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PubMed2002

Lipid A structures containing novel lipid moieties: synthesis and adjuvant properties.

Structurally well-defined immune stimulatory molecules are important components of new generation molecular vaccines. In this paper, the design and synthesis of two lipid A analogues containing an unnatural tri-lipid acyl group are described. In a totally synthetic liposomal vaccine system, these re-designed lipid A analogues demonstrate potent immune stimulatory properties including antigen specific T-cell activation.

Adjuvants, Immunologic↗

PubMed2001

1H NMR-visible mobile lipid domains correlate with cytoplasmic lipid bodies in apoptotic T-lymphoblastoid cells.

The presence of nuclear magnetic resonance (NMR)-visible mobile lipid (ML) domains in apoptotic lymphoblasts suggests alterations in neutral lipid metabolism and compartmentation during programmed cell death. The detection of similar ML signals in activated lymphocytes raises questions about common mechanisms of ML formation during apoptosis and upon lymphoblast stimulation. Structure and subcellular localization of ML domains were therefore investigated by NMR, fluorescence and electron microscopy in Jurkat T-lymphoblasts either induced to apoptosis (by anthracyclines or dexamethasone or by serum deprivation) or activated by phorbol myristate acetate (PMA) plus ionomycin. ML contents in drug-treated cells correlated linearly with apoptosis, irrespective of the specific inducer and cell cycle arrest phase (r = 0.993, P < 0.001). Similar ML levels were measured in drug-induced apoptotic cells (A approximately 30-40%) and in non-apoptotic PMA/ionomycin-treated lymphoblasts (72 h). Lower ML contents were instead formed in serum-deprived apoptotic cells, with respect to controls. Increases in ML signals were associated, in either apoptotic or activated cells, with the accumulation of cytoplasmic, osmophilic lipid bodies (diameter < or = 1.0 microm), surrounded by own membrane, possessing intramembrane particles. The results support the hypothesis that ML are formed in the cytoplasm of drug-induced apoptotic cells during an early, 'biochemically active' phase of programmed cell death.

Apoptosis↗

PubMedDate not supplied

Maleimide-functionalized lipids that anchor polypeptides to lipid bilayers and membranes.

Two maleimide-containing diacylglycerol derivatives were synthesized to permit the anchoring of short peptides and longer polypeptides to phospholipid bilayers and membranes. The maleimide was introduced at the site normally occupied by a phospholipid headgroup. The first lipid, the dipalmitoyl ester of 1-maleimido-2,3-propanediol, was developed as a membrane anchor for extracellular domains of transmembrane proteins. The second anchoring lipid, in which the 3-position contained a 6-aminohexanoate, was designed for convenient modification with amine-reactive reporter groups. Specifically, the NBD fluorophore, 7-nitrobenzo-2-oxa-1, 3-diazole-aminohexanoic-N-hydroxysuccinimide ester, was attached to give an fluorescent anchoring reagent. Next, these reagents were applied to the anchoring of a C-terminally cysteamine-modified 8 kDa polypeptide that comprises the extracellular N-terminal domain of the human thrombin receptor, a transmembrane protease-activated receptor (PAR-1). Gel filtration and fluorescence analysis showed that the fluorescent lipopolypeptide spontaneously inserted into preformed phospholipid vesicles, but it did not insert into whole cell membranes. In contrast, the dipalmitoyl derivative could only be reconstituted into artificial membranes by mixing the lipopolypeptide and phospholipid before vesicle formation. These results suggest that biophysical interactions governing the lipopolypeptide insertion into artificial and cellular membranes may differ. The thiol-reactive lipidating reagents should be valuable materials for studying the structure and function of peptides and polypeptides at phospholipid bilayer surfaces.

Amino Acid Sequence↗

PubMed1992

Quantitation of lateral stress in lipid layer containing nonbilayer phase preferring lipids by frequency-domain fluorescence spectroscopy.

Frequency-resolved fluorescence measurements have been performed to quantitate the lateral stress of the lipid layer containing nonbilayer phase preferring dioleoylphosphatidylethanolamine (DOPE). On the basis of a new rotational diffusion model, the wobbling diffusion constant (Dw), the curvature-related hopping diffusion constant (DH), and the two local orientational order parameters ([P2] and [P4]) of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenyl]ethyl] carbonyl]-3-sn-phosphatidylcholine (DPH-PC) in fully hydrated DOPE and DOPE/dioleoylphosphatidylcholine (DOPC) mixtures were calculated from the frequency-domain anisotropy data. The values of [P2], [P4], and DH for DOPE were found to increase significantly at approximately 12 degrees C, the known lamellar liquid crystalline (L alpha) to inverted hexagonal (HII) phase transition temperature of DOPE. Similar features as well as a decline of Dw were detected in the DOPE/DOPC mixtures as the DOPE content was increased from 85% to 90% at 23 degrees C, corresponding to the known lyotropic phase transition of the DOPE/DOPC. In contrast, for DOPC (0-40 degrees C) and DOPE/DOPC (0-100% DOPE at 3 degrees C), which remained in the L alpha phase, these changes were not detected. The most probable local orientation of DPH-PC in the DOPE/DOPC mixtures shifted progressively toward the normal of the lipid/water interface as the content of DOPE increased. We concluded that the curvature-related lateral stress in the lipid layer increases with the content of the nonbilayer phase preferring lipids.

Diffusion↗

PubMed1992

Lateral diffusion and percolation in two-phase, two-component lipid bilayers. Topology of the solid-phase domains in-plane and across the lipid bilayer.

Fluorescence recovery after photobleaching (FRAP) has recently been used to examine the percolation properties of coexisting phases in two-component, two-phase phosphatidylcholine bilayers [Vaz, W. L. C., Melo, E. C. C., & Thompson, T. E. (1989) Biophys. J. 56, 869-876]. We now report the use of FRAP to study two additional problems in similar systems. The first is the effect of solid-phase obstacles on the lateral diffusion in the fluid phase. The second is the question of whether or not, in a single bilayer, solid-phase domains in one monolayer are exactly superimposed on solid domains in the apposing monolayer. To address the first problem, the lateral diffusion of N-(7-nitrobenzoxa-2,3-diazol-4-yl)-1-palmitoyl-2-oleoylphosp hatidylethanolamine (NBD-POPE), a probe soluble only in the fluid phase when solid and fluid phases coexist, has been studied in the mixture N-lignoceroyldihydrogalactosylceramide (LigGalCer)/dipalmitoylphosphatidylcholine (DPPC). Percolation of the fluid phase occurs at a high mass fraction of solid phase. This indicates that the solid domains have a centrosymmetric shape, a characteristic which makes this a good experimental system to test theoretical simulations of diffusion in an archipelago. It is shown that agreement between theory and experiment is poor, a result that had already been observed when the obstacles were integral membrane proteins. We develop an effective-medium model for diffusion in two-phase systems which explains both our results and those obtained with integral proteins. The distinctive feature of the model is the consideration of an annular region around the obstacles where the lipids are more ordered than in the bulk fluid phase. The diffusion coefficient is then calculated by extending the free area model to two-phase systems, taking these annuli into account. The second question, the organization of the solid-phase domains across the lipid bilayer, is examined in the systems LigGalCer/DPPC and dimyristoylphosphatidylcholine (DMPC)/distearoylphosphatidylcholine (DSPC) by comparing the diffusion of a fluid-phase-soluble, gel-phase-insoluble lipid derivative which spans the two monolayers of a bilayer (NBD-membrane-spanning-phosphatidylethanolamine, NBD-msPE) with that of a probe which is restricted to a single monolayer. In LigGalCer/DPPC, 20:80, the distribution of solid domains in one of the monolayers is independent of the distribution in the apposing monolayer. In contrast, in DMPC/DSPC, 50:50, the solid domains in one monolayer are exactly superimposed upon the solid domains existing in the apposing monolayer.

Diffusion↗

PubMed1986

Heterogeneity of lipid A: structural determination by 13C and 31P NMR of lipid A fractions from lipopolysaccharide of Escherichia coli 0111.

Purified lipid A from Escherichia coli 0111 was fractionated by thin-layer chromatography, and seven major bands were studied by 13C and 31P NMR. All lipid A fractions except one had fatty acids, 3-hydroxytetradecanoic acid, 3-(acyloxy)tetradecanoic acid, and phosphate groups bonded to the diglucosamine backbone. The remaining fraction was shown to be phosphatidylethanolamine. The number of substituents found showed that in all fractions all sites available for C-acylation (C-3, C-4, and C-3') and N-acylation (C-2 and C-2') carried acylic substituents. The number, ranging from four to six, and type of ester-bound carboxylic acid residues as well as the number of phosphate groups differed among the fractions. The three fastest moving bands all had three unsubstituted hydroxy fatty acids and one phosphate group (C-4'), while the slower moving bands had four hydroxy fatty acids and two phosphate groups. Unsubstituted 3-hydroxytetradecanoic acid residues were amide-bound to the disaccharide in all but one of the fractions. In summary, the heterogeneity of E. coli 0111 lipid A is found to be a consequence of a variation of the number and composition of carboxylic acid residues and of varying phosphate content.

Carbon↗

PubMed1988

Lipid-lipid interactions in reconstituted high-density lipoproteins by deuterium nuclear magnetic resonance.

Lipid-lipid interactions between the core and monolayer have been studied by using reconstituted high-density lipoproteins (rHDLs) composed of apoHDL3 with either dipalmitoylphosphatidylcholine (DPPC) or egg phosphatidylcholine (egg PC) as the monolayer and either cholesteryl oleate (CO) or triolein (TO) as the core. The effect of the monolayer on the core was observed by deuterium nuclear magnetic resonance (2H NMR) studies of rHDLs containing the core component cholesteryl [18, 18, 18-2H3] oleate [( 2H3]CO) or tri[16,16-2H2]oleoylglycerol [( 2H6]TO) surrounded by a monolayer of either DPPC or egg PC as a function of temperature. The reverse effect, that of the core on the monolayer, was examined by both 2H and 31P NMR studies of rHDLs containing [5,5-2H2]PC in the presence of CO or TO as a function of temperature. The 2H NMR line widths of [2H3]CO and [2H6]TO were considerably broader and showed a greater temperature dependence in rHDLs containing DPPC than in those containing egg PC. Similarly, the C-2H order parameters of [2H2]PC were higher and showed a greater temperature dependence in rHDLs containing CO than in those containing TO. In contrast, the 31P NMR line widths were identical for both [2H2]-PC/CO/apoHDL3 and [2H2]PC/TO/apoHDL3 at 25 and 6 degrees C, showing only a slight temperature dependence. Thus, acyl chains of both the monolayer and core components show increased order when in contact with neighboring lipids of higher order. The data demonstrate a direct effect of core cholesteryl esters and triglycerides with the phospholipid monolayer of HDL.

Deuterium↗

PubMed2005

Lipid mobility and molecular binding in fluid lipid membranes.

The lateral mobility of dilute concentrations of fluorescently labeled lipids doped into supported membranes is found to change upon receptor ligand binding at the membrane surface, even when the lipid is not directly involved in the binding event. Experiments using membrane microarrays are performed that illustrate the use of lipid mobility measurements as an effectively label-free strategy of detecting binding on membrane surfaces.

Animals↗

PubMed2000

Lipid oxidation in a chicken muscle model system: oxidative response of lipid classes to iron ascorbate or methemoglobin catalysis.

Catalysis by iron ascorbate and activated methemoglobin generated different oxidative responses in chicken muscle model systems. In iron ascorbate systems, large increases in hydroperoxides and thiobarbituric acid-reactive substances (TBARS) occurred during the initial stage of incubation. Thereafter, iron ascorbate catalysis led to a slow increase in the oxidation of triacylglcyerol (TG) and sarcoplasmic reticulum (SR) membrane lipids. By the end of incubation, 24, 36, and 32% of the initial content of n-3 fatty acids in free fatty acids, TG, and SR single-lipid model systems catalyzed by iron ascorbate had been lost. Reduced losses of n-3 fatty acids were observed in the SR and TG fractions (0 and 24%, respectively) when iron ascorbate model systems contained all three lipid fractions (mix). Hydroperoxides and TBARS in model systems catalyzed by activated methemoglobin were characterized by a lag phase during most of the incubation. Consistent with their role as antioxidants, losses of alpha-tocopherol (42-49%), gamma-tocopherol (36-42%), and protein sulfhydryls (41-52%) were observed in model systems catalyzed by activated methemoglobin. SR and mix model systems were 30-50% slower to oxidize than TG model systems when activated methemoglobin served as the catalytic agent.

Animals↗

PubMed1997

Cytotoxicity of solid lipid nanoparticles as a function of the lipid matrix and the surfactant.

PURPOSE: Assessment of the in vitro cytotoxicity of solid lipid nanoparticles (SLNs) as a function of lipid matrix (Dynasan 114, Compritol ATO 888), and stabilizing surfactant (poloxamers, Tween 80, soya lecithin, and sodium dodecyl sulphate). Comparison with other colloidal carriers should determine their potential use in the clinic. METHODS: SLNs were produced by high pressure homogenisation. Cytotoxicity was assessed by measuring the viability of HL60 cells and human granulocytes after incubation with SLNs. Particle internalisation was quantified by chemiluminescence measurements. RESULTS: The nature of the lipid had no effect on viability; distinct differences were found for the surfactants. Binding to the SLN surface reduced markedly the cytotoxic effect of the surfactants, e.g., up to a factor of 65 for poloxamer 184. The permanent HL60 cell line-differentiated from cells with granulocyte characteristics by retinoic acid treatment-yielded results identical to freshly isolated human granulocytes. In general, the SLNs showed a lower cytotoxicity compared to polyalkylcyanoacrylate and polylactic/glycolic acid (PLA/ GA) nanoparticles. CONCLUSIONS: Because the results are identical when using human granulocytes, differentiated HL60 cells can be used as an easily accessible in vitro test system for i.v. injectable SLN formulations. The SLNs appear suitable as a drug carrier system for potential intravenous use due to their very low cytotoxicity in vitro.

Cell Survival↗

PubMed2001

Serum lipid levels in an Iranian population of children and adolescents: Tehran lipid and glucose study.

Data from 3148 participants aged 3-19 years (1447 males and 1701 females) in the cross-sectional phase of Tehran lipid and glucose study (February 1999-May 2000) were used to determine serum lipid levels [total cholesterol (TC), triglycerides (TGs), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C)] after 12-14 hours overnight fast. The values were analyzed by sex and age. Mean serum TC concentration was 170 mg/dl. TC was significantly greater in females than males (173 vs. 167 mg/dl, p < 0.05). The 90th and 95th percentiles for serum TC were 211 and 227 mg/dl, respectively. There was a significant decrease in mean TC in males during puberty. Thirty-one percent of population had TC values between 170 and 199 mg/dl and 16% had values of 200 mg/dl or greater. The mean TGs values were 103 for males and 108 mg/dl for females [non-significant (NS)]. The prevalence of high-risk values of TGs increased with age in males, reaching a peak at 17-19 years. The mean HDL-C level was 45 mg/dl. Mean HDL-C was highest at 7-10 years of age and decreased thereafter. The mean LDL-C was 102 in males and 107 mg/dl in females (NS). Twenty-two percent had LDL-C values between 110 and 129 mg/dl and 17% had values 130 mg/dl or greater. The results showed higher levels of TC, LDL-C and TGs and lower HDL-C in Tehranian children and adolescents than other studies. To design comprehensive public health programs to reduce serum lipid levels among Iranian children and adolescents, underlying factors for the high prevalence of dyslipoproteinemia should be sought.

Adolescent↗

PubMed1997

Dietary practices and lipid intake in relation to plasma lipid profile in Hong Kong Chinese.

OBJECTIVE: To study dietary lipid intake and plasma lipid profile of the Hong Kong Chinese population as part of a territory wide survey on cardiovascular risk factors. DESIGN: Randomised age and sex stratified survey. SUBJECTS: 1010 subjects aged 25-74 y (500 men, 510 women). MEASUREMENTS: A food frequency method with food tables compiled for Hong Kong was used for nutrient quantitation, while a separate questionnaire was used to examine dietary practices. Plasma lipid profile was estimated using standard laboratory methods. RESULTS: Total calorie, fat, saturated fatty acid (SFA), poly- and mono-unsaturated fatty acid (PUFA and MUFA), and cholesterol intake were higher in men; however when adjusted for caloric intake no difference was observed. Men had lower intake of PUFA as percentage of total energy had a higher Hegsted Score compared with women. Subjects consuming beans twice or more per week had lower total cholesterol and LDL-cholesterol concentrations. Overall, the population dietary intake was close to the ideal for cardiovascular health: percentage fat not greater than 30% of the total calorie intake, saturated fat intake not greater than 10% of calories, and cholesterol less than 180 mg/1000 Kcal. CONCLUSION: The dietary pattern for Hong Kong Chinese appear to be satisfactory with respect to cardiovascular health.

Adult↗

PubMed1988

Dexamethasone influences the lipid fluidity, lipid composition and glycosphingolipid glycosyltransferase activities of rat proximal-small-intestinal Golgi membranes.

Experiments were performed to examine the effects of subcutaneous administration of the synthetic glucocorticoid dexamethasone (100 micrograms/day per 100 g body wt.) on the lipid fluidity, lipid composition and glycosphingolipid glycosyltransferase activities of rat proximal-small-intestinal Golgi membranes. After 4 days of treatment, Golgi membranes and liposomes prepared from treated rats were found to possess a greater fluidity than their control (diluent or 0.9% NaCl) counterpart, as assessed by steady-state fluorescence-polarization techniques using three different fluorophores. Moreover, analysis of the effects of temperature on the anisotropy values of 1,6-diphenylhexa-1,3,5-triene, using Arrhenius plots, demonstrated that the mean break-point temperatures of treated preparations were 4-5 degrees C lower than those of control preparations. Changes in the fatty acyl saturation index and double-bond index of treated membranes, secondary to alterations in stearic acid, linoleic acid and arachidonic acid, at least in part, appeared to be responsible for the differences in fluidity noted between treated and control Golgi membranes. Concomitant with these fluidity and lipid-compositional alterations, treated membranes possessed higher specific activities of UDP-galactosyl-lactosylceramide galactosyltransferase and CMP-N-acetylneuraminic acid:lactosylceramide sialyltransferase than their control counterparts. Experiments utilizing benzyl alcohol, a known fluidizer, furthermore suggested that the fluidity alteration induced by dexamethasone may be responsible for the increased activity of the former, but not the latter, glycosphingolipid glycosyltransferase.

Animals↗

PubMed1990

Relationship between lipid saturation and lipid-protein interaction in liver mitochondria modified by catalytic hydrogenation with reference to cardiolipin molecular species.

Lipid acyl double bonds in isolated mitochondrial membranes were gradually reduced by palladium-complex-catalysed hydrogenation, and the resulting saturation was monitored by fatty acid analysis of phosphatidylcholine, phosphatidylethanolamine and cardiolipin. The courses of hydrogenation of these phospholipids suggested that cardiolipin is in a membrane compartment which is less accessible to the applied catalyst. Native cardiolipin and its hydrogenation products were further characterized by analysis of their molecular diacylglycerol species. A decrease in the double bond content was accompanied by an increased amount of motionally restricted lipids at the hydrophobic interface of proteins as measured by two different spin-labelled lipids (C-14 positional isomers of spin-labelled stearic acid and phosphatidylcholine analogues). The protein-immobilized fraction of spin-labelled stearic acid increased in parallel with the hydrogenation of cardiolipin rather than of phosphatidylcholine or phosphatidylethanolamine. These data are interpreted in terms of a tight association of cardiolipin with membrane proteins, which becomes looser upon double bond reduction leading to the replacement of cardiolipin by spin-labelled stearic acid in the solvation shell. Thus the hydrophobic moiety of cardiolipin, characterized by double-unsaturated C18-C18 diacylglycerol species, seems to be an important structural requirement for the high protein affinity of this compound.

Animals↗

PubMed2000

Characterization of a novel lipid A containing D-galacturonic acid that replaces phosphate residues. The structure of the lipid a of the lipopolysaccharide from the hyperthermophilic bacterium Aquifex pyrophilus.

According to the 16 S rRNA phylogenetic tree, the hyperthermophilic bacterium Aquifex pyrophilus represents the deepest and shortest branching species of the kingdom Bacteria. We show for the first time that an organism, which is phylogenetically ancient on the basis of its 16 S rRNA and that exists at extreme conditions, may contain lipopolysaccharide (LPS). The LPS was extracted from dried bacteria using a modified phenol/water method. SDS-polyacrylamide gel electrophoresis and silver stain displayed a ladder-like pattern, which is typical for smooth-form LPS (possessing an O-specific polysaccharide). The molecular masses of the LPS populations were determined by matrix-assisted laser-desorption ionization mass spectrometry. Lipid A was precipitated after mild acid hydrolysis of LPS. Its complete structure was determined by chemical analyses, combined gas-liquid chromatography-mass spectrometry, matrix-assisted laser-desorption ionization mass spectrometry, and one- and two-dimensional NMR spectroscopy. The lipid A consists of a beta-(1-->6)-linked 2,3-diamino-2,3-dideoxy-D-glucopyranose (DAG) disaccharide carrying two residues each of (R)-3-hydroxytetradecanoic acid and (R)-3-hydroxyhexadecanoic acid in amide linkage and one residue of octadecanoic acid in ester linkage. Each DAG moiety carries one residue of each 3-hydroxytetradecanoic and 3-hydroxyhexadecanoic acid. In the nonreducing DAG, the octadecanoic acid is attached to the 3-hydroxy group of 3-hydroxytetradecanoic acid. Each DAG is substituted by one D-galacturonic acid residue, which is linked to O-1 of the reducing and to O-4 of the nonreducing end. This structure represents a novel type of lipid A.

Gram-Negative Aerobic Rods and Cocci↗

PubMed2006

Regulation of lipid metabolism genes, lipid carrier protein lipophorin, and its receptor during immune challenge in the mosquito Aedes aegypti.

In the mosquito Aedes aegypti, the expression of two fat body genes involved in lipid metabolism, a lipid carrier protein lipophorin (Lp) and its lipophorin receptor (LpRfb), was significantly increased after infections with Gram (+) bacteria and fungi, but not with Gram (-) bacteria. The expression of these genes was enhanced after the infection with Plasmodium gallinaceum. RNA interference (RNAi) knockdown of Lp strongly restricted the development of Plasmodium oocysts, reducing their number by 90%. In Vg-DeltaREL1-A transgenic mosquitoes, with gain-of-function phenotype of Toll/REL1 immune pathway activated after blood feeding, both the Lp and LpRfb genes were overexpressed independently of septic injury. The same phenotype was observed in the mosquitoes with RNAi knockdown of Cactus, an IkappaB inhibitor in the Toll/REL1 pathway. These results showed that, in the mosquito fat body, both Lp and LpRfb gene expression were regulated by the Toll/REL1 pathway during immune induction by pathogen and parasite infections. Indeed, the proximal region of the LpRfb promoter contained closely linked binding motifs for GATA and NF-kappaB transcription factors. Transfection and in vivo RNAi knockdown experiments showed that the bindings of both GATA and NF-kappaB transcription factors to the corresponding motif were required for the induction of the LpRfb gene. These findings suggest that lipid metabolism is involved in the mosquito systemic immune responses to pathogens and parasites.

Aedes↗

PubMed1983

Effect of high vitamin A or tocopherol intake on hepatic lipid metabolism and intestinal absorption and secretion of lipids and bile acids in the chick.

The effect of high dietary vitamin A or tocopherol, or both, on lipid absorption and secretion in the gastrointestinal tract and on serum and hepatic lipids was determined in the chick. High dietary vitamin A increased secretion of cholesterol, bile acids, phospholipids and fatty acids to the duodenum, and tocopherol enhanced cholesterol and bile acid secretion to the duodenum. No differences in over-all absorption were observed. Serum cholesterol was depressed by vitamin A and hepatic lipids were enhanced, except phosphatidyl choline which was depressed. Tocopherol increased hepatic triglycerides and cholesterol. In vitro fatty acid synthesis from lactate by liver homogenates was enhanced by vitamin E and cholesterogenesis enhanced by both vitamin A and tocopherol. delta 9 Desaturation was also enhanced by vitamin E. It is concluded that both vitamin A and tocopherol affect the hepatic synthesis and catabolism of cholesterol and that vitamin E also influences fatty acid metabolism.

Animals↗

PubMed1985

Reactions of proteins with oxidizing lipids. 1. Analytical measurements of lipid oxidation and of amino acid losses in a whey protein-methyl linolenate model system.

The reactions between protein-bound amino acids and oxidizing lipid were investigated in a whey protein-methyl linolenate (C18:3)-water model system. The extent of fat oxidation was followed by measuring oxygen uptake, hydroperoxide formation and hydrocarbon (ethane and pentane) formation. Significant losses occurred with lysine (up to 71%), tryptophan (up to 31%) and histidine (up to 57%). Methionine was extensively oxidized to its sulphoxide but less than 2% was further oxidized to the sulphone. No other amino acids were affected. Increasing storage temperature (20 degrees, 37 degrees, 55 degrees) resulted in an enhancement of fat oxidation reactions and amino acid degradation. Increasing water activity (0.28, 0.65, 0.90) increased losses of lysine and tryptophan but had no influence on the oxidation of methionine, the level of remaining hydroperoxides or O2 uptake. Hydrocarbons were decreased. Limitation of O2 uptake to 1 mol/mol lipid instead of excess O2 (O2 uptake about 2.5 mol/mol lipid in 4 weeks) significantly reduced the degradation of lysine and tryptophan but had less influence on the oxidation of methionine. The level of remaining hydroperoxides was increased but hydrocarbons were unaffected.

Amino Acids↗