Showing papers on "Membrane lipids published in 1987"

Water movement through lipid bilayers, pores, and plasma membranes

Abstract: THEORY: Osmotic Equilibrium Osmotic Transport (Osmosis) Induced by an Impermeant Solute Tracer Diffusion of Water Single-file Transport Osmotic Transport (Osmosis) LIPID BILAYER MEMBRANES: The Unmodified Membrane Nystatin an Amphotericin B. Gramicidin A PLASMA MEMBRANES: General Considerations The Red Cell Membrane Epithelia: Antidiuretic Hormone (ADH)-Induced Water Permeability Index.

Sorting of sphingolipids in epithelial (Madin-Darby canine kidney) cells.

Abstract: To study the intracellular transport of newly synthesized sphingolipids in epithelial cells we have used a fluorescent ceramide analog, N-6[7-nitro-2,1,3-benzoxadiazol-4-yl] aminocaproyl sphingosine (C6-NBD-ceramide; Lipsky, N. G., and R. E. Pagano, 1983, Proc. Natl. Acad. Sci. USA, 80:2608-2612) as a probe. This ceramide was readily taken up by filter-grown Madin-Darby canine kidney (MDCK) cells from liposomes at 0 degrees C. After penetration into the cell, the fluorescent probe accumulated in the Golgi area at temperatures between 0 and 20 degrees C. Chemical analysis showed that C6-NBD-ceramide was being converted into C6-NBD-sphingomyelin and C6-NBD-glucosyl-ceramide. An analysis of the fluorescence pattern after 1 h at 20 degrees C by means of a confocal scanning laser fluorescence microscope revealed that the fluorescent marker most likely concentrated in the Golgi complex itself. Little fluorescence was observed at the plasma membrane. Raising the temperature to 37 degrees C for 1 h resulted in intense plasma membrane staining and a loss of fluorescence from the Golgi complex. Addition of BSA to the apical medium cleared the fluorescence from the apical but not from the basolateral plasma membrane domain. The basolateral fluorescence could be depleted only by adding BSA to the basal side of a monolayer of MDCK cells grown on polycarbonate filters. We conclude that the fluorescent sphingomyelin and glucosylceramide were delivered from the Golgi complex to the plasma membrane where they accumulated in the external leaflet of the membrane bilayer. The results also demonstrated that the fatty acyl labeled lipids were unable to pass the tight junctions in either direction. Quantitation of the amount of NBD-lipids delivered to the apical and the basolateral plasma membranes during incubation for 1 h at 37 degrees C showed that the C6-NBD-glucosylceramide was two- to fourfold enriched on the apical as compared to the basolateral side, while C6-NBD-sphingomyelin was about equally distributed. Since the surface area of the apical plasma membrane is much smaller than that of the basolateral membrane, both lipids achieved a higher concentration on the apical surface. Altogether, our results suggest that the NBD-lipids are sorted in MDCK cells in a way similar to their natural counterparts.

The Membranes of Cells

Abstract: The lipids of cell membranes membrane models and model membranes lipid properties in membranes cholesterol and cell membranes membrane proteins lipid-protein interactions and the roles of lipids in biological membranes transport membrane fusion membrane receptors the metabolism of membrane lipids membrane biogenesis.

Quantitative contributions of cholesterol and the individual classes of phospholipids and their degree of fatty acyl (un)saturation to membrane fluidity measured by fluorescence polarization.

Abstract: Steady-state fluorescence polarization (P) measurements, using the probe 1,6-diphenyl-1,3,5-hexatriene, in a large variety of well-defined liposomes at 25 degrees C allowed a quantitative description of the contributions of cholesterol, sphingomyelin, and (un)saturation of fatty acyl groups in the various phospholipids to the structural order (or the mutual affinity) of membrane lipids The P values for liposomes prepared from lipid extracts of natural (purified) membranes of various origins could be more or less predicted (calculated) from the relative contributions of the individual lipid components In all cases, the polarization varied with the cholesterol/phospholipid molar ratio (C/PL) according to the equation P = Pplat -(Pplat -Pzero) exp(-alpha C/PL), in which Pzero refers to the polarization without cholesterol and Pplat is a maximal plateau value, reached at a high C/PL (greater than 1) The "cholesterol-ordering coefficient" alpha of the phospholipids was found to increase with the fraction of sphingomyelin or dipalmitoylphosphatidylcholine molecules, indicating that the susceptibility of phospholipids to be ordered by cholesterol is increased by these compounds Pzero increases curvilinearly with the fraction of either of these molecules Pplat increases linearly with the fraction of saturated acyl chains for most phospholipids Highly unsaturated fatty acyl chains (eg, 20:4 and 22:6) strongly depress Pplat but not Pzero The results suggest that such phospholipids are unlikely to associate with cholesterol and may thus create extremely fluid membrane domains The disproportionation of cholesterol in the cell can be understood by the differing composition of the phospholipids in plasma membranes and endomembranes and their ordering susceptibility (affinity) toward cholesterol

Effects of hemoglobin and cell membrane lipids on pulmonary surfactant activity

Abstract: These experiments characterize the effects of hemoglobin and erythrocyte membrane lipids on the dynamic surface activity and adsorption facility of whole lung surfactant (LS) and a calf lung surfac...

How membrane chain melting properties are regulated by the polar surface of the lipid bilayer.

Abstract: The principle of regulation of various membrane properties by the hydrocarbon membrane interior is now well understood. The mechanism by which the interfacial membrane region including aqueous solution affects the state of the lipid bilayer matrix, however, is as yet unclear, despite its great biological and physiological significance. Data and analysis presented in this paper show that apart from the lipid chain type, length, and degree of unsaturation the main factors determining the characteristics of lipid membranes are surface polarity and interfacial hydration. These incorporate the effects of head group dipole and multipole moments as well as the head group ability for hydrogen bonding and can account for most of the changes in the physicochemical membrane state caused by the lipid head group structure, bulk pH value, salt content, solute adsorption, etc. The effects of membrane potential are much less, only 10-30% of the former. Variations in hydration thus not only govern the short- and medium-range intermolecular and intermembrane interactions but also provide a fast and energetically inexpensive regulatory mechanism for lipid membranes to adapt their characteristics, at least locally or transiently, to new requirements.

Biosynthesis, membrane association, and release of N-CAM-120, a phosphatidylinositol-linked form of the neural cell adhesion molecule.

Abstract: The neural cell adhesion molecule (N-CAM) of rodents comprises three distinct proteins of Mr 180,000, 140,000, and 120,000 (designated N-CAM-180, -140, and -120). They are expressed in different proportions by different tissues and cell types. but the individual contribution of each form to cell adhesion is presently unknown. Previous studies have shown that the two N-CAM species of higher relative molecular mass span the membrane whereas N-CAM-120 lacks a transmembrane domain and can be released from the cell surface by phosphatidylinositol-specific phospholipase C. In this report, we provided evidence that N-CAM-120 contained covalently bound phosphatidylinositol and studied N-CAM-120 from its biosynthesis to its membrane insertion and finally to its release from the cell surface. Evidence was presented showing that the lipid tail of N-CAM-120 contained ethanolamine as is the case for other lipid-linked molecules. The phospholipid anchor was attached to the protein during the first minutes after completion of the polypeptide chain. This process took place in the endoplasmic reticulum as judged from endoglycosidase H digestion experiments. Immediately after a 2-min pulse with [35S]methionine, we detected also a short-lived precursor that had not yet acquired the lipid tail. Pulse-chase studies established that N-CAM-120 was transported to the cell surface from which it was slowly released into the extracellular milieu. The molecules recovered in the incubation medium appeared to have lost all of their bound fatty acid but only around half of the ethanolamine. Upon fractionation of brain tissue, approximately 75% of N-CAM-120 was recovered with a membrane fraction and approximately 25% in a membrane-free supernatant. A small proportion (approximately 6%) was found to be resistant to extraction by non-ionic detergent. A major posttranslational modification of N-CAM is polysialylation. Our results showed that also N-CAM-120 was polysialylated in the young postnatal brain and released in this form from cultured cerebellar cells. The presence of N-CAM in a form that can be released from the cell surface and accumulates in the extracellular fluid suggests a novel mechanism by which N-CAM-mediated adhesion may be modulated.

Al3+ and Ca2+ Alteration of Membrane Permeability of Quercus rubra Root Cortex Cells

Abstract: This study was undertaken to quantify the effect of aluminum and calcium on membrane permeability. The influence of Ca 2+ (0.2-3.7 millimolar) and Al 3+ (0-3.7 millimolar) on the permeability of root cortical cells of Quercus rubra was measured using three nonelectrolytes (urea, methyl urea, and ethyl urea) as permeators of progressively increasing lipid solubility. Water permeability was also measured. Al 3+ (a) increased membrane permeability to the nonelectrolytes, (b) decreased the membrane9s partiality for lipid permeators, and (c) decreased membrane permeability to water. Ca 2+ had effects on permeability that were opposite to those of Al 3+ . When Al 3+ and Ca 2+ were tested in combination, these opposite effects counteracted each other. The results suggest that Al 3+ altered the architecture of membrane lipids.

Lipid fluidity and membrane protein dynamics

Abstract: Membrane fluidity plays an important role in cellular functions. Membrane proteins are mobile in the lipid fluid environment; lateral diffusion of membrane proteins is slower than expected by theory, due to both the effect of protein crowding in the membrane and to constraints from the aqueous matrix. A major aspect of diffusion is in macromolecular associations: reduction of dimensionality for membrane diffusion facilitates collisional encounters, as those concerned with receptor-mediated signal transduction and with electron transfer chains. In mitochondrial electron transfer, diffusional control is prevented by the excess of collisional encounters between fast-diffusing ubiquinone and the respiratory complexes. Another aspect of dynamics of membrane proteins is their conformational flexibility. Lipids may induce the optimal conformation for catalytic activity. Breaks in Arrhenius plots of membrane-bound enzymes may be related to lipid fluidity: the break could occur when a limiting viscosity is reached for catalytic activity. Viscosity can affect protein conformational changes by inhibiting thermal fluctuations to the inner core of the protein molecule.

Stabilization of acetylcholine receptor secondary structure by cholesterol and negatively charged phospholipids in membranes

Abstract: Fourier-transform infrared (FTIR) spectroscopy was used to study the secondary structure of purified Torpedo californica nicotinic acetylcholine receptor (AChR) in reconstituted membranes. Functional studies have previously demonstrated that the ion channel activity requires the presence of both sterol and negatively charged phospholipids in membranes. The present studies are designed to test the hypothesis that the alpha-helical structure of AChR may be stabilized by specific lipid molecules (sterol and/or negatively charged phospholipids) and that these alpha-helices may be responsible for the formation of a potential ion channel. FTIR data show statistically significant (p less than 0.005) spectral changes due to cholesterol and negatively charged phospholipids, respectively. On the basis of standard curves describing the relationship between the spectral properties and the secondary structural contents of water-soluble proteins, the observed spectral change at 931 cm-1 can be interpreted as an apparent change in the alpha-helix content from about 17% in the absence of sterols to about 20% in the presence of sterols, suggesting that protein-sterol interactions increase the helical structure of the AChR molecule. Similarly, the spectral change at 988 cm-1 can be interpreted as an apparent increase of beta-sheet content in the AChR molecule from about 20% to about 24% due to the presence of negatively charged phospholipids. Functional AChR in membranes thus appears to be correlated with higher alpha-helical and beta-sheet contents. It is concluded that one role of specific interactions between membrane protein and lipid molecules may be to maintain specific secondary structures necessary to support the ion channel function of AChR.

High lateral mobility of endogenous and transfected alkaline phosphatase: a phosphatidylinositol-anchored membrane protein.

Abstract: The lateral mobility of alkaline phosphatase (AP) in the plasma membrane of osteoblastic and nonosteoblastic cells was estimated by fluorescence redistribution after photobleaching in embryonic and in tumor cells, in cells that express AP naturally, and in cells transfected with an expression vector containing AP cDNA. The diffusion coefficient (D) and the mobile fraction, estimated from the percent recovery (%R), were found to be cell-type dependent ranging from (0.58 +/- 0.16) X 10(-9) cm2s-1 and 73.3 +/- 10.5 in rat osteosarcoma cells ROS 17/2.8 to (1.77 +/- 0.51) X 10(-9) cm2s-1 and 82.8 +/- 2.5 in rat osteosarcoma cells UMR106. Similar values of D greater than or equal to 10(-9) cm2s-1 with approximately 80% recovery were also found in fetal rat calvaria cells, transfected skin fibroblasts, and transfected AP-negative osteosarcoma cells ROS 25/1. These values of D are many times greater than "typical" values for membrane proteins, coming close to those of membrane lipid in fetal rat calvaria and ROS 17/2.8 cells (D = [4(-5)] X 10(-9) cm2s-1 with 75-80% recovery), estimated with the hexadecanoyl aminofluorescein probe. In all cell types, phosphatidylinositol (PI)-specific phospholipase C released 60-90% of native and transfection-expressed AP, demonstrating that, as in other tissue types, AP in these cells is anchored in the membrane via a linkage to PI. These results indicate that the transfected cells used in this study possess the machinery for AP insertion into the membrane and its binding to PI. The fast AP mobility appears to be an intrinsic property of the way the protein is anchored in the membrane, a conclusion with general implications for the understanding of the slow diffusion of other membrane proteins.

Effect of growth temperature on the lipids, outer membrane proteins, and lipopolysaccharides of Pseudomonas aeruginosa PAO.

Abstract: Growth of Pseudomonas aeruginosa PAO1 at 15 to 45 degrees C in tryptic soy broth resulted in changes in the lipids, lipopolysaccharides (LPSs), and outer membrane proteins of the cells. Cells grown at 15 degrees C contained, relative to those cultivated at 45 degrees C, increased levels of the phospholipid fatty acids hexadecenoate and octadecenoate and reduced levels of the corresponding saturated fatty acids. Furthermore, the lipid A fatty acids also showed thermoadaptation with decreases in dodecanoic and hexadecanoic acids and increases in the level of 3-hydroxydecanoate and 2-hydroxdodecanoate as the growth temperature decreased. In addition, LPS extracted from cells cultivated at the lower temperatures contained a higher content of long-chain S-form molecules than that isolated from cells grown at higher temperatures. On the other hand, the percentage of LPS cores substituted with side-chain material decreased from 37.6 mol% at 45 degrees C to 19.3 mol% at 15 degrees C. The outer membrane protein profiles indicated that at low growth temperatures there was an increase in a polypeptide with an apparent molecular weight of 43,000 and decreases in the content of 21,000 (protein H1)- and 27,500-molecular-weight proteins.

Effect of lipid surface charges on the purple-to-blue transition of bacteriorhodopsin.

Abstract: Purple membrane (lambda max = 568 nm) can be converted to blue membrane (lambda max = 605 nm) by either acid titration or deionization. Partially delipidated purple membrane, containing only 25% of the initial lipid phosphorus, could be converted to a blue form by acid titration but not by deionization. This reversible transition of delipidated membrane did not require the presence of other cations, and the pK of the color change that in native membrane under similar conditions is between 3.0 and 4.0 was shifted to 1.4. We conclude that the purple-to-blue transition is controlled by proton concentration only and that, in native membranes, the cations act only by raising the low surface pH generated by the acidic groups of the lipids. The observation that extraction of lipids from deionized native membrane converts its color from blue to purple further confirms this conclusion. The two states of the membrane probably reflect two preferred conformations of bacteriorhodopsin, which are controlled by protonation changes at the surface of the membrane and differ slightly in the spatial distribution of charges around the chromophore.

Reconstitution of a phospholipid flippase from rat liver microsomes

Abstract: The endoplasmic reticulum is the principal site of synthesis and initial incorporation of membrane lipids in eukaryotic cells; the enzymes of glycerolipid biosynthesis are exclusively located on its cytoplasmic surface. To maintain a phospholipid bilayer in this organelle, newly synthesized phospholipids must be translocated to the lumenal surface. Consistent with this are measurements indicating that movement of phospholipids across microsomal membranes is rapid, with a half-time less than 5 min (refs 3 and 4). Rapid movement of phospholipids has also been detected across the plasma membrane of Bacillus megaterium, another site of de novo lipid biosynthesis. The rapid transmembrane movement of phosphatidylcholine has not been detected, however, in vesicles prepared from microsomal lipids. These latter data suggest involvement in the endoplasmic reticulum of a phospholipid-translocating protein, as was first proposed by Bretscher who called it 'flippase'. Here we report reconstitution of a phospholipid flippase from rat liver microsomes into lipid vesicles.

Release of outer membrane fragments by exponentially growing Brucella melitensis cells

Abstract: Rough and smooth strains of Brucella melitensis released a membranous material that was devoid of detectable NADH oxidase and succinic dehydrogenase activity (cytoplasmic membrane markers) but that contained lipopolysaccharide, proteins, and phospholipids. This material was composed of two fractions that had similar chemical compositions but that were of different sizes which were separated by differential ultracentrifugation. Electron microscopy showed that both fractions are made of unit membrane structures. The membrane fragments were released during the exponential phase of growth, and no leakage of malic dehydrogenase activity (cytosol marker) was detected. Thus, the fragments were unlikely a result of cell lysis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis showed that, although group 2 Brucella outer membrane proteins and lipoprotein were not detected, the proteins in the membranous material were outer membrane proteins. Gas-liquid chromatography analysis showed a similar fatty acid profile for the cell envelope and the outer membrane fragments of the smooth strain B. melitensis 16M. In contrast, the outer membrane fragments from the rough 115 strain were enriched in palmitic and stearic acids. With respect to the unfractionated cell envelope, outer membrane fragments were enriched in phosphatidylcholine, a phospholipid that is unusual in bacterial membranes.

Activation of mouse peritoneal macrophages by lysophospholipids and ether derivatives of neutral lipids and phospholipids.

Abstract: Cellular damage and inflammatory processes cause activation of phospholipase A in plasma membranes resulting in the production of various lysophospholipids Treatment of mice with L-alpha-lysophosphatidylcholine, a decomposition product of phosphatidylcholine, greatly stimulates mouse peritoneal macrophages to ingest target cells via the Fc receptors Similarly, treatment of mice with L-alpha-lysophosphatidylethanolamine and L-alpha-lysophosphatidyl-L-serine resulted in an enhanced ingestion activity of macrophages Cancer cell membranes contain alkyl ether derivatives of phospholipids and neutral lipids Inflamed cancer cells release decomposition products of alkyl ether phospholipids and neutral lipids, alkyl-lysophospholipids and alkylglycerols, respectively Administration of alkyl ether analogues of lysophospholipids into mice were able to induce stimulation of macrophages for ingestion with Fc receptor preference Two synthetic alkylglycerols, dodecylglycerol and tridecylglycerol, were tested Dodecylglycerol induced an efficient stimulation of macrophages for Fc-mediated ingestion whereas tridecylglycerol induced a minimal level of activation Therefore, in vivo effect of dodecylglycerol on macrophage stimulation is similar to that of lysophospholipids and their alkyl analogues These in vivo stimulations of macrophages for Fc receptor-mediated ingestion activity were reproduced in in vitro activation of macrophages by treatment of peritoneal cells with the alkyl lipid derivatives Among these compounds, dodecylglycerol was found to be the most potent agent for macrophage stimulation Since macrophages are antigen-presenting cells, the degradation products of cancer cell membrane lipids may have immune potentiating capacity

The effects of reduced amounts of lipid unsaturation on chloroplast ultrastructure and photosynthesis in a mutant of Arabidopsis.

Abstract: A mutant of Arabidopsis thaliana with reduced content of C(18:3) and C(16:3) fatty acids in membrane lipids exhibited a 45% reduction in the cross-sectional area of chloroplasts and had a decrease of similar magnitude in the amount of chloroplast lamellar membranes. The reduction in chloroplast size was partially compensated by a 45% increase in the number of chloroplasts per cell in the mutant. When expressed on a chlorophyll basis the rates of CO(2)-fixation and photosynthetic electron transport were not affected by these changes. Fluorescence polarization measurements indicated that the fluidity of the thylakoid membranes was not significantly altered by the mutation. Similarly, on the basis of temperature-induced fluorescence yield enhancement measurements, there was no significant effect on the thermal stability of chlorophyll-protein complexes in the mutant. These observations suggest that the high content of trienoic fatty acids in chloroplast lipids may be an important factor regulating organelle biogenesis but is not required to support normal levels of the photosynthetic activities associated with the thylakoid membranes.

Membrane fatty acid modification in tumor cells: a potential therapeutic adjunct.

Abstract: The fatty acid compositions of several tumors have been modified sufficiently to alter some of their properties and functions. These modifications were produced in culture by adding specific fatty acids to the growth medium or by feeding fat-supplemented diets to tumor-bearing mice. The phospholipid fatty acid composition of the plasma membrane was modified, but there were no changes in membrane phospholipid or cholesterol content or in phospholipid head group composition. Each of the most abundant membrane phosphoglyceride fractions exhibited some degree of fatty acid modification. Electron spin resonance measurements with nitroxystearate spin probes indicated that the fatty acid modifications were sufficient to alter the physical properties of the plasma membrane. The K'm for methotrexate uptake was reduced when the L1210 leukemia cells were enriched in linoleic acid. Even when the kinetics of uptake at 37 C were not altered, such as for melphalan and phenylalanine uptake, the temperature transition of transport was modified, indicating that these transport systems also are responsive to the membrane fatty acid modifications. Enrichment with highly polyunsaturated fatty acid did not affect either the growth rate or radiosensitivity of the L1210 leukemia. However, the sensitivity of the L1210 cells to the cytotoxic effects of Adriamycin and hyperthermia was increased. These findings suggest the possibility that fatty acid modification of tumors may be a useful adjunct to certain currently available therapeutic modalities.

Intracellular lipid transport in eukaryotes.

Abstract: The metabolic regulation and biological significance of the large number of lipid species found in all biological membranes are not well understood. It has been estimated that there are greater than 1000 chemically distinct phospho­ lipid species in eukaryotic cells (98), all of which must bestow significant evolutionary advantages to the cells. The majority of lipids are synthesized at the endoplasmic reticulum (ER) , and yet most lipid species are found through­ out the cell, with organelles having differing lipid compositions and display­ ing an asymmetric distribution of lipid species across their bilayers. An increased interest in the cell biology of lipids has arisen from the realization that lipid molecules act as modulators of a large number of biological pro­ cesses (93). The maintenance of the complex intracellular distribution of lipids is most likely regulated by several processes, including specific lipid transport mechanisms. The identification of these transport mechanisms in living cells has proven to be a difficult problem and is the subject of this brief review. The three general mechanisms believed to be responsible for intracellular lipid transport between membranes are: (a) vesicular transport, the transport of molecules from one organelle to another by vesicles budding and fusing; (b) monomer transport, the transport of single lipid molecules between membranes through the cytoplasm (this transport may be either spontaneous or protein assisted); (c) lateral diffusion, the transport of molecules within the plane of the membrane bilayer between two organelles connected by bridges. Lipid molecules may also undergo transmembrane movement, transferring between leaflets of a membrane'S lipid bilayer.

Rotational and Lateral Diffusion of Membrane Proteins and Lipids: Phenomena and Function

Abstract: Publisher Summary Motion of cell membrane components occurs over a wide range of time and distance scales. This chapter discusses the rotational and translational diffusion of membrane lipids and proteins and motions over a part of the time and distance scales. The short-range and rapid motions, especially of membrane lipids are summed up in terms of viscosity or fluidity. The chapter describes rotational motions in the range of 106 to 103 sec-1 and with lateral movements in the range of 10-12 to 10-7 cm2 sec-1. Methods for measuring diffusion and some of the results obtained with these methods are described. It discusses the biological functions of diffusion in membranes. All the techniques for measuring diffusion depend upon some aspects of the spectra of selected probes. These probes may be roughly divided into optical probes and magnetic resonance probes. The methods used for measuring rotational diffusion are optical method and saturation-transfer electron-spin resonance (ESR) (S-T ESR). Rotation of erythrocyte band 3, bacterio- and vertebrate rhodopsin, calcium ATPase of sarcoplasmic reticulum, cytochromes and cytochrome oxidases, and acetylcholine receptor have been measured in native and synthetic membranes. These measurements yield information on protein–protein association as a function of membrane protein concentration, on coupling of integral membrane proteins with the cell cytoskeleton, and on coupling of enzymatically interacting components. All methods for lateral diffusion take one of the two approaches: measurement of the frequencies of molecular encounter or measurement of the time required for marked molecules to fill a defined area of membrane.

Patterns of lipid changes in membranes of the aged brain.

Abstract: The lipid composition of cell plasma membranes reflects a steady-state between accumulation of serum lipids, predominantly cholesterol, and intracellular lipid synthesis and degradation. In the aging tissue this subtle balance is impaired with a net accumulation of cholesterol and other rigidifying lipids such as sphingomyelin in the membrane. As a consequence, most membrane processes, including ion transports in neuronal tissues, are slowed down. In principle, it is possible to rectify such adversative processes in vivo by increasing the level of specific phospholipids and glycerides in the serum.

Peptides in membranes: lipid-induced secondary structure of substance P.

Abstract: Substance P (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2), a neuromodulator involved in the transmission of pain information, exerts its biological effects by binding to membrane-embedded protein receptors. The influence of membrane lipids on neuropeptide conformation may be critical to these processes. We have characterized in detail the complexes formed between substance P and sodium dodecylsulfate (SDS), lysophosphatidylglycerol, and lysophosphatidylcholine micelles. CD spectra of substance P displayed significant induced secondary structure upon addition of these lipids. Potentiometric titration data demonstrated that the pKa of the peptide N-terminal amino group increased from ca. 7.0 to 9.0 in SDS-bound substance P, suggesting direct interaction of the substance P N-terminus with the lipid head-group region. Red shifts in uv spectra of the Phe rings in membrane-bound peptide suggested an increased hydrophobic environment for these substituents. High-resolution one- and two-dimensional correlated spectroscopy nmr spectra displayed differential chemical-shift movements of substance P Gln, Leu, and Met NH protons with added lipid, suggesting involvement of the C-terminal portion of the peptide in the induced secondary structure. The clear influence of the lipid environment on the substance P conformational ensemble suggests a role for the membrane in the events leading to receptor binding.