Role of phospholipids in transport and enzymic reactions

Activation of protein kinase in the bovine corpus luteum by phospholipid and Ca2+

A new species of protein kinase has been identified in cytosol preparations from bovine corpora lutea. Enzyme activity required the simultaneous presence of Ca2+ and phospholipid, and was also enhanced by glyceryl dioleate. Phosphatidylserine was the most effective phospholipid for stimulating histone phosphorylation. Other phospholipids capable of supporting enzymic activity were, in order of decreasing activity, phosphatidylinositol, phosphatidic acid, cardiolipin and phosphatidylglycerol. Several other phospholipids tested were ineffective. A cyclic AMP-dependent protein kinase was also present in the luteal cytosol. This enzyme activity was eliminated by protein kinase inhibitor without affecting the Ca2+- and phospholipid-stimulated activity. Lysine-rich histone (IIIS) was a much better substrate than type-IIA histone for Ca2+- and phospholipid-dependent phosphorylation. Ca2+ and phospholipid also enhanced phosphorylation of endogenous luteal cytosol protein. Calmodulin, alone or in the presence of Ca2+, was unable to increase phosphorylation. Trifluoperazine inhibited protein kinase activity stimulated by Ca2+ and phospholipid. These data suggest that a phospholipid-sensitive, Ca2+-dependent protein kinase may provide an important link between hormonally-induced changes in phospholipid metabolism and corpus-luteum function.

Phospholipid modulation of low-Km cyclic AMP phosphodiesterase activity on rat adipocyte microsomes

The ability of nine phospholipids to alter the activity of low-Km cyclic AMP phosphodiesterase was examined in microsomal fractions of rat adipocytes. The enzyme was activated by phosphatidylserine (21% at 300 microM) and phosphatidylglycerol (36% at 300 microM). The activation was concentration dependent over the range 1-1000 microM. Six other phospholipids were without effect. Phosphatidylinositol 4-phosphate inhibited the activity of the enzyme over the same range of concentrations (26% at 300 microM). Phosphatidylserine also activated a partially purified preparation of the enzyme, whereas phosphatidylinositol 4-phosphate was ineffective. The mechanism of the activation of the enzyme by phosphatidylserine and phosphatidylglycerol involved an increase in the apparent Vmax of the enzyme, while the inhibition by phosphatidylinositol 4-phosphate was associated with an increase in the Km of the enzyme for substrate. The phospholipid modulators of low-Km cyclic AMP phosphodiesterase activity did not alter the activity of high-Km cyclic AMP phosphodiesterase. The ability of phospholipids to alter the activity of low-Km cyclic AMP phosphodiesterase in native membranes suggests a possible role for phospholipids in metabolic regulation.

Lipid dynamics and protein-lipid interactions in rat colonic epithelial cell basolateral membranes

Lipid dynamics and lipid-protein interactions were examined in basolateral membranes prepared from rat proximal and distal colonic epithelial cells. The results demonstrate that: (1) these membranes have a high lipid fluidity, as assessed by steady-state fluorescence polarization studies using seven fluorescent probes; (2) lipid compositional differences exist between these membranes but their fluidity is similar; (3) fluorescence polarization studies, using diphenylhexatriene (DPH), detect a thermotropic transition at 22-23 degrees C in each membrane; (4) several membrane protein activities, including adenylate cyclase and sodium-potassium dependent adenosine triphosphatase ((Na+ + K+)-ATPase) appear to be functionally dependent on the physical state of the proximal basolateral membrane's lipid.

The chemical mediators of insulin action: possible targets for postreceptor defects

An insulin-sensitive subcellular system was developed from rat adipocytes consisting of plasma membranes and mitochondria. Direct addition of insulin, concanavalin A or anti-insulin receptor antibody to this system resulted in the production of a mediator substance from the plasma membrane that caused dephosphorylation of the alpha subunit of pyruvate dehydrogenase in the mitochondria with concomitant activation of the enzyme. The mediator activated pyruvate dehydrogenase by activating the pyruvate dehydrogenase phosphatase and not by inhibiting the pyruvate dehydrogenase kinase. This was similar to the mechanism by which insulin causes activation of the enzyme in the intact cell. The insulin-sensitive mediator material from the adipocyte plasma membrane was acid-stable with a molecular weight of 1,000 to 1,500. Our laboratory has shown that the mediator that activates pyruvate dehydrogenase was present in intact adipocytes, hepatoma cells, and IM-9 lymphocytes. Insulin altered the amount or activity of the mediator consistent with the effect of the hormone on the cell. Other laboratories have shown similar effects on skeletal muscle and liver. We have shown the mediator to mimic insulin action on the low Km cyclic adenosine monophosphate (AMP) phosphodiesterase and the (calcium++-magnesium++)-adenosine triphosphatase (Ca++-Mg++)-ATPase of adipocyte plasma membranes in addition to pyruvate dehydrogenase. Other laboratories have shown the mediator to activate glycogen synthase. A body of direct and indirect evidence exists that demonstrates that more than one mediator exists. The chemical nature of the mediator is unknown but probably represents a new family of intracellular mediators of hormone action. These mediators may have clinical relevance in postreceptor defects of obesity and type II diabetes (noninsulin-dependent diabetes mellitus).

Phospholipids and the regulation of pyruvate dehydrogenase from rat adipocyte mitochondria

Aqueous dispersions of 4 out of 9 phospholipids added individually to the mitochondrial fraction from rat adipocytes altered the activity of pyruvate dehydrogenase in a dose-dependent manner from 1 to 300 microM. Phosphatidylserine increased and phosphatidylcholine, phosphatidylinositol and phosphatidylinositol-4-phosphate decreased enzyme activity. The stimulation of pyruvate dehydrogenase induced by phosphatidylserine may be reversed to below basal activity by phosphatidylinositol-4-phosphate and to basal activity by NaF, a pyruvate dehydrogenase phosphatase inhibitor. The inhibition of pyruvate dehydrogenase induced by phosphatidylinositol-4-phosphate may be restored to basal levels by the addition of calcium. These results suggest that phosphatidylserine activates pyruvate dehydrogenase activity through activation of the phosphatase, perhaps forming a phosphatidylserine-calcium complex. The inhibition by phosphatidylinositol-4-phosphate may be mediated by disruption of the enzyme complex. The phospholipids may play a physiological role in the regulation of pyruvate dehydrogenase activity.

Interaction of filipin with junctional membrane at different stages of the junction's life history

The relationship of filipin-sterol complexes to tight and gap junctions during their formation, maturation, internalization, and degradation was studied in separate cell lines. Filipin-sterol complexes tended to be excluded from mature junctions in tight junction forming COLO 316 cells and gap junction forming SW-13 cells. Once internalized, unlabeled junctional membrane appeared to fuse with heavily labeled vesicles, presumably lysosomes. Although the absence of filipin-sterol complexes from junctional membrane does not necessarily reflect the absolute sterol content of this membrane, the fact that filipin-sterol complexes are largely excluded from these areas indicates that this membrane is different from surrounding membrane. The absence of filipin-sterol complexes also permits the visualization of 'mixing' of this specialized unlabeled membrane domain with other filipin labeled membrane systems.

Effect of phophatidylcholine and phosphatidylethanolamine enrichment on the structure and function of yeast membrane

The phospholipid composition of yeast plasma membrane was manipulated by two different methods: (i) by using two auxotrophic strains KA101 (cho1) and MC13 (Cho+) which required phospholipid bases for growth and (ii) by supplementing Saccharomyces cerevisiae (3059) cells with high concentration of choline or ethanolamine. It was possible to enrich the plasma membrane with phosphatidylcholine (PC) or phosphatidylethanolamine (PE) by both methods. The uptake of amino acids, e.g., glycine, glutamic acid, leucine, lysine methionine, phenylalanine, proline and serine, was significantly reduced in PC- or PE-enriched cells. However, the extent of reduction in transport was variable among different strains. A fluorescent probe, 1-anilino-8-naphthalene sulfonate (ANS), was used to monitor the structural changes induced by altered phospholipid composition. It was observed that the relative fluorescence intensity of bound ANS was decreased as a consequence of PC or PE enrichment. The decrease in fluorescence was probably associated with reduced number of available binding sites (n) and increased apparent dissociation constant (Kd). Furthermore, our results also suggest that a critical level of PE or PC is required for proper functioning of yeast membrane.

Dexamethasone increases the synthesis of sphingomyelin in 3T3-L1 cell membranes

An acute increase in the sphingomyelin content of a plasma membrane-enriched fraction of 3T3-L1 cells was produced by incubation of the cells with 0.1 microM dexamethasone for 4 hr. Dexamethasone also stimulated the activity of the pathway of sphingomyelin synthesis by utilizing the phosphorylcholine of phosphatidylcholine as a donor to ceramide to synthesize the phospholipid (phosphatidylcholine:ceramide cholinephosphotransferase). Dexamethasone-stimulated increase in the utilization of 14C-labeled choline of phosphatidylcholine for the synthesis of sphingomyelin was inhibited by the addition of cycloheximide to the incubation. Therefore, it appears that corticosteroid stimulation of new protein synthesis was required to produce the effect. An increase in the enzymatic pathway by 83% and of the sphingomyelin content of the plasma membrane-enriched fraction by 50% after incubation with dexamethasone for 4 hr demonstrates the rapidity with which the hormone can produce considerable remodeling of the membrane. The increase in the synthetic pathway in the plasma membrane-enriched fraction was sufficient to account for the measured increase in sphingomyelin. It appears likely that the large increase in membrane sphingomyelin could contribute significantly to the many demonstrated effects of corticosteroids upon membrane processes, including transport, receptors, and enzymatic activity.

Effect of lipid peroxidation on p-aminohippurate transport by rat kidney cortical slices

1 The effect of lipid peroxidation on p-aminohippurate transport by rat kidney slices was examined. 2 Ascorbic acid and Fe2+ promoted lipid peroxidation of rat renal cortical slices in a dose-related manner. 3 Ascorbic acid (1.0 mM) and Fe2+ (0.4 mM) increased tissue water and decreased the accumulation of p-aminohippurate. 4 The addition of N,N'-diphenyl-p-phenylenediamine (antioxidant), at a concentration of 1 x 10(-6) M, completely inhibited the peroxidation and recovered the accumulation of p-aminohippurate. 5 The apparent Km of p-aminohippurate uptake was increased by ascorbic acid and Fe2+ with no change in the apparent V. 6 These data suggest that ascorbic acid and Fe2+ can cause a significant alteration in p-aminohippurate and water transport of renal cortical slices and that these effects can be correlated with lipid peroxidation.

Synthesis of the diastereoisomers of 1,2-dipalmitoyl-sn-glycero-3-thiophosphorylethanolamine and their stereospecific hydrolysis by phospholipases A2 and C

A convenient three-step synthesis of the phosphorothioate analogue of phosphatidylethanolamine is described. The reaction pathway involves the conversion of a 1,2-diacyl-sn-glycerol to its corresponding thiophosphoric acid dichloride by using PSCl3 in the presence of a tertiary base. Treatment of the dichloride with ethanolamine results in the formation of a cyclic thiophosphoramidate which, upon acidification, undergoes P--N cleavage, giving rise to 1,2-diacyl-sn-glycero-3-thiophosphorylethanolamine. 31P NMR reveals that both diastereoisomers are present in equivalent amounts. It is not possible, however, to separate the two isomers by high-pressure liquid chromatography. 31P NMR amd high-pressure liquid chromatography are used to show that phospholipases A2 and C exhibit absolute and opposite stereoselectivity in the hydrolysis of the pair of diastereoisomers.

Prevention of damage in acute spinal cord injury by peptides and pharmacologic agents

Cats were used as models of traumatic spinal cord injury. Each experimental animal received a 500 g-cm force to the exposed dura at the level of thoracic fourth vertebra. Somatosensory evoked potentials (SEPs), carotid arterial blood pressure (BP), and abdominal aorta blood flow in the treated groups were compared with those of the control group. The three treated groups received naloxone (5 mg/kg), TRH (5 mg/kg), and a combination of methyl-prednisolone sodium succinate (MP, 35 mg/kg) and epsilon-aminocaproic acid (EACA, 350 mg/kg). The SEPs which were done only in the naloxone treated group approached "normalcy" 24-26 hours after trauma as compared with the absence of SEPs in traumatized untreated group. In all three groups, the treatment increased the blood flow in abdominal aorta significantly. Morphine sulfate increased substance P (SP) immunoreactivity in the dorsal and ventral gray matter. Naloxone not only reversed this effect, it depleted SP below the saline control level. In order to establish that lipid free radicals are responsible for damage to biological membranes, their effects were also investigated in vitro: 14C-GABA uptake by mouse cortical slices which had decreased by 33% in the presence of superoxide (. O-2) generating system, horseradish peroxidase (HRP), was reduced only by 9% when superoxide dismutase was added to the medium. The latter also protected the nerve endings from damage by (. O-2) as examined by electron microscopy. It is concluded that the agents used in this study produce their ameliorating effects by virtue of their anti-inflammatory, anti-oxidant, and membrane stabilizing properties in addition to their effect on enhancing the regional microcirculation. The release of SP by naloxone may be responsible for the increase in blood flow. The consequences of traumatic injury as depicted in Fig. 1 are discussed at length.

Effects of pressure and pressure antagonists on the growth and membrane-bound ATP-ase of Acholeplasma laidlawii B

1. Arrhenius plots of the membrane-bound ATP-ase were constructed at pressures of 300, 600 and 900 atm. Pressure shifts the plots to higher temperatures with an increase in slope. 2. These data are partially consistent with a kinetic model in which a phase transition in the lipids associated with the ATP-ase determines the activity of the enzyme. They are also consistent with a model in which the non-linear Arrhenius plot is caused by the low temperature inactivation of the enzyme, upon which pressure acts directly. 3. Pentanol inhibits the ATP-ase without affecting the Arrhenius break temperature, and therefore does not act by affecting the phase-state of lipids associated with the enzyme. The pentanol-enzyme interaction yielded the following: delta H 46 Kcal mol-1 and delta S 114 cal mol-1 deg-1. 4. Pressure inhibits cell growth in a way which is partially offset by comparable partial pressures of helium and hydrogen. Its action probably involves the ordering of the membrane bilayer which is counteracted by the fluidising effect of the gases.

Dynamic modulation of mitochondrial membrane physical properties and ATPase activity by diet lipid

A longitudinal cross-over feeding design was used to investigate the relationship of dietary lipid composition to the membrane lipid environment and activity of mitochondrial ATPase in vivo. Rats were fed a polyunsaturated fatty-acid-rich oil (soya-bean oil) for 12 days, crossed-over to a monounsaturated fatty-acid-rich oil (rapeseed oil) for the next 11 days, then returned to soya-bean oil for 11 more days. Additional rats were fed either soya-bean oil or rapeseed oil throughout. Rats fed rapeseed oil had lower rates of ATPase-catalysed ATP/[32P]Pi exchange than rats fed soya-bean oil. Arrhenius plots showed higher transition temperature (Tt) and activation energy (Ea) for rats fed rapeseed oil. Switching from soya-bean oil to rapeseed oil was dynamically followed by changes in the thermotropic and kinetic properties of the mitochondrial ATPase exchange reaction. Returning to soya-bean oil reversed these changes. The rapid and reversible modulation of Tt caused by a change of the type of fat ingested suggests that membrane physicochemical properties are not under rigid intrinsic control but are continually modified by the profile of exogenously derived fatty acids. The studies suggest that in vivo the activity of mitochondrial ATPase is in part determined by dietary lipid via its influence on the microenvironment of the enzyme. The rapidity and ready reversibility of changes observed for this subcellular-membrane-bound enzyme suggest that dietary fatty-acid balance may be an important determinant of other membrane functions in the body.

Mitochondrial-membrane polar-head-group composition is influenced by diet fat

Male Sprague-Dawley rats were fed diets containing 20% (w/w) soya-bean oil, high-erucic acid rapeseed oil or low-erucic acid rapeseed oil for 0, 12 or 23 days. The type of fat present in the diet had no effect on the total phospholipid content of heart mitochondria (micrograms/mg of protein) but did influence the phospholipid class distribution. Rats fed high-erucic acid rapeseed oil for 12 or 23 days had significantly higher mitochondrial phosphatidylcholine content than rats fed soya-bean oil. Low-erucic acid rapeseed oil resulted in elevation of cardiac mitochondrial cardiolipin content after dietary treatment for 12 days. The results demonstrate in vivo that diet is a significant determinant of the phospholipid class content of subcellular membranes.

Membrane-mediated control of hepatic beta-hydroxy-beta-methylglutaryl-coenzyme A reductase

Previously we [Sabine & James (1976) Life Sci. 18, 1185--1192] proposed that 'the activity of hepatic beta-hydroxy-beta-methylglutaryl-coenzyme A reductase is critically regulated by the fluidity of its supporting microsomal membrane'. In the present work we examined further this concept of membrane-mediated control, with respect to the specific hypothesis that such control might function as a common mechanism both for the co-ordinated regulation of other enzymes affected by cholesterol feeding and also for the subcellular integration of the several physiological factors known to influence this enzyme's activity. Contrary to earlier expectations, this hypothesis now appears not to hold. We report here that, under those conditions of short-term cholesterol feeding that affected the reductase, a variety of other microsomal enzymes did not display membrane-function interactions, i.e. neither enzymes involved in cholesterol metabolism and also affected by cholesterol feeding (cholesterol 7 alpha-hydroxylase), nor those involved in cholesterol metabolism and not affected by cholesterol feeding (hydroxymethylglutaryl-CoA hydrolase, acyl-CoA:cholesterol acyltransferase), nor those not directly involved in cholesterol metabolism at all (glucose 6-phosphatase). Furthermore, we observed no evidence for the operation of membrane-mediated control of the reductase in other situations known to influence its activity, i.e. starvation, diurnal rhythm, the very early stages of cholesterol feeding and various manipulations in vitro.

Effect of high pressure on the heat activation in vivo of trehalase in the spores of Phycomyces blakesleeanus

The effect of pressure on the heat activation in vivo of trehalase in the spores of Phycomyces blakesleeanus has been investigated in order to obtain information about the molecular mechanism of the activation. For a protein conformational change directly induced in the enzyme by the heat treatment an upward shift with about 2-6 K/1000 atm (1.013 X 10(5) kPa) is to be expected in the moderate high-pressure region. On the other hand, for a phospholipid phase transition causing the activation, a continuous upward shift with about 20 K/1000 atm is to be expected. For trehalase activation we find a continuous upward shift of the activation temperature with about 5-9 K/1000 atm. The denaturation of trehalase, which occurs at slightly higher temperatures, is influenced by pressure completely as expected for a protein conformational change. The application of high pressure during spore heat activation makes it possibe to break the dormancy of the spores without concomitant activation of trehalase.

On the mechanism of regulation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase and of acyl coenzyme A:cholesterol acyltransferase by dietary fat

The activity and the kinetic properties of hydroxymethylglutaryl-CoA reductase and of acyl-CoA:cholesterol acyltransferase in the liver microsomal fraction have been compared between rats fed on either unsaturated or on saturated fat. When rats wre fed for 12h on a compounded diet containing either safflower seed oil or tristearin the composition of the fatty acyl chains of the microsomal phospholipids was shown to be relatively more unsaturated in the rats that received the unsaturated fat. The activity of hydroxymethylglutaryl-CoA reductase in the microsomal fraction was considerably reduced in rats fed on compounded diet containing unsaturated fat whereas this dietary condition resulted in a considerable increase in the activity of acyl-CoA:cholesterol acyltransferase. Similar effects were observed after feeding rats for 12 h on a commercial diet supplemented with either safflower seed oil or with tristearin. The addition of 2% cholesterol to the fat-supplemented diets resulted in both cases in a decrease in hydroxymethylglutaryl-CoA reductase and an increse in acyl-CoA:cholesterol acyltransferase activity as compared with the corresponding values from the rats fed on the fat-supplemented diets with no cholesterol. The Arrhenius plots of hydroxymethylgutaryl-CoA reductase in the microsomal fraction from rats fed on fat-supplemented commercial diet for 12 h showed breaks in the activation energy at 29.6 degrees C for the preparations from rats fed on tristearin and 28 degrees C for those from rats fed on safflower seed oil. The activation energy of the enzyme was lower above and higher below the break for the preparations from rat fed on the unsaturated fat-supplemented diet. Similar differences were obtained from the comparison of the Arrhenius plots in the preparations from rats fed on saturated fat and those in the preparations from rats fed on unsaturated fat when the diet was compounded and given to the animals for 36 h. The addition of 2% cholesterol to the commercial diet supplemented with either saturated or unsaturated fat resulted in Arrhenius plots with a constant activation energy between 37 and 22 degrees C for the enzyme in microsomal preparations from both groups of rats. The apparent Km value for hydroxymethylglutaryl-CoA was lower for the reductase in microsomal preparations from rats fed on the unsaturated fat as compared with that for the enzyme in microsomal preparations from rats fed on saturated fat. There was also a decrease in the apparent Km value for oleic acid for the acyltransferase from rats fed on unsaturated fat as compared with that for the enzyme in the microsomal preparation from the rats fed on saturated fat. The results of the present study are consistent with higher concentration of free cholesterol in endoplasmic reticular membrane in the environment of the reductase and that of acyltransferase following the administration of dietary unsaturated fat as compared with that following the administation of saturated fat.

Intrinsic differences in the perturbing ability of alkanols in bilayer: action of phospholipase A2 on the alkanol-modified phospholipid bilayer

The kinetic parameters for the steady-state rate of hydrolysis of egg phosphatidylcholine in multilamellar vesicles by bee venom phospholipase A2 are measured in the presence of 27 alkanols and several organic solvents. In general, small nonpolar solutes like enflurane, tetrahydrofuran, benzene, chloroform and diethylether do not promote the hydrolysis of multilamellar vesicles. The rate of hydrolysis shows a biphasic dependence upon the alkanol concentration for all higher (C5-C9) alcohols examined, i.e., an optimal rate of hydrolysis is observed at a characteristic concentration for each alcohol. The alkanol to lipid mole ratio (D/L ratio) in the bilayer at the peak activating concentration of an alkanol was computed from its bilayer/water partition coefficient. The branched chain alcohols induce peak activation of hydrolysis at lower D/L ratios in the bilayer than the corresponding straight chain analogs. Similarly, the longer chain n-alkanols at peak activating concentration have a lower D/L ratio than the corresponding lower alcohols. Both the Km and Vm for phosphatidylcholine increase as a function of the chain length of the activating alcohol. These kinetic parameters also depend upon the position of the substituents on the activating alcohols. Both the D/L ratio and Vm for an alcohol are found to change with the cross-sectional area of the activating alcohol across its long axis: alcohols with a more asymmetric cross-section exhibit higher Vm and a lower D/L ratio. Such correlations of Vm and D/L ratio with the molecular parameters of the alkanols are interpreted to suggest that the accessibility of the substrate molecule in the bilayer to the phospholipase is modulated by the free space introduced by the alkanols in the bilayer. Effect of tetradecane derivatives and A2C (a membrane fluidizing agent) on the phase transition characteristics of DPPC bilayers, and their susceptibility to phospholipase A2 from bee venom and pig pancreas is also reported. These solutes cause a broadening of the transition profile and reduce the size of the cooperative unit and the enthalpy of transition. These effects depend upon the mole fraction of a solute in the bilayer; however, equal concentrations of these solutes do not induce equal response. Susceptibility of the modified bilayers to phospholipase A2 depends not only upon the structure of the solute but also upon the source of the enzyme. The data show that the activity of the membrane-bound enzyme is modulated to different extents by different solutes, and the bilayer perturbing ability of these solutes may be related to the asymmetry of their cross-sectional area and to the free space introduced by the alkanols in a bilayer.

Membrane lipids can modulate guanylate cyclase activity of rat intestinal microvillus membranes

Studies of the temperature dependence (10-40 degrees C) of guanylate cyclase in rat intestinal microbillus membranes reveal a change in energy of activation (slope of the Arrhenius plot) at 30 +/- 1 degree C. The break point temperature corresponds to the lipid thermotropic transition in these membranes previously characterized by differential scanning calorimetry (range: 23-39 degrees C; peak temperature, 31 degrees C). The break point temperature for guanylate cyclase also corresponds to that of a number of other microbillus membrane enzymes and of D-glucose transport. These activities are defined as "intrinsic" membrane activities by this operational criterion. Treatment with the nonionic detergent Lubrol WX increased the guanylate cyclase activity 4- to 8-fold and removed the discontinuity in the Arrhenius plot.

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 (less than 0.3%) appears to elevate TNS fluorescence, but at higher 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.

Molecular species composition of phosphatidylcholines during the development of the avian embryo brain

A comparative approach has been used to investigate the molecular species composition of phosphatidylcholine (PC) and its age variation throughout several developmental stages of chick and duck embryo brains. The brain PC consist of 15 major molecular species which do not undergo appreciable variation in their relative abundance either during embryonic development or between equivalent stages of maturation in the 2 avian species. In fact, a highly invariable molecular architecture of PC is shown in the developing organ. Molecular species containing saturated or monounsaturated fatty acids were dominant in all stages of development of the avian embryo brain. Among these molecular species, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine accounted for 75-80% of the total PC.

Initial membrane reaction in peptidoglycan synthesis: perturbation of lipid-phospho-N-acetylmuramyl-pentapeptide translocase interactions by n-butanol

Phospho-N-acetylmuramyl-pentapeptide translocase, the initial membrane enzyme in the biosynthesis of peptidoglycan, requires a lipid microenvironment for function. n-Butanol was reversibly intercalated into membranes to perturb the hydrophobic interactions in this microenvironment in order to define further the role of lipid. In the concentration range for maximal stimulation of enzymic activity (0.12-0.18 M), n-butanol causes a 40% decrease in the fluorescence emission of the dansylated product, undecaprenyl diphosphate-(N epsilon-dansyl)pentapeptide. Since no change in emission maximum occurs below 22 degrees C in the presence of 0.12 M n-butanol, it is concluded that intercalation of this alkanol causes an increase in fluidity. Above 22 degrees C this concentration of n-butanol causes both a decrease in the fluorescence emission and a red shift in the emission maximum. It is concluded that a polarity change as well as fluidity change occurs above 22 degrees C. n-Butanol also causes a significant change in the phase transition experienced by the dansylated lipid product. Thus, it is possible with n-alkanols, e.g. n-butanol, to perturb lipid-translocase interactions resulting in an increase in fluidity in the microenvironment of the enzyme. This change in fluidity correlates with a stimulation of enzymic activity.

Glutamic acid transport in cortical synaptosomes from essential fatty acid deficient rats

the sodium dependence of the high-affinity transport of glutamic acid in rat brain synaptosomes has been studied in animals maintained on a diet deficient in essential fatty acids (EFAD), and the results compared to similar studies with animals on a normal diet. Although the data give best fit to the same kinetic model as for control data, there are differences in the constants that describe the model. Except at low sodium concentrations, uptake is lower for the EFAD gorup. As a consequence of the differences in constants for the two groups, there are quantitative differences in the transport mechanism. The rate equation for the best fit model has been utilized to define certain functions in terms of dissociation and translocation constants, glutamate, sodium, and total carrier concentrations. These functions were calculated and utilized to compare the transport mechanism for the two groups. Although there are differences between these functions for control and EFAD animals, these differences are small and therefore of doubtful physiological significance.

The dynamics of membrane structure

The membranes of living organisms are involved in many aspects of the life, growth and development of all cells. The predominant structural elements of these membranes are lipids and proteins and the basic strucvture of these molecules has been reviewed. The physical properties of the lipid constituents particularly their behavior in aqueous systems has led to the concepts of thermotropic and lyotropic mesomorphism; the interaction between different types of lipid molecules modulate this behavior. Interaction of phospholipids in aqueous systems with cholesterol, ions and drugs have been examined in this context. In addition a variety of model lipid-protein systems have been investigated and the implications of interactions between lipids and different proteins in biological membranes has been evaluated. This leads to a detailed consideration of the way lipids and proteins ae organized in cell membranes and contains an appraisal of the evidence supporting contemporary views of membrane structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Finally the biosynthesis, turnover and modulation of the properties of interacting membrane constituents is critically reviewed and possible ways of controlling the behavior of cells and organisms by altering the structural parameters of different membranes has been considered.

Phase transition characteristics of diphosphatidyl-glycerol (cardiolipin) and stereoisomeric phosphatidyldiacylglycerol bilayers. Mono- and divalent metal ion effects

Synthesis and phase transition chaaracteristics of aqueous dispersions of the homologous (12 : 0, 14 : 0, 16 : 0) diphosphatidylglycerols (cardiolipins) and phosphatidyldiacylglycerols are reported. Electron microscopy of the negatively stained aqueous dispersions reveals a characteristic lamellar structure suggesting that these phospholipid molecules are organized as bilayers in the aqueous dispersions. The phase transition temperature (Tm) and the enthalpy of transition (delta H) increase monotonically with chain length in the cardiolipin and phosphatidyldiacylglycerol series; Tm for phosphatidyldiacylglycerol is higher than that for cardiolipin of the same chain-length. The transition temperatures for the enantiomeric sn-3,3- and sn-1,1-phosphatidyldiacylglycerol and for the diastereomeric, meso-sn-1,3-phosphatidyldiacylglycerol are approximately the same. The molar enthalpy for the transition of cardiolipin-NH+4 bilayers is approximately twice the value for the phosphatidylcholines of the same chain length, i.e., the molar enthalpy per acyl chain is approximately the same in the two systems. The transition temperatures for metal ion salts of C16-cardiolipin exhibit a biphasic dependence upon the unhydrated ionic radii, i.e., the highest Tm is observed for Ca2+-cardiolipin and decreases for the salts of ions with smaller and larger ionic radii than that of Ca2+. The lowest Tm is observed for Rb+-cardiolipin. Monovalent metal salts of cardiolipin exhibit two phase transitions. This effect may result from different conformational packing of the four acyl chains due to differences in metal-phosphate binding.

Lipid environment of gastric potassium ion-stimulated adenosine triphosphatase

The K+-stimulated ATPase associated with the purified gastric microsomal fraction can be completely inactivated by treatment with 15% (v/v) ethanol for 60s at 37 degrees C, but not at 25 degrees C. Sequential exposure of the microsomal fraction to 15% ethanol at 25 degrees C and 37 degrees C caused release of 2.5% and 2.9% of the total membrane phospholipids respectively. Restoration of the enzyme activity was achieved by sonication with phosphatidylcholine in the presence of Mg2+, K+ and ATP, which were essential for the reconstitution. Our data suggest that the phospholipids extracted by 15% ethanol at 37 degrees C are derived primarily from the immediate lipid environment of the enzyme, and ATP, together with the metal ions, helps the partially delipidated enzyme to retain the appropriate configuration for the subsequent reconstitution.

Initial membrane reaction in peptidoglycan synthesis. Interaction of lipid with phospho-N-acetylmuramyl-pentapeptide translocase

The initial membrane reaction in the biosynthesis of peptidoglycan is catalyzed by phospho-N-acetylmuramyl (MurN Ac)-pentapeptide translocase (UDP-MurNAc-Ala-gamma DGlu-Lys-DAla-DAla undecaprenyl phosphate phospho-MurNAc-pentapeptide transferase). In addition to the transfer reaction, the enzyme catalyzes the exchange of [3H]uridine monophosphate with the uridine monophosphate moiety of UDP-MurN Ac-pentapeptide. Two distinct discontinuities are observed in the slopes of the Arrhenius plots of the exchange and transfer activities at 22 and 30 degrees C for the enzyme from Staphylococcus aureus Copenhagen. Anisotropy measurements of perylene fluorescence and electron spin resonance measurements of N-oxyl-4',4'-dimethyloxazolidine derivatives of 12- and 16-ketostearic acid intercalated into membranes from this organism define the lower (T1 = 16--22 degrees C) and upper (Th = 30 degrees C) boundaries of a phase transition. These values correlate with the discontinuities observed for the activity measurements. Thus, it is proposed that the physical state of the lipid micro-environment of phospho-MurNAc-penetapeptide translocase has a significant effect on the catalytic activity of this enzyme.

Alteration of the fatty acid composition of Escherichia coli by growth in the presence of normal alcohols

The addition of normal alcohols in the series n-butanol to n-octanol to cultures of Escherichia coli ML308 grown on defined or lipid-free medium (at 17, 27, and 37 degrees C) caused an alteration in the fatty acid composition of this organism: the ratio of saturated to unsaturated fatty acids increased. Changes in the relative quantities of individual fatty acid species elicited by increasing concentrations of these alcohols were as follows: (i) myristic acid remained constant: (ii) palmitic acid increased; and (iii) the combined amount of palmitoleic plus cis-methylene hexadecanoic acids changed in a way which was reflected inversely by changes in the amount of cis-vaccenic acid. Comparable changes were not observed when cells were grown in the presence of n-nonanol and n-decanol in the concentration range tested. The changes observed upon addition of normal alcohols (n-butanol to n-octanol) paralleled, in part, the alterations in fatty acid composition observed when growth temperature was increased.

Neurotrophic control of skeletal muscle phospholipids

The phospholipid composition of rat gastrocnemius muscles was assessed one to nine days after sciatic nerve transection was performed either close to the muscle (5-8 mm from the point of entrance of the nerve into the muscle for short-stump nerve sections) or far from it (30-35 mm central to the nerve's point of entrance for long-stump nerve sections). In both instances, denervation did not cause striking changes in total phospholipid content but resulted in a selective loss of 1,2-diacyl-sn-glycero-3-phosphorylethanolamine (phosphatidyl ethanolamine, GPE). The quantity of GPE in denervated muscles was found to be significantly less than that it controls (p less than 0.01) within one day for short-stump preparations, as compared to three days for long-stump preparations. Also, direct comparison of short- and long-stump GPE values showed significant differences (p less than 0.01) at all times from the first to the fifth day following denervation, with no difference detected thereafter. These results imply that maintenance of skeletal muscle GPE involves a neurogenic influence which is independent of nerve-evoked muscle activity. This conclusion may help us understand neuromuscular diseases in which perturbation of phospholipid components has been implicated.