Mitochondrial Fatty Acid Synthesis Research Articles

An ancient genetic link between vertebrate mitochondrial fatty acid synthesis and RNA processing

In bacteria, functionally related gene products are often encoded by a common transcript. Such polycistronic transcripts are rare in eukaryotes. Here we isolated several clones from human cDNA libraries, which rescued the respiratory-deficient phenotype of a yeast mitochondrial 3-hydroxyacyl thioester dehydratase 2 (htd2) mutant strain. All complementing cDNAs were derived from the RPP14 transcript previously described to encode the RPP14 subunit of the human ribonuclease P (RNase P) complex. We identified a second, 3' open reading frame (ORF) on the RPP14 transcript encoding a protein showing similarity to known dehydratases and hydratase 2 enzymes. The protein was localized in mitochondria, and the recombinant enzyme exhibited (3R)-specific hydratase 2 activity. Based on our results, we named the protein human 3-hydroxyacyl-thioester dehydratase 2 (HsHTD2), which is involved in mitochondrial fatty acid synthesis. The bicistronic arrangement of RPP14 and HsHTD2, as well as the general exon structure of the gene, is conserved in vertebrates from fish to humans, indicating a genetic link conserved for 400 million years between RNA processing and mitochondrial fatty acid synthesis.

An ancient genetic link between mitochondrial fatty acid synthesis and RNA processing

An ancient genetic link between mitochondrial fatty acid synthesis and RNA processing

Structure and function of human PPTase: implications from ternary complexes

Themodification of invariant Ser residues in acyl carrier proteins (ACPs) by transfer of a 4-phosphopantetheinemoiety is essential to all living organisms. The reactions is carried out by a diverse group of enzymes collectively characterized as 4-phosphopantetheine transferases (PPTases), also known as holo-ACP synthases, yielding holo-carrier proteins by group transfer of the 4-phosphopantetheine moiety from coenzyme A (CoA) as donor substrate. Recent molecular cloning and biochemical characterization of human PPTase revealed that it is a cytosolic, monomeric enzyme with broad acceptor substrate specificity, and requires Mg for catalysis. In order to better understand its mode of action, human PPTase was crystallised and structures of the enzyme, its complex with CoA, and in complex with CoA and cytosolic fatty acid synthase (FAS) ACP were determined. The enzyme, which adopts the same fold observed in bacterial group II PPTases, consists of two nearly identical domains with the active site located in a deep cleft between the domains. ACP binds with its essential Ser pointing towards the bound CoA, interacts with the enzyme on a large surface and is positioned primarily by hydrophobic forces. CoA-binding is mediated by a Mg ion complexed by Glu residues. Mutagenesis studies indicate that in addition to the residues involved in Mg-binding, a base catalyst Lys and a His are essential for catalysis. Although the shape of FASACP is complementary to the large basin on the enzyme near the active site, there are still features on the binding surface not explained by the ternary complex. It is tempting to speculate that these regions play a role in binding mitochondrial ACP, since it has been demonstrated that human PPTase can activate ACP from the mitochondrial fatty acid synthesis machinery as well. Progress on establishing the structure of this complex will also be reported. m09.p04

Integration of transcriptomic and metabolic analyses for understanding the global responses of low-temperature winemaking fermentations

Wine produced at low temperature is often considered to have improved sensory qualities. To investigate the effects of temperature on winemaking, the expression patterns during the industrial fermentation process carried out at 13 degrees C and 25 degrees C were compared, and correlated with physiological and biochemical data, including viability, fermentation byproducts and lipid content of the cells. From a total of 535 ORFs that were significantly differentially expressed between the 13 degrees C and 25 degrees C fermentations, two significant transcription programmes were identified. A cold-stress response was expressed at the initial stage of the fermentation, and this was followed by a transcription pattern of upregulated genes concerned with the cell cycle, growth control and maintenance in the middle and late stages of the process at 13 degrees C with respect to 25 degrees C. These expression patterns were correlated with higher cell viability at low temperature. The other relevant transcriptomic difference was that several genes implicated in cytosolic fatty acid synthesis were downregulated, while those involved in mitochondrial short-chain fatty acid synthesis were upregulated in the fermentation process conducted at 13 degrees C with respect to that at 25 degrees C. These transcriptional changes were qualitatively correlated with improved resistance to ethanol and increased production of short-chain (C(4)-C(8)) fatty acids and their corresponding esters at 13 degrees C as compared to 25 degrees C. While this increase of ethyl esters may account in part for the improved sensory quality of wine fermented at 13 degrees C, it is still unclear how the esterification of the short-chain fatty acids takes place. On the basis of its strong upregulation at 13 degrees C, we propose a possible role of IAH1 encoding an esterase/ester synthase in this process.

Mitochondrial fatty acid synthesis and maintenance of respiratory competent mitochondria in yeast

Mitochondrial FAS (fatty acid synthesis) of type II is a widely conserved process in eukaryotic organisms, with particular importance for respiratory competence and mitochondrial morphology maintenance in Saccharomyces cerevisiae. The recent characterization of three missing enzymes completes the pathway. Etr1p (enoyl thioester reductase) was identified via purification of the protein followed by molecular cloning. To study the link between FAS and cell respiration further, we also created a yeast strain that has FabI enoyl-ACP (acyl-carrier protein) reductase gene from Escherichia coli engineered to carry a mitochondrial targeting sequence in the genome, replacing the endogenous ETR1 gene. This strain is respiratory competent, but unlike the ETR1 wild-type strain, it is sensitive to triclosan on media containing only non-fermentable carbon source. A colony-colour-sectoring screen was applied for cloning of YHR067w/RMD12, the gene encoding mitochondrial 3-hydroxyacyl-ACP dehydratase (Htd2/Yhr067p), the last missing component of the mitochondrial FAS. Finally, Hfa1p was shown to be the mitochondrial acetyl-CoA carboxylase.

Mitochondrial fatty acid synthesis and maintenance of respiratory competent mitochondria in yeast

Mitochondrial FAS (fatty acid synthesis) of type II is a widely conserved process in eukaryotic organisms, with particular importance for respiratory competence and mitochondrial morphology maintenance in Saccharomyces cerevisiae. The recent characterization of three missing enzymes completes the pathway. Etr1p (enoyl thioester reductase) was identified via purification of the protein followed by molecular cloning. To study the link between FAS and cell respiration further, we also created a yeast strain that has FabI enoyl-ACP (acyl-carrier protein) reductase gene from Escherichia coli engineered to carry a mitochondrial targeting sequence in the genome, replacing the endogenous ETR1 gene. This strain is respiratory competent, but unlike the ETR1 wild-type strain, it is sensitive to triclosan on media containing only non-fermentable carbon source. A colony-colour-sectoring screen was applied for cloning of YHR067w/RMD12, the gene encoding mitochondrial 3-hydroxyacyl-ACP dehydratase (Htd2/Yhr067p), the last missing component of the mitochondrial FAS. Finally, Hfa1p was shown to be the mitochondrial acetyl-CoA carboxylase.

Mitochondrial trans-2-Enoyl-CoA Reductase of Wax Ester Fermentation from Euglena gracilis Defines a New Family of Enzymes Involved in Lipid Synthesis

Under anaerobiosis, Euglena gracilis mitochondria perform a malonyl-CoA independent synthesis of fatty acids leading to accumulation of wax esters, which serve as the sink for electrons stemming from glycolytic ATP synthesis and pyruvate oxidation. An important enzyme of this unusual pathway is trans-2-enoyl-CoA reductase (EC 1.3.1.44), which catalyzes reduction of enoyl-CoA to acyl-CoA. Trans-2-enoyl-CoA reductase from Euglena was purified 1700-fold to electrophoretic homogeneity and was active with NADH and NADPH as the electron donor. The active enzyme is a monomer with molecular mass of 44 kDa. The amino acid sequence of tryptic peptides determined by electrospray ionization mass spectrometry were used to clone the corresponding cDNA, which encoded a polypeptide that, when expressed in Escherichia coli and purified by affinity chromatography, possessed trans-2-enoyl-CoA reductase activity close to that of the enzyme purified from Euglena. Trans-2-enoyl-CoA reductase activity is present in mitochondria and the mRNA is expressed under aerobic and anaerobic conditions. Using NADH, the recombinant enzyme accepted crotonyl-CoA (km=68 microm) and trans-2-hexenoyl-CoA (km=91 microm). In the crotonyl-CoA-dependent reaction, both NADH (km=109 microm) or NADPH (km=119 microm) were accepted, with 2-3-fold higher specific activities for NADH relative to NADPH. Trans-2-enoyl-CoA reductase homologues were not found among other eukaryotes, but are present as hypothetical reading frames of unknown function in sequenced genomes of many proteobacteria and a few Gram-positive eubacteria, where they occasionally occur next to genes involved in fatty acid and polyketide biosynthesis. Trans-2-enoyl-CoA reductase assigns a biochemical activity, NAD(P)H-dependent acyl-CoA synthesis from enoyl-CoA, to one member of this gene family of previously unknown function.

Structure of the mitochondrial β-ketoacyl-[acyl carrier protein] synthase from Arabidopsis and its role in fatty acid synthesis

Mitochondrial fatty acid synthesis is catalyzed by a dissociated fatty acid synthase similar to those of plant plastids and bacteria. The crystal structure of a mitochondrial β-ketoacyl-[acyl carrier protein] synthase (mtKAS), namely that from Arabidopsis thaliana, has been determined for the first time. This enzyme accomplishes the vital condensation steps in constructing fatty acid carbon skeletons. The product profile of mtKAS is unusual in that C 8 and C 14–16 fatty acyl chains predominate. An enzyme architecture that likely is the basis for the observed bimodal profile of mtKAS products can be derived from the shape of the acyl binding pocket.

Microbial type I fatty acid synthases (FAS): major players in a network of cellular FAS systems.

The present review focuses on microbial type I fatty acid synthases (FASs), demonstrating their structural and functional diversity. Depending on their origin and biochemical function, multifunctional type I FAS proteins form dimers or hexamers with characteristic organization of their catalytic domains. A single polypeptide may contain one or more sets of the eight FAS component functions. Alternatively, these functions may split up into two different and mutually complementing subunits. Targeted inactivation of the individual yeast FAS acylation sites allowed us to define their roles during the overall catalytic process. In particular, their pronounced negative cooperativity is presumed to coordinate the FAS initiation and chain elongation reactions. Expression of the unlinked genes, FAS1 and FAS2, is in part constitutive and in part subject to repression by the phospholipid precursors inositol and choline. The interplay of the involved regulatory proteins, Rap1, Reb1, Abf1, Ino2/Ino4, Opi1, Sin3 and TFIIB, has been elucidated in considerable detail. Balanced levels of subunits alpha and beta are ensured by an autoregulatory effect of FAS1 on FAS2 expression and by posttranslational degradation of excess FAS subunits. The functional specificity of type I FAS multienzymes usually requires the presence of multiple FAS systems within the same cell. De novo synthesis of long-chain fatty acids, mitochondrial fatty acid synthesis, acylation of certain secondary metabolites and coenzymes, fatty acid elongation, and the vast diversity of mycobacterial lipids each result from specific FAS activities. The microcompartmentalization of FAS activities in type I multienzymes may thus allow for both the controlled and concerted action of multiple FAS systems within the same cell.

Htd2p/Yhr067p is a yeast 3-hydroxyacyl-ACP dehydratase essential for mitochondrial function and morphology.

Among the recently recognized aspects of mitochondrial functions, in yeast as well as humans, is their ability to synthesize fatty acids in a malonyl-CoA dependent manner. We describe here the identification of the 3-hydroxyacyl-ACP dehydratase involved in mitochondrial fatty acid synthesis. A colony-colour-sectoring screen was applied in Saccharomyces cerevisiae in a search for mutants that, when grown on a non-fermentable carbon source, were unable to lose a plasmid that carried a chimeric construct coding for mitochondrially localized bacterial analogue. Our mutants, which are respiratory deficient, lack cytochromes and display abnormal mitochondrial morphology, were found to have a lesion in the yeast YHR067w/RMD12 gene. The Yhr067p is predicted to be a member of the thioesterase/thioester dehydratase-isomerase superfamily enzymes. Hydratase 2 activity in mitochondrial extracts from cells overexpressing YHR067w was increased. These overexpressing cells also display a striking mitochondrial enlargement phenotype. We conclude that YHR067w encodes a novel mitochondrial 3-hydroxyacyl-thioester dehydratase 2 and suggest renaming it HTD2. The mitochondrial phenotypes of the null and overexpression mutants suggest a crucial role of YHR067w in maintenance of mitochondrial respiratory competence and morphology in yeast.

Identification and Molecular Characterization of the β-Ketoacyl-[Acyl Carrier Protein] Synthase Component of the Arabidopsis Mitochondrial Fatty Acid Synthase

Substrate specificity of condensing enzymes is a predominant factor determining the nature of fatty acyl chains synthesized by type II fatty acid synthase (FAS) enzyme complexes composed of discrete enzymes. The gene (mtKAS) encoding the condensing enzyme, beta-ketoacyl-[acyl carrier protein] (ACP) synthase (KAS), constituent of the mitochondrial FAS was cloned from Arabidopsis thaliana, and its product was purified and characterized. The mtKAS cDNA complemented the KAS II defect in the E. coli CY244 strain mutated in both fabB and fabF encoding KAS I and KAS II, respectively, demonstrating its ability to catalyze the condensation reaction in fatty acid synthesis. In vitro assays using extracts of CY244 containing all E. coli FAS components, except that KAS I and II were replaced by mtKAS, gave C(4)-C(18) fatty acids exhibiting a bimodal distribution with peaks at C(8) and C(14)-C(16). Previously observed bimodal distributions obtained using mitochondrial extracts appear attributable to the mtKAS enzyme in the extracts. Although the mtKAS sequence is most similar to that of bacterial KAS IIs, sensitivity of mtKAS to the antibiotic cerulenin resembles that of E. coli KAS I. In the first or priming condensation reaction of de novo fatty acid synthesis, purified His-tagged mtKAS efficiently utilized malonyl-ACP, but not acetyl-CoA as primer substrate. Intracellular targeting using green fluorescent protein, Western blot, and deletion analyses identified an N-terminal signal conveying mtKAS into mitochondria. Thus, mtKAS with its broad chain length specificity accomplishes all condensation steps in mitochondrial fatty acid synthesis, whereas in plastids three KAS enzymes are required.

Structure–function Analysis of Enoyl Thioester Reductase Involved in Mitochondrial Maintenance

Candida tropicalis enoyl thioester reductase Etr1p and the Saccharomyces cerevisiae homologue Mrf1p catalyse the NADPH-dependent reduction of trans-2-enoyl thioesters in mitochondrial fatty acid synthesis (FAS). Unlike prokaryotic enoyl thioester reductases (ETRs), which belong to the short-chain dehydrogenases/reductases (SDR), Etr1p and Mrf1p represent structurally distinguishable ETRs that belong to the medium-chain dehydrogenases/reductases (MDR) superfamily, indicating independent origin of two separate classes of ETRs. The crystal structures of Etr1p, the Etr1p-NADPH complex and the Etr1Y79Np mutant were refined to 1.70 Å, 2.25 Å and 2.60 Å resolution, respectively. The native fold of Etr1p was maintained in Etr1Y79Np, but the mutant had only 0.1% of Etr1p catalytic activity remaining and failed to rescue the respiratory deficient phenotype of the mrf1Δ strain. Mutagenesis of Tyr73 in Mrf1p, corresponding to Tyr79 in Etr1p, produced similar results. Our data indicate that the mitochondrial reductase activity is indispensable for respiratory function in yeast, emphasizing the significance of Mrf1p (Etr1p) and mitochondrial FAS for the integrity of the respiratory competent organelle.

Pleiotropic phenotype of acetyl-CoA-carboxylase-defective yeast cells--viability of a BPL1-amber mutation depending on its readthrough by normal tRNA(Gln)(CAG).

The Saccharomyces cerevisiae gene BPL1 encodes the enzyme biotin:protein ligase (BPL), which is required for acetyl-CoA carboxylase (ACC) holoenzyme formation. Disruption of one of the two BPL1 alleles present in diploid cells results, upon sporulation, in a 2+:2(0) segregation of cell viability, with none of the two viable spores being BPL1 negative. In contrast to BPL1 deletants, BPL1 base-substitution mutants are potentially viable and may be isolated as long-chain-fatty-acid-requiring auxotrophs. In addition to ACC pyruvate carboxylase and an additional biotin-containing protein of unknown function fail to be biotinylated in BPL1-defective yeast mutants. In this study, one of these mutants, bpl1-C25/17, is shown to contain an amber stop codon at position 151 of the 689-amino-acid BPL sequence. In bpl1-C25/17 cells, de novo fatty acid synthesis is almost absent (< 2% of the wild type), while very-long-chain fatty acid (VLCFA) synthesis and, to some extent, medium-long-chain fatty acid elongation are still active. Hence, endogenous malonyl-CoA synthesis is reduced but not abolished by the translational stop mutation. A low rate of intact-BPL synthesis is accomplished in the mutant by occasional readthrough of the bpl1-C25/17 UAG nonsense triplet by normal yeast tRNA(Gln)(CAG). Correspondingly, ACC biotinylation is severely reduced though not completely absent in the two bpl1 mutants studied in this work. Residual BPL1 expression in bpl1-C25/17 cells is increased to a level allowing wild-type-like growth by transformation with high copy numbers of either the wild-type tRNA(Gln)(CAG) or the mutant bpl1-C25/17 genes. It is concluded that the lethality of BPL1 deletants is due to the lack of malonyl-CoA-dependent VLCFA synthesis and that the viability of distinct ACC-defective point mutants is due to their maintenance of a critical level of malonyl-CoA and, hence, VLCFA production. The residual capacity of malonyl-CoA synthesis, though, is inadequate to allow cytoplasmic bulk de novo fatty acid synthesis, nor does it support mutant growth on 13:0 as the only dietary fatty acid. ACC-defective mutants are respiratory deficient, which is attributed to the failure of mitochondrial fatty acid synthesis. Since lipoic acid levels of ACC1 and BPL1 mutants are essentially normal, an unknown product of mitochondrial fatty acid synthesis appears to be critically reduced in malonyl-CoA-deficient yeast cells.

Mitochondrial fatty acid synthesis: a relic of endosymbiontic origin and a specialized means for respiration

Genes that encode mitochondrial homologues to the bacterial enzymes of fatty acid synthesis were found in various eukaryotic species. Inactivation of these genes leads to a disturbed mitochondrial respiration and an increase in mitochondrial lysophospholipids. We postulate that there is a mitochondrial biosynthetic system providing fatty acids for phospholipid repair. The mitochondrial acyl carrier protein may also play another role, supporting the formation of the respiratory NADH:ubiquinone oxidoreductase.

Dietary medium-chain triglycerides can prevent changes in myosin and SR due to CPT-1 inhibition by etomoxir

To define determinants of subcellular structures of heart, Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) were treated for 5 wk with 15 mg.kg-1.day-1 etomoxir [reduces mitochondrial carnitine palmitoyltransferase-1 (CPT-1) activity and fatty acid synthesis]. To bypass CPT-1 inhibition, etomoxir-treated rats were fed a medium-chain fatty acid (MCFA) diet. Etomoxir induced a proportionate growth of heart, which could partially (WKY, P < 0.05) or completely (SHR, P < 0.05) be prevented by the MCFA diet. Also the etomoxir-induced increase in myosin V1 was partially prevented (P < 0.05). Etomoxir increased (P < 0.05) rate of sarcoplasmic reticulum (SR) Ca2+ uptake of WKY and SHR ventricular homogenates in the presence or absence of the SR Ca2+ release inhibitor ruthenium red. The MCFA diet resulted in SR Ca2+ uptake rates that were in between those of etomoxir-treated and untreated rats. The in vitro 32P incorporation into phospholamban and troponin I did not differ significantly in WKY. Etomoxir induced, however, an increase (P < 0.05) in the phosphorylated intermediate of the Ca2+ adenosinetriphosphatase in WKY that was prevented by the MCFA diet. In SHR, etomoxir increased the in vitro phospholamban phosphorylation, which was reduced compared with WKY. The data show that myosin and SR are affected by a chronically altered substrate utilization of heart.

CPT-1 inhibition by etomoxir has a chamber-related action on cardiac sarcoplasmic reticulum and isomyosins

To characterize the effect of an altered substrate utilization for cardiac sarcoplasmic reticulum (SR) Ca2+ transport, normotensive rats were treated for 5 wk with 15 mg.kg-1.day-1 enantiomeric etomoxir, which inhibits mitochondrial carnitine palmitoyltransferase-1 (CPT-1) and fatty acid synthesis. Ca2+ uptake rates of left and right ventricular homogenates were differentially (P < 0.05, two-way analysis of variance) increased by 38 and 13%, respectively. Increased (P < 0.05) transport rates were also observed in the presence of ryanodine. The differences were considerably reduced in the protein kinase A-stimulated state. The levels of phosphorylated phospholamban (PLB) and troponin I as well as immunoreactive PLB were not affected. By contrast, phosphoenzyme levels (E-P) of the SR Ca2+ pump were increased in left ventricular (LV) homogenates. Values of LV E-P and Ca2+ uptake were linearly correlated (P < 0.05) with the myosin V1 proportions in control (31.7 +/- 1.8% V1) and treated (58.3 +/- 2.5% V1) rats. Thus in the left ventricle the metabolic influences have a coordinated action on two distinct proteins involved in relaxation or contraction. The chamber-specific differences in SR function suggest a more pronounced effect of etomoxir in functional states characterized by a reduced Ca2+ transport rate and myosin V1 proportion.

Purification and some properties of short chain-length specific trans-2-enoyl-CoA reductase in mitochondria of Euglena gracilis.

Short chain-length specific trans-2-enoyl-CoA reductase (reductase I), which contributed to mitochondrial fatty acid synthesis, was purified about 200-fold from crude extract of mitochondria in Euglena gracilis. It had a molecular weight of 39,000, and consisted of two dissimilar subunits with molecular weights of 15,000 and 25,000. The enzyme utilized crotonyl-CoA as the most active substrate and showed negative cooperativity in the reaction with the substrate. NADH was the sole electron donor. Some divalent cations were inhibitory to the enzyme when incubated with the enzyme prior to the start of the reaction. The reductase apparently contained loosely bound FAD.

The physiological role of oxygen-sensitive pyruvate dehydrogenase in mitochondrial fatty acid synthesis in Euglena gracilis

In Euglena gracilis a malonyl-CoA-independent fatty acid-synthetic system, in which fatty acids are synthesized directly from acetyl-CoA as both primer and C 2 donor, occurs in mitochondria, and the system contributes to the wax ester fermentation. The activity of fatty acid synthesis in the mitochondrial system was enhanced about six times when an artificial acetyl-CoA-regenerating system was present, indicating that the fatty acid-synthetic activity is controlled by the ratio of acetyl-CoA against CoA. When fatty acids were synthesized using pyruvate instead of acetyl-CoA as substrate, a high activity, about 30 times higher than that from acetyl-CoA, was found under anaerobic conditions (below 10 −5, m oxygen), while in aerobiosis fatty acids were not synthesized at all. CoA, NADH, and NADP + were required as cofactors for fatty acid synthesis from pyruvate. It was indicated that high activity of fatty acid synthesis from pyruvate due to the high ratio of acetyl-CoA against CoA was maintained by the action of the oxygen-sensitive pyruvate dehydrogenase found in Euglena mitochondria. When [2- 14C]pyruvate was fed into intact mitochondria under anaerobic conditions, radioactive fatty acids were formed in the presence of malate, which provided reducing power for the matrix.

Primary role of decreased fatty acid synthesis in insulin resistance of large rat adipocytes.

The ability of large fat cells from spontaneously obese rats to synthesize fatty acids from D-[1-14C]glucose, D-[6-14C]glucose, or [2-14C]pyruvate was markedly diminished compared to small fat cells from lean animals. Furthermore, fatty acid synthetase and acetyl coenzyme A carboxylase activities in dialyzed homogenates of large fat cells were inhibited by 84 and 90%, respectively, compared to small cells. Pentose shunt activity, but not glycolytic flux, was also markedly inhibited in large fat cells incubated with or without insulin. However, the NADPH oxidant vitamin K5 completely restored pentose shunt activity in large cells to the elevated levels observed in small fat cells in the presence of this agent or insulin. Furthermore, inhibition of mitochondrial oxidation and fatty acid synthesis in small cells by rotenone led to a secondary inhibition of pentose shunt activity indicating a link between these two pathways. Direct measurements of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities in fat cell homogenates showed no difference between cell types. The data provide strong support for the hypothesis that the fatty acid synthetic pathway is the primary metabolic defect in large insulin-resistant rat adipocytes, a defect which secondarily leads to inhibited pentose shunt activity.

Effect of cholesterol feeding and estrogen treatment on synthesis of fatty acids in liver

The effect of cholesterol feeding and estrogen administration on synthesis of fatty acids in liver mitochondria, microsomes and cytoplasm of male rabbits has been investigated. The synthesis was measured by the incorporation of [1- 14C]acetyl CoA or [2- 14C]malonyl CoA into long chain fatty acids under optimal conditions. It was found that atherogenesis markedly decreased the fatty acid synthesis in cytoplasm. The mitochondrial fatty acid synthesis was not affected by the disease. There was a small but measurable decrease in the synthesis of fatty acids in microsomes. Estrogen had no effect on the synthesis of fatty acids in mitochondria or microsomes. But if effectively counteracted, after a short lag period, the decreased synthesis of cytoplasmic fatty acids observed in atherosclerosis. It is possible that liver fatty acid synthetase is one of the enzyme systems through which estrogens exert their atherosclerosis-retarding effect. The decreased cytoplasmic fatty acid synthesis observed in atherosclerosis might account for the low levels of saturated fatty acids reported in liver and plasma lipids of atherosclerotic animals.