Increasing Acyl Chain Length Research Articles

Combining site specificities of rabbit antibodies to platelet-activating factor (PAF)

Anti-PAF sera from six different rabbits, immunized with C 12- or C 6-PAF as immunogen, were examined in hapten inhibition experiments in an attempt to define the fine structural recognition specificities of the antibody combining sites. Using a selection of naturally occurring lipids and PAF analogues, no significant cross-reactivity was observed with the lipids or with the inactive metabolite, lyso-PAF. Comparison of the structural specificity requirements of the antibodies from each rabbit showed some heterogeneity, with one antiserum demonstrating a different recognition specificity at position 1 on the glycerol backbone of the PAF molecule. A second rabbit antiserum showed a large degree of tolerance for analogues with increasing acyl chain length at position 2. In general, an ether group at position 1 and an acetyl at position 2 were required for inhibitory activity and a degree of tolerance was demonstrated at position 3, where the main structural requirement was for one or more methyl groups on the nitrogen atom of the phosphocholine moiety.

Kinetics and mechanism of transfer of synthetic model apolipoproteins.

The effect of hydrophobicity on the rate and mechanism of transfer of a synthetic amphiphilic peptide between phosphatidylcholine single bilayer vesicles has been evaluated. These peptides, which had the sequence Cn-SSLKEYWSSLKESFS (where Cn represents a saturated acyl chain of n carbons that is attached to the amino terminus of the peptide and n = 8, 12, or 16), were distinguished by the length of the saturated acyl chain of n carbons that was covalently bonded to the amino terminus. The transfer of the peptides was monitored by following the rate of change of the intrinsic tryptophan fluorescence that followed mixing of donor vesicles, which contained peptide, phosphatidylcholine, and a fluorescence quencher, with acceptors composed only of phosphatidylcholine. The transfer rates were independent of the structure and concentration of the acceptor. The kinetics were biexponential with the contribution of the fast and slow components being nearly equal. The rates of both components decreased with increasing acyl chain length; the respective free energies of activation were linear with respect to the acyl chain length. These results showed that, unlike lipid transfer, peptide transfer is not always a simple unimolecular process. However, like lipid transfer, the transfer rates are a predictable function of hydrophobicity. It is proposed that the peptides exist as dimers on the phospholipid surface and that the two components of transfer are due to sequential transfer of each molecule in a dimer.

The physical properties of glycosyldiacylglycerols. Calorimetric studies of a homologous series of 1,2-di-O-acyl-3-O-(beta-D-glucopyranosyl)-sn-glycerols.

The polymorphic phase behavior of aqueous dispersions of a homologous series of 1,2-di-O-acyl-3-O-(beta-D-glucopyranosyl)-sn-glycerols was studied by differential scanning calorimetry. At fast heating rates, unannealed samples of these lipids exhibit a strongly energetic, lower temperature transition, which is followed by a weakly energetic, higher temperature transition. X-ray diffraction studies have enabled the assignments of these events to a lamellar gel/liquid crystalline (chain-melting) phase transition and a bilayer/nonbilayer phase transition, respectively. Whereas the values for both the temperature and enthalpy of the chain-melting phase transition increase with increasing acyl chain length, those of the bilayer/nonbilayer phase transition show almost no chain-length dependence. However, the nature of the bilayer/nonbilayer transition is affected by the length of the acyl chain. The shorter chain compounds form a nonbilayer 2-D monoclinic phase at high temperature whereas the longer chain compounds from a true inverted hexagonal (HII) phase. Our studies also show that the gel phase that is initially formed on cooling of these lipids is metastable with respect to a more stable gel phase and that prolonged annealing results in a slow conversion to the more stable phase after initial nucleation by incubation at appropriate low temperatures. The formation of these stable gel phases is shown to be markedly dependent upon the length of the acyl chains and whether they contain an odd or an even number of carbon atoms. There is also evidence to suggest that, in the case of the shorter chain compounds at least, the process may proceed via another gel-phase intermediate. In annealed samples of the shorter chain compounds, the stable gel phase converts directly to the L alpha phase upon heating, whereas annealed samples of the longer chain glycolipids convert to a metastable gel phase prior the chain melging.(ABSTRACT TRUNCATED AT 250 WORDS)

Transbilayer diffusion of phospholipids: dependence on headgroup structure and acyl chain length

The kinetics and thermodynamics of the transmembrane movement (flip-flop) of fluorescent analogs of phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylcholine(PC), and phosphatidylethanolamine (PE) were investigated to determine the contributions of headgroup composition and acyl chain length to phospholipid flip-flop. The phospholipid derivatives containing n- octanoic , n- decanoic or n- dodecanoic acid in the sn- 1 position and 9-(1-pyrenyl)nonanoic acid in the sn- 2 position were incorporated at 3 mol% inot sonicated single-bilayer vesicles of 1-palmitoyl-2-oleoyl-sn- glycerol-3-phosphocholine (POPC). The kinetics of diffusion of the pyrene-labeled phospholipids from the outer and inner monolayers of the host vesicles to a large pool of POPC acceptor vesicles were monitored by the time-dependent decrease of pyrene excimer fluorescence. The observed kinetics of transfer were biexponential, with a fast component due to the spontaneous transfer of pyrenyl phospholipids in the outer monolayer of labeled vesicles and a slower component due to diffusion of pyrenyl phospholipid from the inner monolayer of the same vesicles. Intervesicular transfer rates decreased approx. 8-fold for every two carbons added to the firs acyl chain. Corrrespondingly, the free energy of activation for transfer increased approx. 1.3 kcal/mol. With the exception of PE, the intervesicular transfer rates for the different headgroups within a homologous series were nearly the same, with the PC derivative being the fastest. Transfer rates for the PE derivatives were 5- to 7-fold slower than the rates observed for PC. Phospholipid flip-flop, in contrast, was strongly dependent on headgroup composition with a smaller dependence on acyl chain length. At pH 7.4, flip-flop rates increased in the order PC < PG < PA < PE, where the rates for PE were at least 10-times greater than those of the homologous PC derivative. Activation energies for flip-flop were large, and ranged from 38 kcal/mol for the longest acyl chain derivative of PC to 25 kcal/mol for the PE derivatives. Titration of the PA headgroup at pH 4.0 produced an approx. 500-fold increase in the flip-flop rate of PA, while the activatiion energy decreased 10 kcal/mol. Increasing acyl chain length reduced phospholipid flip-flop rates, with the greatest change observed for the PC analogs, which exhibited an approx. 2-fold decrease in flip-flop rate for every two methylene carbons added to the acyl chain at the sn- 1 position. Our results suggest that the insolubility of the polar headgroup in the membrane interior is the major barrier to flip-flop. The contribution of the apolar portion of the phospholipid to flip-flop is less significant.

Specific free fatty acids induce larval settlement and metamorphosis of the reef-building tube worm Phragmatopoma califomica (Fewkes)

Planktonic larvae of the Californian reef-building sabellariid polychaete worm, Phragmatopoma califomica, settle and metamorphose in the presence of specific free fatty acids (FFAs) isolated from the sand matrix of adult tubes. Thirty-seven commercially-available FFAs of increasing acyl chain length and of variable unsaturation were assayed for their capacity to induce larval metamorphosis. At 100 μg FFA/g sand, settlement and metamorphosis peaked in response to palmitoleic acid (16:1; 24.5 % metamorphosis versus 0.8% metamorphosis in control assays), linolenic acid (18:3, 24.9% metamorphosis), eicosapentaenoic acid (20:5; 16.9% metamorphosis) and docosahexaenoic acid (22:6; 8.7% metamorphosis), and decreased as the acyl chain length or the number of double bonds was changed. Palmitelaidic acid, the trans isomer of palmitoleic acid, was ineffective at inducing a larval response. Assays of the monoglycerides and methyl esters of palmitoleic and linoleic acids, cis-9-hexadecen-1-ol, cis-9,12-octadecadien-1-ol, the corresponding acetates and cis-9,12-octadecadiene resulted in little or no larval metamorphosis. Larval response is dependent on (1)the presence of at least one cis double bond in the molecule, (2) conservation of molecular shape with increasing acyl chain length by addition of cis double bonds, and (3) the presence of a free carboxyl group. This specificity resembles that found in studies of insect chemoreception and suggests that receptors may similarly mediate larval response in this marine invertebrate.

Thermodynamics and kinetics of phospholipid monomer-vesicle interaction.

Resonance energy transfer between acyl chain labeled (7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylcholine (NBD-PC) and head group labeled (lissamine rhodamine B sulfonyl)phosphatidylethanolamine (N-Rh-PE) was used to monitor the rate of NBD-PC transfer between two populations of dioleoylphosphatidylcholine (DOPC) vesicles. Equilibration of NBD-PC between DOPC vesicles occurs by the diffusion of soluble monomers through the water phase, which is a first-order process. Conditions were used such that the apparent transfer rate constant is equal to the rate constant for monomer-vesicle dissociation into solution. The partition distribution of NBD-PC between DOPC vesicles and water was determined by measuring the loss of NBD-PC from vesicles into solution following the dilution of small amounts of vesicles in buffer. The acyl chain length and temperature dependence of both the rate and partition measurements were determined, and a free energy diagram for NBD-PC-soluble monomer-vesicle interactions was constructed. The conclusions of this analysis are the following: NBD-PC dissociation from and association with the bilayer require passage through a high-energy transition state resulting predominantly from enthalpic energy. The activation energy for NBD-PC-vesicle dissociation becomes more positive and the standard free energy of NBD-PC transfer from water to vesicles becomes more negative with increasing acyl chain length. The standard free energy of transfer for NBD-PC from water to vesicles results predominantly from differences in enthalpy between the membrane and water phases. The enthalpy of activation for association increases with acyl chain length and is larger than expected for an aqueous diffusion-limited process in bulk water.

Influence of Physicochemical Interactions on the Properties of Suppositories, II, Interactions Between the Constituents of Fatty Suppository Bases and Ketoprofen or Metronidazole

AbstractThe rate at which drugs are released from suppositories and absorbed by the rectal mucosa tends to decrease with increasing solubility of drug in the base or increasing strength of interaction between them. The solubility of ketoprofen or metronidazole in various molten mono-acid triglyceride constituents of fatty suppositories was determined at various temperatures and extrapolated to 37°C and to 100°C. With increasing acyl chain length of the triglyceride solvent the solubility of both drugs tended to decrease and the enthalpy and entropy of solution, determined by van't Hoff or Hildebrand plots, tended to become increasingly positive. The solubility data did not accord with regular solution theory, indicating that specific solute-solvent interactions are important in the solutions. The Rf values of the drugs were determined on triglyceride-impregnated layers of silica gel using water: methanol: glacial acetic acid (10:10: 1 v/v) as the moving phase. For ketoprofen the rank order of the Rf value...

Kinetic and thermodynamic studies of the fusion of small unilamellar phospholipid vesicles

Small phospholipid vesicles, prepared so as to minimize impurities, fuse relatively slowly resulting in the time-dependent development of a characteristic endotherm in differential scanning calorimetry and corresponding changes in the Raman spectrum. The stability of small vesicles towards fusion increases with increasing acyl chain length for the series C-14 through 18. Within the protocols of these experiments, the fusion rate remains unchanged whether the vesicles are held at 10°C below T m or at T m itself. We have determined enthalpies of transition for small vesicles and fusion product for C-14 through C-18. In each case ΔH for small vesicles is lower than that of the corresponding multilamellar vesicles, while the fusion product ΔH is intermediate between small and multilamellar vesicles. The apparent lack of concensus in the literature as to the nature of the fusion process is ascribed to the variety of protocols used as well as the presence or absence of fusion-inducing impurities.

Micelle formation in aqueous n-alkanoate solutions: A fourier transform infrared study

The concentration dependencies of the infrared spectra of deuterium oxide solutions of sodium propionate, n-butyrate, n-pentanoate, n-hexanoate, n-heptanoate, n-octanoate, nnonanoate, and n-decanoate have been determined in concentration ranges encompassing the critical micelle concentrations. Progressively decreasing premicellar aggregation with increasing acyl chain length is demonstrated, with there being no evidence for premicellar aggregation in the sodium octanoate, nonanoate, and decanoate solutions. The frequencies and widths of the C-H stretching bands indicate that the acyl chains are conformationally disordered in the micellar phase, to a degree similar to that in liquid alkanes. They also indicate that, in the micellar phase, there is little or no hydrocarbon chain-water contact.

Thermodynamics of partitioning and efflux of phenothiazines from liposomes.

The partitioning of nine phenothiazines between dimyristoylphosphatidylcholine (DMPC) liposomes and 0.9% wt/vol saline at pH 6 has been studied both below and above the phase transition temperature (Tc) of the phospholipid. Higher partitioning was observed above Tc. Both the entropy and enthalpy of partitioning were positive below and above Tc, and a linear relationship between the entropy and enthalpy has been derived. In general, the partitioning and transport of alkylaminophenothiazines in DMPC liposomes over the temperature range of 5 to 40 degrees C is entropically controlled. The entropies and enthalpies of partitioning of various groups in the phenothiazine structure have been calculated. No relationship was found between particle size of the DMPC liposomes and the equilibrium partition coefficient at 25 degrees C. However, the particle size of liposomes did increase with increasing acyl chain length of the phospholipid. Using differential scanning calorimetry, the enthalpy and entropy of transition of the DMPC liposomes in the absence and presence of phenothiazines has been calculated. The temperature dependence of the first-order rate constant of trimeprazine tartrate transport in DMPC liposomes was investigated and was found to be maximum at the Tc of the phospholipid.

YEAST ESTERASES AND AROMA ESTERS IN ALCOHOLIC BEVERAGES

It has been shown that the proportion of fatty acid ethyl esters retained by the yeast cell increases with increasing acyl chain length as the ester becomes more lipid soluble. The distribution of esters depends on the yeast strain and on the fermentation temperature; larger amounts of esters were found to transfer from the cells into the medium at higher temperature. It was shown that esterase activity is located both inside and outside the yeast cell plasma membrane. Intact yeast was capable of hydrolysing the ethyl esters of caproic, caprylic and capric acid. Acetate esters, were hydrolysed only very slowly or not at all. The hydrolytic activity of baker's yeast was studied with ethyl caprylate as substrate. The hydrolysis was very fast at the beginning. The equilibrium attained depended not only on the concentration of ester and alcohol but also on the pH, a higher amount of ester remaining in solutions of lower pH. It was also shown that the esterases possess appreciable ester synthesizing ability and an equilibrium was attained by incubating yeast with caprylic acid and ethanol. The experiments described show that the ester level in an alcoholic beverage, such as beer, is not dependent solely on the ester concentration formed during fermentation: in the presence of yeast the level can be shifted in either direction by changing temperature, pH or alcohol concentration — or the amount and type of yeast.

On the Mechanism of Membrane Damage by Complement: The Effect of Length and Unsaturation of the Acyl Chains in Liposomal Bilayers and the Effect of Cholesterol Concentration in Sheep Erythrocyte and Liposomal Membranes

Abstract As shown previously, the action of activated complement (C) on a lipid bilayer produces two distinct effects, namely, formation of transmembrane channels and transfer of phospholipid from the bilayer to the aqueous phase. In the present work, we show that both phenomena are affected by the structure of the membrane lipids. Increasing acyl chain length of lecithin liposomes containing cholesterol was found to decrease release of 86Rb+ by antibody (Ab) and C or by purified C5b,6 + C7 + C8 + C9. These changes in 86Rb+ release suggest that channel formation is affected by membrane thickness. Similarly, release of 14C-PC by Ab + C diminished with increasing acyl chain length. Release of 86Rb+ from egg lecithin liposomes by Ab + C was found to diminish with increasing cholesterol concentration. On the other hand, higher release of 14C-PC was observed with increasing cholesterol concentration. Cholesterol itself was not released by Ab + C. The effect of membrane cholesterol was also studied with sheep erythrocytes by incubation of the cells with a cholesterol-enriched medium. In accord with the results obtained with liposomes, the susceptibility of erythrocytes to hemolysis by C5b-9 was found to diminish with increasing cholesterol enrichment of the membrane, which indicates that cholesterol affects channel formation. The effect of unsaturation was tested by treatment of C18:0 or C18:1 lecithin liposomes containing 43% molar cholesterol with Ab + C. 86Rb+ release was decreased, whereas 14C-PC release was slightly increased when unsaturated chains were present. Membrane fluidity is not believed to be the sole controlling factor since the changes in this parameter by varying cholesterol or by unsaturation did not correlate with the effects on marker release.

Preparation and surface‐ active properties of polyoxyethylene‐glycol (600) monoesters of fatty acids

Abstract and SummaryPolyoxyethyleneglycol (PEG‐600) monoesters of undecylenic, lauric, myristic, palmitic, stearic, oleic, ricinoleic and 12‐hydroxystearic acids were prepared in 80‐85% yield by reacting PEG with boric acid, esterifying the resultant borate with fatty acid, and selectively hydrolyzing the borate ester; their surface active properties were evaluated. Increase in acyl chain length increased the surface tension. The presence of a double bond or hydroxyl group in C18 series improved the wetting and emulsifying proper‐ties. Unsaturation in the fatty acid chain reduced the foaming power.