Interaction of lanthanum chloride with human erythrocyte membrane in relation to acetylcholinesterase activity

Lanthanum chloride (1 mM) inhibits the activity of acetylcholinesterasein vitro in the human erythrocyte membrane. Lineweaver-Burk analysis indicates that lanthanum chloride induced inhibition of acetylcholinesterase activity is competitive in nature. The Arrhenius plot shows that the transition temperature of erythrocyte membrane-bound acetylcholinesterase is significantly reduced in the presence of lanthanum chloride. These results suggest that lanthanum chloride increases the fluidity of the erythrocyte membrane and this may be a cause of inhibition of membrane-bound acetylcholinesterase activity.     

Is Butyrylcholinesterase of the Rat CNS a Membrane-Bound Enzyme?

Abstract: The study of Arrhenius plots for acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activity from the rat brain and spinal cord revealed that in contrast to AChE, which exhibited biphasic Arrhenius plots with a distinct break (transition temperature) at about 16–18°C, BuChE showed no evidence of discontinuity and a higher activation energy in the physiological range of temperature. The results indicate lack of lipid-protein interaction in the case of BuChE of the CNS tissue. It is inferred that BuChE, in contrast to AChE, is not bound in any significant way to cellular membranes of the CNS tissue.     

A spin-label study of plasma membranes of adrenal chromaffin cells

Chromaffin-cell membranes were labeled with two nitroxide spin labels, one probing the interior of the membrane and one probing the interfacial region. Both spin labels indicate that the membrane undergoes a phase transition at about 26 degrees C. An Arrhenius plot of acetylcholinesterase activity exhibits a discontinuity at 26 degrees C, consistent with the existence of a phase transition at that temperature. Acetylcholine, which stimulates chromaffin cells to secrete catecholamines, and hexamethonium, a cholinergic blocker, do not affect the rotational correlation times of the spin labels. These results argue that cholinergic stimulation does not affect the fluidity of the chromaffin-cell membrane.     

Membrane phase behavior of a psychrotrophic and mesophilic bacillus

The phase properties of membranes isolated from the psychrotrophBacillus psychrophilus and the mesophileB. megaterium were examined using wide-angle X-ray diffraction. The temperature at which the transition from liquid-crystalline to crystalline (gel) phase occurred was below −30°C for both microorganisms, regardless of the temperature at which the microbial cells were grown. Thus the membranes for both microorganisms were exclusively liquid-crystalline over the entire growth temperature range. Indeed, the membrane was completely fluid at temperatures where growth of the psychrotroph ceases, thus indicating that the phase transition temperature is not the determinant of the minimum growth temperature.     

USE OF ARRHENIUS PLOTS OF Na-K ATPase and ACETYLCHOLINESTERASE AS A TOOL FOR STUDYING CHANGES IN LIPID-PROTEIN INTERACTIONS IN NEURONAL MEMBRANES DURING BRAIN DEVELOPMENT

Abstract— The activities of Na-K ATPase and acetylcholinesterase in the rat brain cortex were measured at different postnatal ages as a function of temperature. It was found that compared to acetylcholinesterase, Na-K ATPase is more strongly affected by the rise in temperature and that this response is further enhanced with age. Arrhenius plots of the data were prepared and the apparent energies of activation were computed for each plot. It was observed that all plots were biphasic except that for Na-K ATPase of the immature (5-day-old) brain which showed no transition temperature, with an apparent energy of activation of 15.5 kcal/mol. The enzyme from the mature brain (25-day-old) showed an average transition temperature of 22.6°C, with average apparent energies of activation of 15.3 and 27.2 kcal/mol above and below the transition temperature respectively. The cortex of 1-day-old rat showed no Na-K ATPase activity. Arrhenius plots of acetylcholinesterase studied at ages 1, 5 and 25 days postnatally all showed transition temperatures which increased from an average of 16.1°C for 1-day-old to 17 and 21.5°C for 5- and 25-day-old animals respectively. The average apparent energies of activation for acetylcholinesterase below the transition temperature changed from 8.3 kcal/mole at day 1 to 8.7 and 7.2 kcal/mol at days 5 and 25, while above the transition temperature they were 4.3, 5.2 and 4.1 at days 1, 5 and 25 respectively. The results are discussed in terms of the differences and changes in the interactions of Na-K ATPase and acetylcholinesterase with membrane lipids during the postnatal phase of brain development.     

The chlorpromazine inhibition of transport ATPase and acetylcholinesterase activities in the microsomal membranes of rat in vitro and in vivo

Chlorpromazine, an antipsychotic drug, is found to inhibit Na⁺,K⁺-ATPase activity in rat brain microsomal membranes in vitro in concentration and time dependent manner but some inconsistency is observed when the effect was studied with respect to different temperatures. Various ligands and/or substrate affect the inhibition by chlorpromazine in different ways. The in vivo study with this drug shows that the activities of Na⁺,K⁺-ATPase, Ca^–2-ATPase and acetylcholinesterase in the microsomal membranes of different organs are inhibit with increases in concentration or lengths of time of treatment and then levels off.     

Molecular Dynamics Simulation of Model Lipid Membranes: Structural Effects of Impurities

Abstract

The gel to fluid phase transition or ordered to disordered phase transition observed in biological membranes are simulated by using constant energy Molecular Dynamics. The surface part of the membrane is modelled as a two-dimensional matrix formed by the head groups of the phospholipid molecules. Head molecules which are modelled as three spheres fused with three force centers, interact with each other via van der Waals and Coulomb type interactions. The -so called- impurity or foreign molecule embedded in the surface represents the protein type molecule which is present in biological membranes and control its activity. It is modelled as a pentagon having one force centers in each corner. It also interacts with the surface molecules again via van der Waals and Coulomb type interactions. The surface density is kept constant in the simulations of the systems with or without impurity. Structural and orientational changes due to impurity were observed and proved by monitoring two-dimensional order parameter. It has been shown that melting of the surface or breakage of the ordering of the surface molecules becomes easier and ordered to disordered phase transition temperature was lowered by 100 K if the impurity is present.     

Higher environmental temperature-induced change in synaptosomal acetylcholinesterase activity of brain regions

Expcsure of adult male albino rats to higher environmental temperature (HET) at 35° for 2–12 hr or at 45° for 1–2 hr increases hypothalamic synaptosomal acetylcholinesterase (AChE) activity. Synaptosomal AChE activity in cerebral cortex of rats exposed to 35° for 12 hr and in cerebral cortex and pons-medulla of rats exposed to 45° for 1–2 hr are also activated. AChE activity of synaptosomes prepared from normal rat brain regions incubated in-vitro at 39° or 41° for 0.5 hr increases significantly in cerebral cortex and hypothalamus. The activation of AChE in ponsmedulla is also observed when this brain region is incubated at 41° for 0.5 hr. Increase of (a) the duration of incubation at 41° and (b) the incubation temperature to 43° under in-vitro condition decreases the synaptosomal AChE activity. Lioneweaver-Burk plots indicate that (a) in-vivo and invitro HET-induced increases of brain regional synaptosomal AChE activity are coupled with an increase ofV _max without any change inK _m (b) very high temperature (43° under in-vitro condition) causes a decrease inV _max with an increase inK _m of AChE activity irrespective of brain regions. Arrhenius plots show that there is a decrease in transition temperature in hypothalamus of rats exposed to either 35° or 45°; whereas such a decrease in transition temperature of the pons-medulla and cerebral cortex regions are observed only after exposure to 45°. These results suggests that heat exposure increases the lipid fluidity of synaptosomal membrane depending on the brain region which may expose the catalytic site of the enzyme (AChE) and hence activate the synaptosomal membrane bound AChE activity in brain regions. Further the in-vitro higher temperature (43°C)-induced inhibition of synaptosomal AChE activity irrespective of brain regions may be the cause iof partial proteolysis/disaggregation of AChE oligomers and/or solubilization of this membrane-bound enzyme.To whom to address reprint requests:     

Different membrane-bound forms of acetylcholinesterase are present at the cell surface of hepatocytes

In the present study we have determinated the acetylcholinesterase molecular forms present in rat liver hepatocytes; we have also studied the association of acetylcholinesterase with the cell surface of the hepatocytes. Subcellular fractionation indicated that rough endoplasmic reticulum and plasma-membrane-enriched fractions contains G4 and G2 acetylcholinesterase forms bound to membranes. Hepatocytes incubated with phosphatidylinositol-specific phospholipase C released about 70% of the surface acetylcholinesterase. Sedimentation analysis showed that all the solubilized acetylcholinesterase activity comes exclusively from a G2 dimer. The G4 hydrophobic form of acetylcholinesterase accounts for the additional cell-surface activity. The existence of these two forms of acetylcholinesterase on the surface of hepatocytes was further established by analyzing the phosphatidylinositol-specific phospholipase C sensitivity of the acetylcholinesterase molecular forms present in isolated rat liver plasma membranes.     

Cholesterol affects physical properties and (Na+,K+)-ATPase in basolateral membranes of renal and intestinal epithelia from thermally acclimated rainbow trout

Previous work has shown that cholesterol levels are modulated in plasma membranes from some but not all tissues of poikilotherms over the course of temperature change. To gain a better understanding of tissue and membrane domain-specific cholesterol function during thermal adaptation we examined effects of cholesterol on membrane physical properties and (Na⁺,K⁺)-ATPase in native and cholesterol-enriched basolateral membranes from kidney and intestine of thermally acclimated trout (Oncorhynchus mykiss). Membrane order (as indicated by fluorescence depolarization studies) is increased, whereas its thermal sensitivity is decreased by elevated cholesterol levels in mem branes with relatively low endogenous amounts of cholesterol (intestinal membranes and renal membranes from cold-acclimated fish). Thermal sensitivities of membrane order in kidney are 1.5-fold higher in native compared with cholesterol-enriched basolateral membranes. For renal plasma membranes, (Na⁺,K⁺)- ATPase activity is lowest near the transition between native and surpraphysiological cholesterol levels. Endogenous cholesterol levels (relative to phospholipid contents) in intestinal basolateral membranes from cold-acclimated fish vary more than 1.5-fold; membranes with cholesterol/phospholipid molar ratios of 0.3 have activities of (Na⁺,K⁺)-ATPase that are twofold lower than native membranes having a ratio of 0.2. These results suggests that maintenance of cholesterol levels in intestinal basolateral membranes during thermal acclimation may ensure sufficient activity of (Na⁺,K⁺)-ATPase. Membrane function in kidney, with its high native cholesterol content, is less likely to be affected by temperature change. Accepted: 21 January 1997     

Immobilization of acetylcholinesterase on new modified acrylonitrile copolymer membranes

The three new dual-layer matrices (polyacrylonitrile (PAN) membranes coated with physically bound chitosan (CHI)—PANCHI-A and chemically bound chitosan—PANCHI-B and PANCHI-C) for immobilization of acetylcholinesterase (AChE) were obtained. The chemical-modified PAN membrane (PAN-NaOH + ethylenediamine (EDA)) was used as a base for the prepared dual-layer membranes. For chemical chitosan bound membrane, chitosan was tethered onto the membrane surface to form a dual-layer biomimetic membrane in the presence of glutaraldehyde (GA). The basic characteristics (amount of amino groups, hydrophilicity and transport characteristics) of the chitosan-modified membranes were investigated. The SEM analyses were shown essential morphology change in the different chitosan membranes.The relative activities and V_max of the covalently immobilized enzyme on PANCHI-B and PANCHI-C membranes were higher than that on PANCHI-A membrane and chemical-modified membrane with NaOH + EDA. K_m values for the different modified membranes are lower for the chitosan-treated membranes. The pH and temperature optimum of immobilized enzyme were determined. The bound enzymes on PANCHI-B and PANCHI-C have higher thermal and storage stability in comparison with AChE on PANCHI-A membrane and free enzyme.     

Ultrastructural distribution of cholinesterase activity in the ventral nerve cord of the earthworm Lumbricus terrestris

Summary The fine structure and distribution of cholinesterase (ChE) activity in the ventral nerve cord of the earthworm (Lumbricus terrestris) was studied, using acetyl- and butyrylthiocholine iodides as substrates and iso-OMPA, 284C51 and eserine as inhibitors to discriminate between acetylcholinesterase (AChE) and other cholinesterase (ns.ChE) activities.The earthworm ventral nerve cord exhibits intense ChE activity. Both AChE and ns.ChE were present and they had identical distribution, being located mainly in the supportive glial cells. Most neurones of the ventral nerve cord contained no histochemically demonstrable activity. The ventral giant nerve cells were observed with the electron microscope to exhibit AChE activity. The enzyme was situated in the membranes of the rough-surfaced endoplasmic reticulum and in peculiar lamellated bodies but not in the membranes of the Golgi complex.     

Action of barbiturates on activity of acetylcholinesterase from synaptosomal membranes

The acetylcholinesterase from synaptosomal membranes is inhibited by anesthetics: Nembutal, brietal, and thiopental. Nembutal and brietal decrease theK _m for acetylthiocholine, without changes inV _max. A noncompetitive type of inhibition is produced by thiopental. This anesthetic decreases Arrhenius plot discontinuity by about 4°C and increases activation energies. Nembutal and brietal do not change Arrhenius plot discontinuities, but they increase activation energies. These results suggest that barbiturates change lipid-protein interactions in synaptosomal membranes.     

Temperature dependence of the acetylcholinesterase activity in synaptic membranes of the rat brain

The temperature dependence (5-40 degrees C) of the acetylcholinesterase activity in synaptic membranes of the rat brain at different substrate concentrations was studied. At low substrate concentrations, the Arrhenius plot has two linear sections. At high concentration, there is one linear section throughout the temperature range. The addition of glycerol to incubation medium to final concentrations of 1 and 2% (w/v) increases the Michaelis constant, without affecting the maximal rate and the inhibition constant. The role of diffusion in the temperature dependence of the acetylcholinesterase activity is discussed.     

Partial characterization of the inhibitory effect of lipid peroxidation on the ouabain-insensitive Na-ATPase of rat kidney cortex plasma membranes

The present work evaluates the effect of lipid peroxidation on the ouabain-insensitive Na-ATPase of basolateral plasma membranes from rat kidney proximal tubular cells as an indirect way to study the lipid dependence of this enzyme. An inverse relationship between lipid peroxidation and Na-ATPase activity was found. This effect was due neither to a change in the optimalK _m of the system for Na⁺ nor for the substrate Mg : ATP, nor the optimal pH value of the medium. The optimal temperature value, however, was shifted toward a higher value. There was also an increase of the apparent energy of activation in the region of temperatures above the transition point (20°C) with increase in lipid peroxidation. Peroxidized membranes incubated with phosphatidylcholine from soybean restored their Na-ATPase activity. On the other hand, the Na-ATPase activity was sensitive to oleoly lysophosphatidylcholine. These results suggest that lipid peroxidation might be affecting the Na-ATPase activity through either an increase of peroxidized phospholipids, which might change the membrane fluidity of the lipid microenvironment of the ATPase molecules, or through a direct effect of lysophospholipids released during the lipid peroxidation.     

Physicochemical approaches to the alcohol-membrane interaction in brain

The effects of ethanol on physicochemical and enzymatic perturbations of neuronal membranes were examined. Using synaptic plasma membrane (SPM) isolated from cerebral cortex of Sprague-Dawley rats, a biphasic mode of action for ethanol was observed with (Na⁺+K⁺)-ATPase, but not with Ca²⁺-ATPase or acetylcholinesterase. (Na⁺+K⁺)-ATPase was found to be more sensitive to low concentration of sodium deoxycholate treatment than Ca²⁺-ATPase. A sharp transition break of (Na⁺+K⁺)-ATPase activity in response to temperature changes was found with SPM preparation. Arrhenius plots of the response also indicated that (Na⁺+K⁺)-ATPase is more sensitive to temperature changes than Ca²⁺-ATPase. The fluorescence polarization of TNS-membrane complex decreases as ethanol concentration increases, indicating an increase in membrane fluidity. However, ethanol, at low concentration (<0.3%) appears to elevate TNS fluorescence, but a hhigher concentration (3%) ethanol tends to lower the intensity of maximal emission. The results of this study indicate that ethanol may interact with the synaptic plasma membranes and elicit specific biochemical responses depending on the concentration of the alcohol used.     

The mobility of PSI and PQ molecules in <Emphasis Type="Italic">Spirulina platensis</Emphasis> cells during state transition

Monomerization and trimerization of photosystem I (PSI) in cyanobacteria are reversible to response to light switched off and on, which leads to “energy spillover” to regulate excitation of the two photosystems in balance. Considering that PSI is a trans-membrane protein embedded in thylakoid membranes, the monomerization or trimerization must involve a movement of PSI in the membranes. In this work, the mobility of PSI was demonstrated by dependence of the monomerization and trimerization on temperature for intact Spirulina platensis cells undergoing a light-to-dark or a dark-to-light transition. Based on the characteristic absorbance of monomers and trimmers, it confirms that both monomerization and trimerization are temperature-sensitive. The relative populations of the monomers and trimmers are invariable above the phase transition temperature (T _PT) while directly proportional to temperature below T _PT. On the other hand, the rate to reach the equilibrium population is proportional to temperature above T _PT but invariable below T _PT. The PSI mobility and the temperature-dependent population are contrary to those of plastoquinone (PQ) molecules because PSI is a trans-membrane protein while PQ molecules are small diffusive electron carriers in thylakoid membranes as well as their distinctive sizes and environments. The less monomerization of PSI but the invariable time constant at lower temperature below T _PT may be due to that accumulation of the reduced PQ molecules results in decrease of the stromal-side H⁺ concentration which is a driving force of PSI monomerization.     

A monomeric form of human erythrocyte membrane acetylcholinesterase

Purified detergent solubilized dimeric human erythrocyte acetylcholinesterase (6.3 S form) was converted to a stable monomeric 3.9 S species when treated with 2-mercaptoethanol and iodoacetic acid. More than 60% of the enzymatic activity were recovered after this treatment. A decreased susceptibility to reduction and alkylation was observed with purified, detergent depleted acetylcholinesterase aggregates. When erythrocyte membranes (ghosts) were subjected to the same treatment, acetylcholinesterase could subsequently be solubilized as monomeric 3.9 S form and and more than 90% of the activity were recovered. Monomeric acetylcholinesterase was less reactive towards antibodies raised against (dimeric) human erythrocyte membrane acetylcholinesterase and towards antibodies against human erythrocyte membranes. The results suggest that acetylcholinesterase is present as dimeric species in human erythrocyte membranes despite the fact that fully active monomers can be obtained.     

Imipramine and lipid phase transition in inner mitochondrial membrane

As ascertained by freeze-fracture electron microscopy, imipramine prevents lateral phase separation from taking place in inner mitochondrial membranes at sub-zero temperatures. Electron spin resonance (ESR) measurements performed on mitochondrial membranes labeled with the N-oxyl-4′,4′-dimethyloxazolidine derivative of 16-ketostearic acid, show that the spin probe motion is markedly inhibited below 0°C and that 5 mM imipramine attenuates the temperature effect. These results are explained by supposing that imipramine is able to decrease the transition temperature of the inner mitochondrial membrane lipids as it does for simple lipid systems.     

Effect of double-bonds on bimolecular films in membrane models

The effect of unsaturation (especially bys cis-bonds) is studied on bimolecular films of saturated and unsaturated alkylammonium ions and alkanols between silicate surfaces as model systems for lipid layers in membranes. Three types of structures are observed: all-trans-blocks, kink-blocks and gauche-blocks. The knowledge of the sequence of these phases and their thermal transitions provides detailed deductions about the role of double-bonds. cis-Unsaturated chains are taken up in bimolecular films as isomers with cis-trans-gauche conformation. This conformation makes the shape of the chain similar to that of kinked chains (chains with gauche-trans-gauche (—) conformation) and enables the incorporation into the film without greater sterical hindrance. The experimental results are in good agreement with X-ray measurements on biological membranes by Engelman (Engelman, D.M., J. Mol. Biol. 47, 115–117 (1970) and 58, 153–165 (1971)).Increasing the concentration of cis-chains decreases the transition temperature of the kink-blocks into gauche-blocks. The variation of the transition temperature with concentration of cis-unsaturated chains in the model system is similar to that observed for Escherichia coli membranes. It is suggested that phase changes in biomembranes are of the same nature: transition of kink-block analogues as ordered phases into gauche-block assemblies as less ordered phases.