Showing papers on "Fatty acid published in 1998"

Crystal structure of human serum albumin complexed with fatty acid reveals an asymmetric distribution of binding sites

Abstract: Human serum albumin (HSA) is the most abundant protein in the circulatory system. Its principal function is to transport fatty acids, but it is also capable of binding a great variety of metabolites and drugs. Despite intensive efforts, the detailed structural basis of fatty acid binding to HSA has remained elusive. We have now determined the crystal structure of HSA complexed with five molecules of myristate at 2.5 A resolution. The fatty acid molecules bind in long, hydrophobic pockets capped by polar side chains, many of which are basic. These pockets are distributed asymmetrically throughout the HSA molecule, despite its symmetrical repeating domain structure.

Impacts of Carbon and Flooding on Soil Microbial Communities: Phospholipid Fatty Acid Profiles and Substrate Utilization Patterns

Abstract: Phospholipid fatty acid (PLFA) profiles provide a robust measure that can be used to fingerprint the structure of soil microbial communities, and measure their biomass. A replicated field trial, with gradients in substrate and O2 availability created by straw incorporation and flooding was used to test the ability of PLFA to discriminate soil microbial communities in different management regimes. Another objective was to test the usefulness, on a large scale, of some of the proposed interpretations of PLFA biomarkers. Using a direct gradient statistical analysis method, PLFA profiles were found to be very sensitive to flooding and straw treatments. Relative abundances of monounsaturated fatty acids were reduced with flooding and increased with added carbon, consistent with their proposed interpretations as indicators of aerobic conditions and high substrate availability. The cyclopropyl fatty acids were not useful as taxonomic indicators of respiratory type, although their responses were consistent with their proposed use as growth condition indicators. Branched fatty acids decreased, as a group, in response to high substrate conditions. A specific biomarker for Type II methanotrophs was not found in this rice soil, even under high carbon, low O2 conditions, which resulted in methane exposure in the soil. Direct comparison of PLFA and substrate utilization patterns indicated that Biolog patterns are highly selective, and do not reflect compositional changes in soil communities.

Catalytic Plasticity of Fatty Acid Modification Enzymes Underlying Chemical Diversity of Plant Lipids

Abstract: Higher plants exhibit extensive diversity in the composition of seed storage fatty acids. This is largely due to the presence of various combinations of double or triple bonds and hydroxyl or epoxy groups, which are synthesized by a family of structurally similar enzymes. As few as four amino acid substitutions can convert an oleate 12-desaturase to a hydroxylase and as few as six result in conversion of a hydroxylase to a desaturase. These results illustrate how catalytic plasticity of these diiron enzymes has contributed to the evolution of the chemical diversity found in higher plants.

Desaturation and related modifications of fatty acids1

Abstract: ▪ Abstract Desaturation of a fatty acid first involves the enzymatic removal of a hydrogen from a methylene group in an acyl chain, a highly energy-demanding step that requires an activated oxygen intermediate. Two types of desaturases have been identified, one soluble and the other membrane-bound, that have different consensus motifs. Database searching for these motifs reveals that these enzymes belong to two distinct multifunctional classes, each of which includes desaturases, hydroxylases, and epoxidases that act on fatty acids or other substrates. The soluble class has a consensus motif consisting of carboxylates and histidines that coordinate an active site diiron cluster. The integral membrane class contains a different consensus motif composed of histidines. Biochemical and structural similarities between the integral membrane enzymes suggest that this class also uses a diiron cluster for catalysis. Soluble and membrane enzymes have been successfully re-engineered for substrate specificity and rea...

Regulatory interactions between lipids and carbohydrates: the glucose fatty acid cycle after 35 years

Abstract: Competition for respiration between substrates in animal tissues has been known for at least 80 years. The most important interaction, quantitatively is between glucose and fatty acids. The starting point in 1963 for the so called Glucose Fatty Acid Cycle was the realisation that the metabolic relationship between glucose and fatty acids is reciprocal and not dependent. Glucose provision promotes glucose oxidation and glucose and lipid storage, and inhibits fatty acid oxidation. Provision of free fatty acids promotes fatty acid oxidation and storage, inhibits glucose oxidation and may promote glucose storage if glycogen reserves are incomplete. This review is concerned predominantly with evidence in man in vivo. In the authors opinion the evidence for inhibitory effects of fatty acids on whole body glucose utilization ad oxidation (predominantly muscles) is decisive and enzyme mechanisms mediating these effects are well established. There is also much evidence that fatty acid oxidation inhibits glucose oxidation and stimulates glucose formation in liver and again enzyme mechanism are known. A permissive role for fatty acids in the insulin secretory response of islet beta-cells has now been firmly established and can be visualised as a mechanism to protect continuing provision of respiratory substrate. Longer term exposure of islet beta-cells to fatty acids impairs the insulin secretory response to glucose and mechanisms are known. There is compelling evidence that fatty acid oxidation may impair glucose oxidation in uncontrolled Type 1 and Type 2 diabetes, but no convincing evidence that fatty acids have a role in diminished glucose storage (glycogen deposition) in Type 2 diabetes. The inhibition of glucose storage which may follow prolonged elevation of plasma FFA in man and experimental animals is associated with glycogen repletion whereas the inhibition of glucose storage in Type 2 diabetes is associated with glycogen depletion. The precise role of fatty acids in disturbed carbohydrate metabolism in Type 2 diabetes is an area where future progress is confidently predicted.

Activation of cholesterol synthesis in preference to fatty acid synthesis in liver and adipose tissue of transgenic mice overproducing sterol regulatory element-binding protein-2.

Abstract: We produced transgenic mice that express a dominant-posi- tive truncated form of sterol regulatory element-binding protein-2 (SREBP-2) in liver and adipose tissue. The en- coded protein lacks the membrane-binding and COOH-ter- minal regulatory domains, and it is therefore not susceptible to negative regulation by cholesterol. Livers from the trans- genic mice showed increases in mRNAs encoding multi- ple enzymes of cholesterol biosynthesis, the LDL recep- tor, and fatty acid biosynthesis. The elevations in mRNA for 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) synthase and HMG CoA reductase were especially marked (13-fold and 75-fold, respectively). As a result, the trans- genic livers showed a 28-fold increase in the rate of choles- terol synthesis and a lesser fourfold increase in fatty acid synthesis, as measured by intraperitoneal injection of ( 3 H)water. These results contrast with previously reported effects of dominant-positive SREBP-1a, which activated fatty acid synthesis more than cholesterol synthesis. In adi- pose tissue of the SREBP-2 transgenics, the mRNAs for cholesterol biosynthetic enzymes were elevated, but the mRNAs for fatty acid biosynthetic enzymes were not. We conclude that SREBP-2 is a relatively selective activator of cholesterol synthesis, as opposed to fatty acid synthesis, in liver and adipose tissue of mice. ( J. Clin. Invest. 1998. 101: 2331-2339.) Key words: cholesterollow density lipoprotein • sterol regulatory element binding proteinsfatty acids • transgenic mice

Regulation of sterol regulatory element binding proteins in livers of fasted and refed mice

Abstract: Hepatic lipid synthesis is known to be regulated by food consumption. In rodents fasting decreases the synthesis of cholesterol as well as fatty acids. Refeeding a high carbohydrate/low fat diet enhances fatty acid synthesis by 5- to 20-fold above the fed state, whereas cholesterol synthesis returns only to the prefasted level. Sterol regulatory element binding proteins (SREBPs) are transcription factors that regulate genes involved in cholesterol and fatty acid synthesis. Here, we show that fasting markedly reduces the amounts of SREBP-1 and -2 in mouse liver nuclei, with corresponding decreases in the mRNAs for SREBP-activated target genes. Refeeding a high carbohydrate/low fat diet resulted in a 4- to 5-fold increase of nuclear SREBP-1 above nonfasted levels, whereas nuclear SREBP-2 protein returned only to the nonfasted level. The hepatic mRNAs for fatty acid biosynthetic enzymes increased 5- to 10-fold above nonfasted levels, a pattern that paralleled the changes in nuclear SREBP-1. The hepatic mRNAs for enzymes involved in cholesterol synthesis returned to the nonfasted level, closely following the pattern of nuclear SREBP-2 regulation. Transgenic mice that overproduce nuclear SREBP-1c failed to show the normal decrease in hepatic mRNA levels for cholesterol and fatty acid synthetic enzymes upon fasting. We conclude that SREBPs are regulated by food consumption in the mouse liver and that the decline in nuclear SREBP-1c upon fasting may explain in part the decrease in mRNAs encoding enzymes of the fatty acid biosynthetic pathway.

Validation of a Three-Stage Compound Continuous Culture System for Investigating the Effect of Retention Time on the Ecology and Metabolism of Bacteria in the Human Colon

Abstract: A three-stage compound continuous culture system was used to study the effect of retention time (27.1 and 66.7 h) on the catabolism of organic carbon and nitrogen sources in mixed populations of human colonic bacteria. The fermentation system was designed to reproduce spatial, temporal, nutritional, and physicochemical characteristics of the microbiota in the proximal (vessel 1) and distal (vessels 2 and 3) colons, and was validated on the basis of chemical and microbiological measurements on intestinal contents obtained from human sudden death victims. Results showed that the majority of carbohydrate breakdown and short-chain fatty acid production occurred in V1. Conversely, dissimilatory amino acid metabolism, as evidenced by formation of branched-chain fatty acids and phenolic compounds, occurred primarily in V2 and V3. Fermentation of aromatic amino acids was strongly affected by system retention time (R), with concentrations of phenolic metabolites being three times higher in V3, at 66.7 h, compared to 27.1 h. Bacteriological measurements of intestinal contents, in which nine groups of marker organisms were studied, showed that, with the exception of bifidobacteria, no major differences in relative bacterial cell numbers were evident in the proximal and distal colons. These organisms were also studied in the continuous culture system, where marked reductions in Escherichia coli were observed in V2 and V3, especially at R= 27.1 h. Increasing R to 66.7 h reduced numbers of Clostridium perfringens, anaerobic Gram-positive cocci, and total anaerobe counts. Correlations between in vivo chemical and bacteriological measurements and data obtained in vitro demonstrate that the three-stage fermentation system provided a useful model for studying the physiology and ecology of large intestinal microorganisms under different nutritional and environmental conditions.

A family of fatty acid transporters conserved from mycobacterium to man

Abstract: Long chain fatty acids (LCFAs) are an important source of energy for most organisms They also function as blood hormones, regulating key metabolic functions such as hepatic glucose production Although LCFAs can diffuse through the hydrophobic core of the plasma membrane into cells, this nonspecific transport cannot account for the high affinity and specific transport of LCFAs exhibited by cells such as cardiac muscle, hepatocytes, and adipocytes Transport of LCFAs across the plasma membrane is facilitated by fatty acid transport protein (FATP), a plasma membrane protein that increases LCFA uptake when expressed in cultured mammalian cells [Schaffer, J E & Lodish, H F (1994) Cell 79, 427–436] Here, we report the identification of four novel murine FATPs, one of which is expressed exclusively in liver and another only in liver and kidney Both genes increase fatty acid uptake when expressed in mammalian cells All five murine FATPs have homologues in humans in addition to a sixth FATP gene FATPs are found in such diverse organisms as Fugu rubripes, Caenorhabditis elegans, Drosophila melanogaster, Saccharomyces cerevisiae, and Mycobacterium tuberculosis The function of the FATP gene family is conserved throughout evolution as the C elegans and mycobacterial FATPs facilitate LCFA uptake when overexpressed in COS cells or Escherichia coli, respectively The identification of this evolutionary conserved fatty acid transporter family will allow us to gain a better understanding of the mechanisms whereby LCFAs traverse the lipid bilayer as well as yield insight into the control of energy homeostasis and its dysregulation in diseases such as diabetes and obesity

Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)?

Abstract: A diet including 2-3 portions of fatty fish per week, which corresponds to the intake of 1.25 g EPA (20:5n-3) + DHA (22:6n-3) per day, has been officially recommended on the basis of epidemiological findings showing a beneficial role of these n-3 long-chain PUFA in the prevention of cardiovascular and inflammatory diseases. The parent fatty acid ALA (18:3n-3), found in vegetable oils such as flaxseed or rapeseed oil, is used by the human organism partly as a source of energy, partly as a precursor of the metabolites, but the degree of conversion appears to be unreliable and restricted. More specifically, most studies in humans have shown that whereas a certain, though restricted, conversion of high doses of ALA to EPA occurs, conversion to DHA is severely restricted. The use of ALA labelled with radioisotopes suggested that with a background diet high in saturated fat conversion to long-chain metabolites is approximately 6% for EPA and 3.8% for DHA. With a diet rich in n-6 PUFA, conversion is reduced by 40 to 50%. It is thus reasonable to observe an n-6/n-3 PUFA ratio not exceeding 4-6. Restricted conversion to DHA may be critical since evidence has been increasing that this long-chain metabolite has an autonomous function, e.g. in the brain, retina and spermatozoa where it is the most prominent fatty acid. In neonates deficiency is associated with visual impairment, abnormalities in the electroretinogram and delayed cognitive development. In adults the potential role of DHA in neurological function still needs to be investigated in depth. Regarding cardiovascular risk factors DHA has been shown to reduce triglyceride concentrations. These findings indicate that future attention will have to focus on the adequate provision of DHA which can reliably be achieved only with the supply of the preformed long-chain metabolite.

A gender-related defect in lipid metabolism and glucose homeostasis in peroxisome proliferator- activated receptor alpha- deficient mice.

Abstract: The peroxisome proliferator-activated receptor alpha (PPARalpha) is a nuclear receptor implicated in the control of cellular lipid utilization. To test the hypothesis that PPARalpha is activated as a component of the cellular lipid homeostatic response, the expression of PPARalpha target genes was characterized in response to a perturbation in cellular lipid oxidative flux caused by pharmacologic inhibition of mitochondrial fatty acid import. Inhibition of fatty acid oxidative flux caused a feedback induction of PPARalpha target genes encoding fatty acid oxidation enzymes in liver and heart. In mice lacking PPARalpha (PPARalpha-/-), inhibition of cellular fatty acid flux caused massive hepatic and cardiac lipid accumulation, hypoglycemia, and death in 100% of male, but only 25% of female PPARalpha-/- mice. The metabolic phenotype of male PPARalpha-/- mice was rescued by a 2-wk pretreatment with beta-estradiol. These results demonstrate a pivotal role for PPARalpha in lipid and glucose homeostasis in vivo and implicate estrogen signaling pathways in the regulation of cardiac and hepatic lipid metabolism.

The effects of catalyst, free fatty acids, and water

Abstract: Transesterification of beef tallow and methanol is affected by many factors. Catalyst, free fatty acids, and water in beef tallow, and reaction time were investigated. Sodium hydroxide (NUOH) was a more effective catalyst than sodium methoxide (NaMeOj. NaOH and NaMeO reached their maximum activities at 0.3% and 0.5%, w/w of beef tallow, respectively. The presence of water had more negative effect on transesterification than did the presence of free fatty acids (FFA). For best results, the water content of beef tallow should be kept not beyond 0.0696, w/w. FFA content of beef tallow should be kept below 0.596, w/w. The transesterification of beef tallow was very slow in the first minute. The production of beef tallow methyl esters (BTME) was complete after about 15 min. There were still some mono- and diglycerides in the BTME phase after the reaction was finished. Keywords. Biodiesel, Transesterification, Beef tallow^. iodiesel, an alternative diesel fuel, is made from renewable biological sources such as vegetable oils and animal fats. It is biodegradable and nontoxic, and has low emission profiles compared to petroleum diesel (Krawczyk, 1996). Fatty acid methyl esters (FAME) can be used as biodiesel fuel or can

Optimization of docosahexaenoic acid production by Schizochytrium limacinum SR21

Abstract: Culture conditions of Schizochytrium limacinum SR21 for the purpose of microbial docosahexaenoic acid (DHA) production were investigated. The strain SR21 showed a wide tolerance to salinity; that is, the optimum salinity was between 50% and 200% that of sea water. Monosaccharides (glucose and fructose) and glycerol supported good cell growth and DHA yield. Di- and polysaccharides, oleic acid, and linseed oil gave low DHA yields. A high content of DHA (more than 30% of total fatty acids) was obtained from culture on glucose, fructose, and glycerol, and also the strain had simple polyunsaturated fatty acid profiles. The major polyunsaturated fatty acids other than DHA were n-6 docosapentaenoic acid only, and the contents of icosapentaenoic acid and arachidonic acid were less than 1%. Using corn steep liquor as a nitrogen source, a high total fatty acid content was obtained. The total fatty acid content in the dry cell weight increased as the concentration of the nitrogen source decreased, reached more than 50%. An increase in carbon source concentration led to a high DHA yield. A maximum DHA yield of more than 4 g/l was obtained in both glucose and glycerol media at 9% and 12% respectively. S. limacinum SR21 was thought to be a promising resource for microbial DHA production yielding a good level of productivity as well as a simple polyunsaturated fatty acid profile.

Rapid simultaneous lipid extraction and transesterification for fatty acid analyses

Abstract: An improved adaptation of the direct transesterification method of Lepage and Roy (J. Lipid Res. 25, 1391–96, 1984) for the preparation of fatty acid methyl esters allows notable saving of time and reagents. The material being analysed is heated for 10 minutes with methanol, acetyl chloride and hexane. © Rapid Science Ltd. 1998

Elevated Free Fatty Acids Induce Uncoupling Protein 3 Expression in Muscle: A Potential Explanation for the Effect of Fasting

Abstract: The newly described uncoupling protein 3 (UCP3) may make an important contribution to thermogenesis in humans because of its high level of expression in skeletal muscle. Contrary to expectations, fasting, a condition that reduces resting energy expenditure, has been reported to increase UCP3 expression in muscle. We have confirmed that a 10-fold increase in UCP3 mRNA levels occurs in rat quadriceps muscle between 12 and 24 h of food removal. A less consistent twofold increase in muscle UCP2 mRNA levels was observed in animals fasted for up to 72 h. Administration of recombinant leptin to prevent a fall in circulating leptin levels did not eliminate the fasting-induced increase in quadriceps UCP3 expression. Administration of a high dose of glucocorticoid to fed animals to mimic the increase in corticosterone induced by fasting did not reproduce the increase in UCP3 expression observed in fasted animals. In contrast, elevation of circulating free fatty acid levels in fed animals by Intralipid plus heparin infusion caused significant increases in the UCP3/actin mRNA ratio compared with saline-infused fed controls in both extensor digitorum longus (2.01 +/- 0.34 vs. 0.68 +/- 0.11, P = 0.002) and soleus muscles (0.31 +/- 0.07 vs. 0.09 +/- 0.02, P = 0.014). We conclude that free fatty acids are a potential mediator of the increase in muscle UCP3 expression that occurs during fasting. This seemingly paradoxical induction of UCP3 may be linked to the use of free fatty acid as a fuel rather than an increased need of the organism to dissipate energy.

Polyunsaturated fatty acid regulation of gene expression.

Abstract: For the past three decades, polyunsaturated fatty acids (PUFA) have been recognized as important energy sources and membrane components. PUFA also play key roles in many cellular events, such as gene regulation. Most recently, research has focused on identifying the mechanisms by which PUFA modulate gene transcription, mRNA stability and cellular differentiation. It is the purpose of this review to examine the effects of PUFA on gene expression in lipogenic as well as other tissues. Because the (n-3) and (n-6) series of PUFA are intimately involved in gene regulation, they will be the focus of review. The effects of other fatty acid families on gene expression are reviewed elsewhere.

Nutritional and hormonal regulation of enzymes in fat synthesis: studies of fatty acid synthase and mitochondrial glycerol-3-phosphate acyltransferase gene transcription.

Abstract: ▪ Abstract The activities of critical enzymes in fatty acid and triacylglycerol biosynthesis are tightly controlled by different nutritional, hormonal, and developmental conditions. Feeding previously fasted animals high-carbohydrate, low-fat diets causes a dramatic induction of enzymes—such as fatty acid synthase (FAS) and mitochondrial glycerol-3-phosphate acyltransferase (GPAT)—involved in fatty acid and triacylglycerol synthesis. During fasting and refeeding, transcription of these two enzymes is coordinately regulated by nutrients and hormones, such as glucose, insulin, glucagon, glucocorticoids, and thyroid hormone. Insulin stimulates transcription of the FAS and mitochondrial GPAT genes, and glucagon antagonizes the insulin effect through the cis-acting elements within the promoters and their bound trans-acting factors. This review discusses advances made in the understanding of the transcriptional regulation of FAS and mitochondrial GPAT genes, with emphasis on elucidation of the mechanisms by whi...

2,4-dichlorophenoxybutyric acid-resistant mutants of arabidopsis have defects in glyoxysomal fatty acid beta -oxidation

Abstract: It has been demonstrated previously that 2,4-dichlorophenoxybutyric acid (2,4-DB) is metabolized to produce a herbicide, 2,4-D, by the action of peroxisomal fatty acid beta-oxidation in higher plants. To isolate mutants that have defects in peroxisomal fatty acid beta-oxidation, we screened mutant lines of Arabidopsis seedlings for growth in the presence of toxic levels of 2,4-DB. Twelve of the mutants survived; of these, four required sucrose for postgerminative growth. This result suggests that these mutants have defects in peroxisomal fatty acid beta-oxidation, because peroxisomal fatty acid beta-oxidation plays an important role in producing sucrose from storage lipids during germination. Genetic analysis revealed that these mutants can be classified as carrying alleles at three independent loci, which we designated ped1, ped2, and ped3, respectively (where ped stands for peroxisome defective). The ped1 mutant lacks the thiolase protein, an enzyme involved in fatty acid beta-oxidation during germination and subsequent seedling growth, whereas the ped2 mutant has a defect in the intracellular transport of thiolase from the cytosol to glyoxysomes. Etiolated cotyledons of both ped1 and ped2 mutants have glyoxysomes with abnormal morphology.