structural event can help in the understanding of the way biological membranes function. Methods for ordering and orienting membranes should (1) preserve the functionality of a membrane—in particular, the enzymatic or biological processes it performs, (2) not alter the inherent structure of the membrane—in particular, the conformation of proteins, and (3) where possible, be verified by other techniques to ensure that a proper order and/or orientation has been achieved.

Changes in erythrocyte membranes in burned rabbits

Eighteen white rabbits were subjected to a 30 per cent TBSA full thickness burn. Wound infection was found 9–13 days after injury and became severe a week or so later. ATPase activities, antioxidation ability, the proteins of erythrocyte membranes, and the Na + contents of erythrocytes and serum were determined. The Ca ++-ATPase activity was elevated during the first 17 days postburn, but showed a decline at the time of severe wound infection; the Na +, K +-ATPase activity showed peaks on postburn days 2 and 6, and then fluctuated above the preburn level. The change in Mg ++-ATPase activity was similar to Na +,K +-ATPase. The erythrocyte Na + content was increased, and the level of serum Na + was decreased up to postburn day 6. Subsequently the erythrocyte Na + was reduced and the serum Na + increased up to day 17 postburn. The percentage of erythrocyte haemolysis in H 2O 2 was increased after the burn and became markedly so during wound infection, indicating that the antioxidation ability of burned rabbit erythrocytes was markedly impaired. During the period of wound infection, Coomassie blue-stained protein bands in SDS-polyacrylamide gel showed some changes in size and proportion in burned rabbits. For example, the second band was wider, the band 2 to band I ratio increased, and band 5 was smaller than before injury. These results seem to show that burn injury, especially when associated with sepsis, may affect both the structure and function of biological membranes.

Audio to microwave frequency dielectric study of the pretransition region in DPL-water systems

Abstract The phospholipid–water mixtures are used as model systems to investigate the structure and function of biological membranes. The dielectric behaviour of DPPC–water and DPPE–water systems was explored at audio (≥ 2kHz) and microwave (10 GHz) frequencies versus temperature. Particular care was devoted to the pretransition below the main gel-liquid-crystalline phase transition. A possible interpretation of the pretransition mechanism is given in terms of capillary waves.

Secretion of proteins by Bacillus subtilis 168 grown in the presence of membrane active agents (alcohols)

Sodium dodecyl sulphate-polyacrylamide gel electrophoresis was used to study the composition of proteins secreted by the Gram-positive microorganism Bacillus subtilis strain 168 when the latter was grown in the presence of primary alcohols (methanol, ethanol, 1-propanol and 1-butanol). These membrane-active agents had different effects on the pattern of proteins exported by B. subtilis. The secretion of some proteins was inhibited by the alkanols while that of others was stimulated, depending on the type of drug used. All alcohols were found to decrease the activity of extracellular enzymes such as α-amylase and serine protease without affecting significantly the activity of these enzymes when tested in vitro. The observed effects might be due to the ability of these agents to perturb the structure of biological membranes, thus interfering with the process of protein translocation through the lipid layers.

Analysis of the domain structure of membranes by fragmentation and separation in aqueous polymer two-phase systems.

This paper consists of three parts. The first describes theoretically a general strategy for fragmentation and separation of membranes which can be used in the elucidation of their structure and function. The second part describes a practical separation method, partition in liquid aqueous polymer two-phase systems, which can be used for separation of macromolecules and membrane particles of biological origin. The third part gives examples of the application of this method to membrane vesicles, and how this separation in combination with the strategy described in the first part can be used for analysis of the structure of biological membranes.

Time-resolved fluorescence depolarization techniques in model membrane systems. Effect of sterols and unsaturations.

Application of time-resolved fluorescence depolarization techniques to the study of biological membrane structure and dynamics requires selective signal monitoring of specifically located intrinsic or extrinsic fluorophores. In such systems, at least to date, the fluorescence characteristics of the naturally occurring chromophores (e.g., aromatic amino acid residues, enzymatic reactional cofactors, polyenic fatty acids and sterols, chlorophyll, and retinal) are of limited use because of low and/or reabsorbed emitted intensities, low signal-to-noise ratio (e.g., light scattering), and so on.KeywordsAcyl ChainFluorescence AnisotropyFatty Acyl ChainFluorescence DepolarizationParinaric AcidThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The effects of perfluoro- n-decanoic acid (PFDA) on rat heart β-receptors, adenylate cyclase, and fatty acid composition

Perfluoro- n-decanoic acid (PFDA) is a member of a family of surfactants with numerous industrial applications. The acute toxicity of PFDA is characterized by body wasting and delayed lethality. Recent reports have indicated that the effects of PFDA may involve an action on the structure of biological membranes which results in an alteration of function. In the present study we extend our work on the membrane actions of PFDA by examining its effects on myocardial β-adrenoceptor binding characteristics and adenylate cyclase. Following a single injection of PFDA the apparent number of β-receptor binding sites was reduced compared to pair-fed controls. This change in β-receptor binding capacity was reflected in a reduced ability of norepinephrine to activate adenylate cyclase. No alterations were observed in basal adenylate cyclase activity or in the ability of NaF or guanylyl imidodiphosphate to stimulate the enzyme. The fatty acid composition of the heart was changed by PFDA treatment. Our results suggest that the toxic effects of PFDA may be due to an alteration of the membrane lipid bilayer leading to changes in the functional activity of myocardial membranes.

Influence of retinoids on the osmotic stability of erythrocytes

Vitamin A is related to a number of most important "biologically" active natural compounds. It is necessary for the growth, development, and differentiation of tissues, the processes of photoreception and reproduction, and the maintenance of immunological status. However, the molecular mechanisms of the biological action of vitamin A (besides, perhaps, its participation in the optic process) remain uninterpreted in spite of numerous investigations. In recent years, the membranotropic aspects of the action of the vitamin have attracted still greater interest [7, 28]; the importance of these aspects is shown by the facts of the detection of retinol, retinoic acid, and other retinoids in biological membranes [17], as well as numerous data on the influence of these compounds on the structure and function of biological membranes. Thus, the influence of retinol and its analogs in vivo and in vitro on the stability of the membranes of erhthrocytes [14, !5], lysosomes [23, 26], and mitochondria [2, 3, 21], and on the stability, permeability, and other properties of model membranes [5, 25] was established. Significant differences in the membranotropie action of the structurally similar compounds were thereby found [3, I!, 23].

Novel tools for determining mechanically induced modifications of membrane structure: Electrochemical and fluorescence methods

Two methods for investigating the effects of mechanical strain on the structure of biological membranes are proposed and illustrated in the case of the erythrocytic membrane. Firstly, we show that the diffusion limiting current measured at a rotating disc electrode for a biological suspension allows one to follow the variation of the adhesion of the cells to the wall with the hydrodynamic conditions, provided that the results be interpreted in the framework of partially blocked electrodes. Secondly, we propose an entirely novel method, which consists in following in a Couette flow, the variation of the light intensity of a fluorescent probe (for instance a membrane potential probe) with the shear rate. Original results concerning the erythrocytic membrane are provided both under stationary and non-stationary conditions.

Infrared spectra of Langmuir-Blodgett chlorophyll a films resolved into normal and tangential components

The infrared spectra of Langmuir-Blodgett (LB) chlorophyll a films have been obtained by attenuated total internal reflection spectroscopy for both s- and p-polarized light (light polarized perpendicular to and parallel to the incident plane, respectively) using a Fourier transform (FT) spectrometer with KBr beam splitter. Through a Kramers-Kronig (KK) transformation of the reflectance data, followed by the necessary phase correction, the spectra have been separated into the absorption and dispersion spectra for directions both normal and tangent to the plane of the film. These display considerable anisotropy, and where band assignments have been made and straightforward interpretation is possible, the data are consistent with the Chapados and Leblanc model for the conformation of chlorophyll a in LB films. These results are the first direct spectroscopic evidence of optical anisotropy in LB chlorophyll a films and result from the first correct application of the KK transformation to resolving optical anisotropy in thin films. As the procedure is readily performed using the FT algorithm of the spectrometer, the technique shows considerable promise as a routine method for probing conformational structures in LB films and biological membranes. Even in those regions of the IR where band assignments are very difficult, resolved spectra can act as “fingerprints” for different conformational states.

Phase equilibria of membrane lipids from Acholeplasma laidlawii: importance of a single lipid forming nonlamellar phases.

A basis for the reorganization of the bilayer structure in biological membranes is the different aggregate structures formed by lipids in water. The phase equilibria of all individual lipids and several in vivo polar lipid mixtures from acyl chain modified membranes of Acholeplasma laidlawii were investigated with different NMR techniques. All dioleoyl (DO) polar lipids, except monoglucosyldiglyceride (MGDG), form lamellar liquid crystalline (L alpha) phases only. The phase diagram of DOMGDG reveals reversed cubic (III), reversed hexagonal (HII), and L alpha phases. In mixtures of DOMGDG and dioleoyldiglycosyldiglyceride (DODGDG), the formation of an III (or HII) phase is enhanced by DOMGDG and low hydration or high temperatures. For in vivo mixtures of all polar DO lipids, a transition from an L alpha to an III phase is promoted by low hydration or high temperatures (50 degrees C). The phospholipids are incorporated in this III phase. Likewise, III and HII phases are formed at similar temperatures in a series of in vivo mixtures with different extents of acyl chain unsaturation. However, their melting temperatures (Tm) vary in an expected manner. All cubic and hexagonal phases, except the III phase with DOMGDG, exist in equilibrium with excess water. The maximum hydration of MGDG and DGDG is similar and increases with acyl chain unsaturation but is substantially lower than that for, e.g., phosphatidylcholine. The translational diffusion of the lipids in the cubic phases is rapid, implying bicontinuous structures. However, their appearances in freeze-fracture electron microscope pictures are different. The III phase of DOMGDG belongs to the Ia3d space group.(ABSTRACT TRUNCATED AT 250 WORDS)

Consequences of hydrophobic association in photoreactions: photodimerization of stilbenes in water

Hydrophobic interactions are of considerable importance in maintaining the structure of biological membranes, Proteins, and nucleic acids. The same interaction is also responsible for the association of organic solutes in water, a well-substantiated phenomenon.l Such an association could play a significant role during cycloaddition reactions.