Fatty Acid Composition of the Complex Lipids of Staphylococcus aureus During the Formation of the Membrane-bound Electron Transport System

In Staphylococcus aureus, 64 fatty acids could be separated by gas-liquid chromatography. The fatty acids consisted of normal, iso, and anteiso saturated fatty acids of from 10 to 21 carbon atoms. Of the total fatty acids, 2 to 4% were normal, iso, and anteiso monoenoic fatty acids. Positional isomers of the normal monoenoic fatty acids could be detected. The fatty acids could be extracted, leaving 1 to 2% of the total fatty acids in the residue. The proportions of the fatty acids in the residue and the total lipids differed significantly. The lipid extract contained less than 0.12% free fatty acid. Between 5 and 10% of the lipid fatty acids were associated with neutral lipids. The majority of the fatty acids were associated with the complex lipids: mono- and diglucosyl diglyceride, phosphatidyl glycerol, lysyl phosphatidyl glycerol, and cardiolipin. The proportions of the fatty acids changed markedly between bacteria grown anaerobically (no membrane-bound electron transport system) and those grown aerobically (containing a functional electron transport system). In each of the complex lipids, the proportions of the fatty acids, as well as the magnitude and direction of change in the molar quantity of the fatty acids per bacterium, changed dramatically between these growth conditions. Since the glucosyl diglycerides and phospholipids were formed from the same pool of diglyceride intermediates, the marked differences in fatty acids indicate that acyl transferase activities must be an important part of complex lipid metabolism in S. aureus.     

Indentification and Localization of the Fatty Acids in Haemophilus parainfluenzae

Haemophilus parainfluenzae was capable of synthesizing 22 fatty acids. These fatty acids were equivalent to 4% of the bacterial dry weight. These fatty acids were localized in the membrane-wall complex, which contained the respiratory pigments, the quinone, and the phospholipids. The fatty acids which could be extracted with organic solvents comprised 86% of the total fatty acids of the cell. These fatty acids were distributed as 98% in the phospholipids and 1.9% in the neutral lipids, of which 0.5% were free fatty acids. Palmitic, palmitoleic, oleic, and vaccenic acids comprised 72% of the total fatty acids and were found almost exclusively in the phospholipids. The phospholipids also contained the cyclopropane fatty acids. The neutral lipids contained significant proportions of the odd-numbered branched and straight-chain fatty acids. The principal free fatty acids were n-dodecanoic and pentadecenoic acids. The nonextractable wall complex contained 14% of the total fatty acids. These wall fatty acids were rendered soluble only after saponification. The wall fraction contained all of the beta-hydroxymyristic acid and most of the myristoleic and pentadecenoic acids. The significance of the distribution of fatty acids between nonesterified, neutral lipid, phospholipid, and nonextractible wall remains to be determined.     

植物脂肪酸的生物合成与基因工程

植物脂肪酸既具重要生理功能,又有巨大食用和工业价值。其生物合成途径较为复杂,涉及乙酰_CoA羧化酶、脂肪酸合成酶、脂肪酸去饱和酶和脂肪酸延长酶等一系列酶。近年来,对脂肪酸生物合成途径进行了大量研究,克隆出许多相关基因,初步阐明了脂肪酸合成规律,并在此基础上开展了利用基因工程技术调控脂肪酸合成研究,取得可喜进展。本文详细介绍了植物饱和脂肪酸、不饱和脂肪酸和超长链脂肪酸的生物合成与基因工程研究的新结果。     

植物脂肪酸的生物合成与基因工程

植物脂肪酸既具重要生理功能,又有巨大食用和工业价值。其生物合成途径较为复杂,涉及乙酰－ＣｏＡ羟化酶、脂肪酸合成酶、脂肪酸去饱和酶和脂肪酸延长酶等一系列酶。近年来,对脂肪酸生物合成途径进行了大量研究,克隆出许多相关基因,初步阐明了脂肪酸合成规律,并在此基础上开展了利用基因工程技术调控脂肪酸合成研究,取得可喜进展。本文详细介绍了植物饱和脂肪酸、不饱和脂肪酸和超长链脂肪酸的生物合成与基因工程研究的新结果     

Inhibition of ion permeability control properties of acetylcholine receptor from Torpedo californica by long-chain fatty acids

The characteristics of fatty acid inhibition of acetylcholine receptor function were examined in membrane vesicles prepared from Torpedo californica electroplax. Inhibition of the carbamylcholine-induced increase in sodium ion permeability was correlated with the bulk melting point of exogenously incorporated fatty acids. Above its melting temperature, a fatty acid could inhibit the large increase in cation permeability normally elicited by agonist binding to receptor. Below its melting temperature, a fatty acid was ineffective. None of the fatty acids altered any of the ligand binding properties of the receptor. Inhibitory fatty acids did not induce changes in membrane fluidity, as determined by electron paramagnetic resonance using spin-labeled fatty acids. The spin-labeled fatty acids also acted as inhibitors, and the extent of inhibition depended largely on the position of the nitroxide group along the fatty acid chain. Addition of noninhibitory fatty acid to the vesicle membranes did not protect the receptor from inhibition by spin-labeled fatty acids. The effects of free fatty acids on acetylcholine receptor function are attributed to the disruptions of protein-lipid interactions.     

Stimulation of the Ca2+-dependent polymerization of synexin by cis-unsaturated fatty acids

The influence of fatty acids on the polymerization of synexin was studied by monitoring light scattered from solutions of purified synexin. Cis-unsaturated fatty acids such as arachidonate or oleate stimulated synexin polymerization at sub-micromolar concentrations, while saturated fatty acids, a trans unsaturated fatty acid or a fatty acid methyl ester had little effect. The polymerization of synexin occurred at lower concentrations of Ca2+ in the presence of the fatty acids than in the absence of fatty acids. Therefore, Ca2+ and free fatty acids may act as co-regulators of synexin action in stimulated secretory cells.     

Biogenesis of mitochondria. The effects of altered membrane lipid composition on cation transport by mitochondria of Saccharomyces cerevisiae

1. The fatty acid composition of the membrane lipids of a fatty acid desaturase mutant of Saccharomyces cerevisiae was manipulated by growing the organism in a medium containing defined fatty acid supplements. 2. Mitochondria were obtained whose fatty acids contain between 20% and 80% unsaturated fatty acids. 3. Mitochondria with high proportions of unsaturated fatty acids in their lipids have coupled oxidative phosphorylation with normal P/O ratios, accumulate K(+) ions in the presence of valinomycin and an energy source, and eject protons in an energy-dependent fashion. 4. If the unsaturated fatty acid content of the mitochondrial fatty acids is lowered to 20%, the mitochondria simultaneously lose active cation transport and the ability to couple phosphorylation to respiration. 5. The loss of energy-linked reactions is accompanied by an increased passive permeability of the mitochondria to protons. 6. Free fatty acids uncouple oxidative phosphorylation in yeast mitochondria and the effect is reversed by bovine serum albumin. 7. The free fatty acid contents of yeast mitochondria are unaffected by depletion of unsaturated fatty acids, and free fatty acids are not responsible for the uncoupling of oxidative phosphorylation in organelles depleted in unsaturated fatty acids. 8. It is suggested that the loss of energy-linked reactions in yeast mitochondria that are depleted in unsaturated fatty acids is a consequence of the increased passive permeability to protons, and is caused by a change in the physical properties of the lipid phase of the inner mitochondrial membrane.     

斑点叉尾鮰鱼油脂成分分析

采用铁锅炼制提取斑点叉尾鮰内脏鱼油,然后加酸使其甲酯化,以气相色谱/质谱法分析鱼油中的脂肪酸.结果斑点叉尾鮰内脏纯油脂中鱼油达到99%.从鱼油中共鉴定出15种成分,有饱和脂肪酸及不饱和脂肪酸,还有少量烷烃类物质.不饱和脂肪酸含量为76.40%,其中多不饱和脂肪酸为18.03%,以C18∶ 2(16.23%)为主,单不饱和脂肪酸为58.37%,以C18∶ 1(54.88%)为主.饱和脂肪酸含量为20.91%,主要有C16∶ 0 (15.84%)和C18∶ 0(4.29%),多是低于C18以上的中长链脂肪酸.因此斑点叉尾鮰油脂可作功能性脂肪酸的重要膳食来源.     

Lipoidal Components of Bacterial Lipopolysaccharides: Nature and Distribution of Fatty Acids in Aerobacter aerogenes

The fatty acid distribution of Aerobacter aerogenes was studied by comparing the fatty acid composition of the lipoidal component of the endotoxin (lipid A) with the fatty acids of the readily extractable native lipids and total cellular fatty acids. The results for total cellular fatty acids and readily extractable native lipids were generally similar, but both quantitative and qualitative differences exist. In addition, profound differences between these two fractions and lipid A were observed. These differences included fewer fatty acids and lower concentrations of unsaturated and cyclopropane fatty acids in the lipid A. Hydroxy fatty acids persisted in the lipid A. The significance of these differences with respect to mammalian toxicity of endotoxins is discussed.     

Alterations of the composition and size of the free fatty acid pool of Tetrahymena responding to low-temperature stress

Cells of Tetrahymena mimbres (formerly T. pyriformis NT-1) in midlogarithmic growth under isothermal conditions (at 39 degrees C) contained a very small, compositionally discrete pool of free fatty acids, principally (60.6% of the total free fatty acid mass) palmitic and stearic acids. The composition, degree of unsaturation, and size of this free fatty acid pool were rapidly (15 min or less) altered in response to chilling. During the acclimation period following chilling to 15 degrees C, the size of the free fatty acid pool increased from a mean value of 15.5 nmol free fatty acid/mumol lipid phosphorus in 39 degrees C cells to 24.2 nmol free fatty acid/mumol lipid phosphorus. The degree of free fatty acid saturation rapidly increased over the initial hour following the onset of hypothermal conditions, but by 24 h the unsaturated free fatty acid/saturated free fatty acid ratio was 0.35 (equivalent to a 2.7-fold increase in unsaturation relative to 39 degrees C controls (unsaturated/saturated ratio = 0.13) and 4.4-fold greater than cells acclimated for 1 h (unsaturated/saturated ratio = 0.08)). By 24 h the percentage of palmitic and stearic acids had decreased to 45.6%. Similar, and in some instances more pronounced, changes were observed to occur in triacylglycerol-bound fatty acids. Modulation of steady-state free fatty acid composition could also be achieved by the addition of exogenous fatty acids to the growth medium. The ability to manipulate the level of intracellular free fatty acids should prove to be a valuable experimental tool in determining how specific fatty acids regulate various lipid-modifying enzymes.     

Temperature- and growth-phase-regulated changes in lipid fatty acid structures of psychrotolerant groundwater Proteobacteria

Cellular fatty acid compositions of five psychrotolerant groundwater isolates representing alpha- and beta-Proteobacteria were studied at temperatures ranging from 8 to 25 degrees C. Unsaturation of straight-chain fatty acids was the most common response to decreasing temperature and was detected in four of the isolates. On solid media, decrease of temperature resulted in a decrease of cyclopropane fatty acids in beta-proteobacterial isolates. The formation of cyclopropane fatty acids depended, however, to a greater extent on the growth phase than the temperature and increased drastically as the cells entered stationary phase. The alpha-proteobacterial isolates contained a branched C(19:1) fatty acid. The formation of the branched C(19:1) increased during growth in the same way as the cyclopropane fatty acids in beta-proteobacterial strains, indicating possibly an analogous formation of the branched fatty acid by methylation of the 18:1 fatty acid. Sphingomonas sp. K6 possessed a novel temperature-induced modification of lipid fatty acids. As temperature decreased from 25 to 8 degrees C, the fatty acid composition shifted from predominantly even-carbon fatty acids to odd-carbon fatty acids. The results show completely different fatty acid modifications in two strains of the same genus Sphingomonas.     

Use of fatty acids for the assessment of zooplankton grazing on bacteria, protozoans and microalgae

1. The distribution of fatty acids in different groups of bacteria, ciliated protozoans and microalgae is reviewed emphasizing specific fatty acids like odd-branched fatty acids and ( n -3) polyunsaturated fatty acids.
2. Odd-branched fatty acids and ( n -6) fatty acids appear to be good indicators of zooplankton grazing on bacteria and ciliates when they are detected in microcrustacean triacylglycerols. We give several examples where these fatty acids may be used as markers. The value of ( n -3) fatty acids in describing zooplankton grazing on phytoplankton seems to be low.     

Composition of phospholipids and of phospholipid fatty acids and aldehydes in human red cells

Improved methods for lipid analysis that have been developed recently were employed to reevaluate the phospholipid composition, the fatty acid and fatty aldehyde composition of the total phospholipid, and the fatty acid composition of the individual phospholipids of normal human red cells. Thirty-three fatty acids and five fatty aldehydes were estimated and tentatively identified in the total phospholipid of normal human red cells. Additional minor components were evident. The major individual phospholipids were isolated by silicic acid thin-layer chromatography and quantified. The fatty acid compositions of phosphatidyl ethanolamine, phosphatidyl serine, lecithin, and sphingomyelin were determined. Each of these phospholipids showed a distinctive and characteristic fatty acid pattern.     

Control of Fatty Acid Synthesis in Bacteria

When glycerol-requiring auxotrophs of Bacillus subtilis are deprived of glycerol, the synthesis of fatty acids continues at an apparent rate of 20 to 50% that of supplemented cultures. The newly synthesized fatty acids are not incorporated into phospholipid and accumulate as free fatty acids. These molecules undergo a much more rapid turnover than phospholipid fatty acids, and the rate of turnover is sufficient to indicate that the rate of fatty acid synthesis in glycerol-deprived cultures is similar to that in supplemented ones. The average chain length of the free fatty acids is greater than that of the phospholipid fatty acids. Cells deprived of required amino acids also show a diminution in the apparent rate of fatty acid synthesis; however, in this case, the fatty acids accumulate in phospholipid, and no increase of the free fatty acid fraction is observed. It is argued on the basis of these findings that the control of lipid synthesis does not operate at the level of transacylation but must act on one or more of the reactions of the fatty acid synthetase.     

Stability of the fatty acid composition of actinomycetes

The stability of fatty acid composition of total extractable lipids was studied in Streptomyces cultures. The type of fatty acid composition typical of the Streptomyces genus remains stable when the actinomycetes were grown as submerged cultures in various synthetic media: saturated fatty acids with methyl branching in the chain predominated in all of the cases, and fatty acids with an uneven number of carbon atoms in the chain prevailed in most of the cases. Fatty acids with the anteiso structure predominated among the acids with a branched chain, amounting to more than a half of the latter and reaching sometimes 50% of the total fatty acid content. Methyl branchings were located in the anteiso position in fatty acids with an uneven number of carbon atoms, and in the iso position in fatty acids with an even number of carbons. Unsaturated fatty acids were found as a minor component.     

Potential for daily supplementation of n-3 fatty acids to reverse symptoms of dry eye in mice

The purpose of this study was to determine the change in tear volume, as a predominant symptom of dry eye syndrome, in dietary n-3 fatty acid deficient mice compared with n-3 fatty acid adequate mice. The tear volume in n-3 fatty acid deficient mice was significantly lower than that in n-3 fatty acid adequate mice. In addition, the concentration of n-3 fatty acid in the lacrimal and meibomian glands, which affects the production of tears, was markedly decreased compared with n-3 fatty acid adequate mice. However, the tear volume recovered almost completely after one week of continuous administration of fish oil containing EPA and DHA in n-3 fatty acid deficient mice. Also, the concentration of DHA in the meibomian gland of n-3 fatty acid deficient group recovered to approximately 80% more than that of n-3 fatty acid adequate group. These results suggested that dietary n-3 fatty acids deficiency showed reversible dry eye syndrome, and that n-3 fatty acids have an important role in the production of tears.     

Inhibition of yeast phosphatidic-acid synthesis by free fatty acids

Particulate preparations obtained from cells of yeast Saccharomyces sake have been shown to possess glycerolphosphate acyltransferase and 1-acylglycerolphosphate acyltransferase activities. Glycerolphosphate acyltransferase exhibits a high specificity for saturated and monoenoic fatty acyl-CoA thioesters. When palmitoyl-CoA is employed as sole acyl group donor, the major lipid product is lysophosphatidic acid. 1-Acylglycerolphosphate acyltransferase of this yeast species has a rather strict specificity for monoenoic fatty acyl-CoA thioesters as acyl donor. These two acyltransferases are strongly inhibited in vitro by low concentrations of free fatty acids. 1-Acylglycerolphosphate acyltransferase is much more susceptible to fatty acid inhibition than glycerolphosphate acyltransferase. The inhibition is dependent not only on the concentration of fatty acid, but also on the length of exposure to fatty acid. Both saturated and unsaturated fatty acids inhibit the acyltransferase activities. The inhibitory effects of fatty acids cannot be ascribed to a nonspecific surfactant action of fatty acids. The present results support the view that free fatty acid serves as a regulator of glycerolipid synthesis.     

Essential fatty acid uptake and esterification in primary culture of rat hepatocytes

Primary cultures of adult rat hepatocytes were used to compare the uptake and esterification of essential polyunsaturated fatty acids (18:2, 20:3 and 20:4 of the n-6 series) with those of palmitic and oleic acids. The uptake of unesterified fatty acids was linearly related to the free fatty acid/albumin molar ratio for 14 h and did not depend on the unbound free fatty acid level. Whatever the initial free fatty acid/albumin molar ratio, it dropped to 0.5 +/- 0.1 mM after 14 h, thus showing that hepatocytes have a high capacity for clearing free fatty acids from the medium at high free fatty acid/albumin molar ratios. The free fatty acid uptake become saturable when the free fatty acid and albumin concentrations were raised and the free fatty acid/albumin ratio remained constant. This strongly suggests that albumin-hepatocyte interaction mediates free fatty acid uptake. This uptake was identical whatever the fatty acid tested and did not depend on the relative amounts of fatty acids when they were added simultaneously. Triacylglycerol accumulation and synthesis, monitored by labelled fatty acids, were related to the free fatty acid/albumin molar ratio and exhibited no specificity for the series of fatty acids tested. Triacylglycerols were enriched in all the fatty acids tested by up to 60%, and fatty acid incorporation into diacylglycerols and triacylglycerols reflected the free fatty acid composition of the medium. By contrast, neither the level nor the synthesis of phospholipids varied with free fatty acid/albumin, but the rate of phospholipid turnover depended on the fatty acids tested. Accumulation of these acids was smaller in phospholipids than in triacylglycerols. When linoleic and arachidonic acids were added together, phospholipids (especially phosphatidylethanolamine and phosphatidylinositol) were more enriched in arachidonic acid than triacylglycerols. This might be due to the specificity for fatty acid of the enzymes involved in phospholipid metabolism.     

Cellular fatty acid uptake: the contribution of metabolism

PURPOSE OF REVIEW: The aim of this review is to highlight the importance of fatty acid metabolism as a major determinant in fatty acid uptake. In particular, we emphasize how the activation, intracellular transport and downstream metabolism of fatty acids influence their uptake into cells. RECENT FINDINGS: Studies examining fatty acid entry into cells have focused primarily on the roles of plasma membrane proteins or the question of passive diffusion. Recent studies, however, strongly suggest that a driving force governing fatty acid uptake is the metabolic demand for fatty acids. Both gain and loss-of-function experiments indicate that fatty acid uptake can be modulated by activation at both the plasma membrane and internal sites, by intracellular fatty acid binding proteins, and by enzymes in synthetic or degradative metabolic pathways. Although the mechanism is not known, it appears that converting fatty acids to acyl-CoAs and downstream metabolic intermediates increases cellular fatty acid uptake, probably by limiting efflux. SUMMARY: Altered fatty acid metabolism and the accumulation of triacylglycerol and lipid metabolites has been strongly associated with insulin resistance and diabetes, but we do not fully understand how the entry of fatty acids into cells is regulated. Future studies of cellular fatty acid uptake should consider the influence of fatty acid metabolism and the possible interactions between fatty acid metabolism or metabolites and fatty acid transport proteins.     

Thermal regulation of fatty acid synthetase from Brevibacterium ammoniagenes.

The fatty acid composition of Brevibacterium ammoniagenes was affected by the temperature of growth. As the growth temperature was lowered, the proportion of unsaturated fatty acids increased. The fatty acid synthetase obtained from B. ammoniagense produced oleic acid as well as saturated fatty acids. The ratio of unsaturated to saturated fatty acids synthesized by this enzyme in vitro was dependent on the temperature of the enzyme reaction but not on the growth temperature of B. ammoniagenes from which the enzyme was prepared. These results suggest that the changes of composition in cellular fatty acids reflect the temperature dependence of the fatty acid synthetase.