acyl-CoA Thioesterase Research Articles

Methionine-Derived Metabolites in Apoptosis: Therapeutic Opportunities for Inhibitors of their Metabolism in Chemoresistant Cancer Cells

Methionine, in addition to its role in protein synthesis, participates in 3 important cellular functions: as AdoMet in transmethylation; as decarboxylated-AdoMet in aminopropylation; as homocysteine its demethylated form, in trans-sulphuration. Here we provide evidence from the literature and from our own work for a fourth role for its oxoacid: 4-methylthio-2-oxo-butanoate (MTOB) in apoptosis [28,29]. MTOB enters 2 pathways: (a) transamination by glutamine-transaminase K to methionine[13,14].(b)oxidative decarboxylation by the mitochondrial Branched-Chain-Oxo-Acid-Dehydrogenase-Complex to methional and finally to methylthiopropanoyl CoA (MTPCoA) [26,27]. Some of the methional formed after MTOB decarboxylation leaks into the cytoplasm as free methional [29]. Exogenous methional induces apoptosis in normal and cancer cells in culture [28, 29] but not in those overexpressing the antiapoptotic gene bcl2 [30]. In physiologically-induced apoptosis e.g; trophic factor (IL3) withdrawal, methional leakage is decreased [29] suggesting that MTPCoA is also involved in apoptosis. Both methional and MTPCoA give rise to metabolites that may act as cross-linking agents. In the case of methional, the CH3-S moiety is lost and malondialdehyde (MDA) is formed when methional is subjected to ( )OH attack [29]. MDA generated in situ from 1,3-propanediol, induces DNA-protein cross-linking [41].With regard to MTPCoA, it is metabolized to malonic semialdehyde CoA (MASACoA) with loss of the CH3-S moiety [48,49]. The capacity of MASACoA to form cross-links has not yet been established experimentally, but it could be a substrate for one of the histone acyl transferases [50, 51] and so form amides via the CoA at one end and imines by its CHO group at the other, with amino groups on proteins. Chromatin cross-linking/condensation is one of the hall-marks of apoptosis [40]. Methional, MDA and other apoptogenic aldehydes like 4-hydroxy-2-nonenal are oxidized by ALDHs to non-apoptogenic carboxylic acids [29,44, 45,68] but retain their apoptotic activity when the ALDHs are inhibited [98,110]. MASACoA would also lose its cross-linking capacity if its CoA moiety were putatively hydrolysed by ALDHs and/or acylCoA thioesterases [56,58,88,89]. ALDH inhibitors that control cellular MDA and possibly MASACoA homeostasis are cited as examples of targeted therapeutic approaches in chemoresistant cancers [62,84,97,98,110].

Thioesterase superfamily member 2 (Them2)/acyl-CoA thioesterase 13 (Acot13): a homotetrameric hotdog fold thioesterase with selectivity for long-chain fatty acyl-CoAs

Them2 (thioesterase superfamily member 2) is a 140-amino-acid protein of unknown biological function that comprises a single hotdog fold thioesterase domain. On the basis of its putative association with mitochondria, accentuated expression in oxidative tissues and interaction with StarD2 (also known as phosphatidylcholine-transfer protein, PC-TP), a regulator of fatty acid metabolism, we explored whether Them2 functions as a physiologically relevant fatty acyl-CoA thioesterase. In solution, Them2 formed a stable homotetramer, which denatured in a single transition at 59.3 degrees C. Them2 exhibited thioesterase activity for medium- and long-chain acyl-CoAs, with Km values that decreased exponentially as a function of increasing acyl chain length. Steady-state kinetic parameters for Them2 were characteristic of long-chain mammalian acyl-CoA thioesterases, with minimal values of Km and maximal values of kcat/Km observed for myristoyl-CoA and palmitoyl-CoA. For these acyl-CoAs, substrate inhibition was observed when concentrations approached their critical micellar concentrations. The acyl-CoA thioesterase activity of Them2 was optimized at physiological temperature, ionic strength and pH. For both myristoyl-CoA and palmitoyl-CoA, the addition of StarD2 increased the kcat of Them2. Enzymatic activity was decreased by the addition of phosphatidic acid/phosphatidylcholine small unilamellar vesicles. Them2 expression, which was most pronounced in mouse heart, was associated with mitochondria and was induced by activation of PPARalpha (peroxisome-proliferator-activated receptor alpha). We conclude that, under biological conditions, Them2 probably functions as a homotetrameric long-chain acyl-CoA thioesterase. Accordingly, Them2 has been designated as the 13th member of the mammalian acyl-CoA thioesterase family, Acot13.

Crystal structure of human mitochondrial acyl-CoA thioesterase (ACOT2)

Acyl-CoA thioesterases (ACOTs) catalyze the hydrolysis of CoA esters to free CoA and carboxylic acids and have important functions in lipid metabolism and other cellular processes. Type I ACOTs are found only in animals and contain an α/β hydrolase domain, through currently no structural information is available on any of these enzymes. We report here the crystal structure at 2.1 Å resolution of human mitochondrial ACOT2, a type I enzyme. The structure contains two domains, N and C domains. The C domain has the α/β hydrolase fold, with the catalytic triad Ser294–His422–Asp388. The N domain contains a seven-stranded β-sandwich, which has some distant structural homologs in other proteins. The active site is located in a large pocket at the interface between the two domains. The structural information has significant relevance for other type I ACOTs and related enzymes.

The Akt C-terminal modulator protein is an acyl-CoA thioesterase of the Hotdog-Fold family.

Herein, we report on an in vitro kinetic activity analysis that demonstrates that the protein known as the Akt C-terminal modulator protein is a broad-range, high-activity acyl-CoA thioesterase. In vitro tests of possible activity regulation by product inhibition or by Akt1 binding gave negative results. Truncation mutants confined the thioesterase activity to the C-terminal domain, consistent with our threading model. The N-terminal domain of unknown fold and function was found to contribute to solubility.

S1787 Regulation of Acyl-CoA Thioesterase Activity By Steroidogenic Acute Regulatory Transfer-Related (START) Domains: In Vitro Evidence for Reversible Control in the Liver

S1787 Regulation of Acyl-CoA Thioesterase Activity By Steroidogenic Acute Regulatory Transfer-Related (START) Domains: In Vitro Evidence for Reversible Control in the Liver

The nuclear receptor CAR (NR1I3) regulates serum triglyceride levels under conditions of metabolic stress

The nuclear receptor constitutive androstane receptor (CAR) (NR1I3) regulates hepatic genes involved in xenobiotic detoxification as well as genes involved in energy homeostasis. We provide data that extend the role of CAR to regulation of serum triglyceride levels under conditions of metabolic/nutritional stress. The typically high serum triglyceride levels of ob/ob mice were completely normalized when crossed onto a Car(-/-) (mice deficient for the Car gene) genetic background. Moreover, increases in serum triglycerides observed after a high-fat diet (HFD) regime were not observed in Car(-/-) animals. Conversely, pharmacological induction of CAR activity using the selective mouse CAR agonist TCPOBOP during HFD feeding resulted in a CAR-dependent increase in serum triglyceride levels. A major regulator of hepatic fatty oxidation is the nuclear receptor PPARalpha (NR1C1). The expression of peroxisome proliferator-activated receptor alpha (PPARalpha) target genes was inversely related to the activity of CAR. Consistent with these observations, Car(-/-) animals exhibited increased hepatic fatty acid oxidation. Treatment of mice with 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) significantly decreased expression of PPARalpha mRNA as well as Cyp4a14, CPT1alpha, and cytosolic Acyl-CoA thioesterase (CTE) in the liver. These data have implications in disease therapy such as for diabetes and nonalcoholic steatohepatitis (NASH).

Crystallography and protein–protein interactions: biological interfaces and crystal contacts

Crystallography is commonly used for studying the structures of protein-protein complexes. However, a crystal structure does not define a unique protein-protein interface, and distinguishing a 'biological interface' from 'crystal contacts' is often not straightforward. A number of computational approaches exist for distinguishing them, but their error rate is high, emphasizing the need to obtain further data on the biological interface using complementary structural and functional approaches. In addition to reviewing the computational and experimental approaches for addressing this problem, we highlight two relevant examples. The first example from our laboratory involves the structure of acyl-CoA thioesterase 7, where each domain of this two-domain protein was crystallized separately, but both yielded a non-functional assembly. The structure of the full-length protein was uncovered using a combination of complementary approaches including chemical cross-linking, analytical ultracentrifugation and mutagenesis. The second example involves the platelet glycoprotein Ibalpha-thrombin complex. Two groups reported the crystal structures of this complex, but all the interacting interfaces differed between the two structures. Our computational analysis did not fully resolve the reasons for the discrepancies, but provided interesting insights into the system. This review highlights the need to complement crystallographic studies with complementary experimental and computational approaches.

Skeletal Muscle Group VIA Phospholipase A2 (iPLA2β): Expression and Role in Fatty Acid Oxidation

Among the phospholipases A 2 (PLA 2s) are the group VI Ca (2+)-independent PLA 2s (iPLA 2s), and expression of multiple transcripts of iPLA 2 in skeletal muscle has been reported. In the present study, phospholipase activity and sequential ATP and calmodulin affinity column chromatography analyses reveal that skeletal muscle iPLA 2 exhibits properties characteristic of the iPLA 2beta isoform. The phospholipase activity of iPLA 2beta has been demonstrated to participate in signal transduction, cell proliferation, and apoptosis. We report here that skeletal muscle from iPLA 2beta-null mice, relative to wild-type muscle, exhibits a reduced capacity to oxidize palmitate but not palmitoyl-CoA or acetyl-CoA in the absence of changes in fatty acid transporters CD36 and CPT1 or beta-hydroxyacyl-CoA dehydrogenase activity. Recently, purified iPLA 2beta was demonstrated to manifest a thioesterase activity which catalyzes hydrolysis of fatty acyl-CoAs. The liberated CoA-SH facilitates fatty acid transport into the mitochondria. In this regard, we find that fractions eluted from the ATP column and containing iPLA 2beta phospholipase activity also contained acyl-CoA thioesterase activity that was inhibited by the bromoenol lactone (BEL) suicide inhibitor of iPLA 2beta. We further find that acyl-CoA thioesterase activity in skeletal muscle preparations from iPLA 2beta-null mice is significantly reduced, relative to WT activity. These findings suggest that the absence of acyl-CoA thioesterase activity of iPLA 2beta can lead to reduced fatty acyl-CoA generation and impair fatty acid oxidation in iPLA 2beta-null mice. Our findings therefore reveal a novel function of iPLA 2beta, related not to its phospholipase activity but to its thioesterase activity, which contributes to optimal fatty acid oxidation in skeletal muscle.

Structural studies of acyl-CoA thioesterase 7 and its role in inflammation

Structural studies of acyl-CoA thioesterase 7 and its role in inflammation

A Novel Paradigm of Fatty Acid β-Oxidation Exemplified by the Thioesterase-Dependent Partial Degradation of Conjugated Linoleic Acid That Fully Supports Growth of Escherichia coli

An alternative pathway of beta-oxidation for unsaturated fatty acids was studied in Escherichia coli. 9- cis,11- trans-Octadecadienoic acid (conjugated linoleic acid), a potential substrate of this pathway, was shown to support growth of E. coli in the absence of any other carbon source. The identification of 3,5-dodecadienoic acid in the growth medium revealed the partial beta-oxidation of conjugated linoleic acid to 3,5-dodecadienoyl-CoA, which was hydrolyzed to 3,5-dodecadienoic acid and released from cells. The involvement of acyl-CoA thioesterases in this process was evaluated by determining the substrate specificity of thioesterase II and comparing it with that of a novel thioesterase (thioesterase III) and by assessing mutant strains devoid of one or both of these thioesterases for growth on conjugated linoleic acid. Both thioesterases were highly active with 3,5-dodecadienoyl-CoA as substrate. A deficiency of either thioesterase decreased the growth rate of cells on conjugated linoleic acid but not on palmitic acid. The absence of both thioesterases reduced the cellular growth in a cumulative manner but did not abolish it. It is concluded that thioesterases II and III and at least one other thioesterase function in the partial degradation of conjugated linoleic acid via the thioesterase-dependent pathway of beta-oxidation, which provides all energy and carbon precursors required for the growth of E. coli.

Identification and Characterization of Escherichia coli Thioesterase III That Functions in Fatty Acid β-Oxidation

When Escherichia coli is grown on oleic acid as the sole carbon source, most of this fatty acid is completely degraded by beta-oxidation. However, approximately 10% of the oleic acid is only partially degraded to 3,5- cis-tetradecadienoyl-CoA, which is hydrolyzed to 3,5- cis-tetradecadienoic acid and released into the growth medium. An investigation of thioesterases involved in this novel pathway of beta-oxidation led to the identification of a new thioesterase (thioesterase III) that is induced by growth of E. coli on oleic acid. This enzyme was partially purified and identified as the ybaW gene product by mass spectrometric analysis of tryptic peptides. The ybaW gene, which has a putative consensus sequence for binding the fatty acid degradation repressor, was cloned and expressed in E. coli. Thioesterase III was shown to be a long-chain acyl-CoA thioesterase that is most active with 3,5-tetradecadienoyl-CoA, a minor metabolite of oleate beta-oxidation. Its substrate specificity and induction by fatty acids agree with its proposed function in the thioesterase-dependent pathway of beta-oxidation. Thioesterase III is proposed to hydrolyze metabolites of beta-oxidation that are resistant to further degradation and that would inhibit the flux through the pathway if they were allowed to accumulate.

Identification of Disulfide-Containing Chemical Cross-Links in Proteins Using MALDI-TOF/TOF-Mass Spectrometry

Cross-linking can be used to identify spatial relationships between amino acids in proteins or protein complexes. A rapid and sensitive method for identifying the site of protein cross-linking using dithiobis(sulfosuccinimidyl propionate) (DTSSP) is presented and illustrated with experiments using murine cortactin, actin and acyl-CoA thioesterase. A characteristic 66 Da doublet, which arises from the asymmetric fragmentation of the disulfide of DTSSP-modified peptides, is observed in the mass spectra obtained under MALDI-TOF/TOF-MS conditions and allows rapid assignment of cross-links in modified proteins. This doublet is observed not only for linear cross-linked peptides but also in the mass spectra of cyclic cross-linked peptides when simultaneous fragmentation of the disulfide and the peptide backbone occurs. We suggest a likely mechanism for this fragmentation. We use guanidinylation of the cross-linked peptides with O-methyl isourea to extend the coverage of cross-linked peptides observed in this MALDI-MS technique. The methodology we report is robust and amenable to automation, and permits the analysis of native cystines along with those introduced by disulfide-containing cross-linkers.

New Enzymes Involved in the Mechanism of Action of Epidermal Growth Factor in a Clonal Strain of Leydig Tumor Cells

The studies presented herein were designed to investigate the effect of mouse epidermal growth factor (mEGF) on arachidonic acid (AA) release in a clonal strain of cultured murine Leydig cells (designed MA-10). In MA-10 cells, mEGF promotes AA release and metabolism to lipoxygenated products to induce the steroidogenic acute regulatory (StAR) protein. However, the mechanism by which mEGF releases AA in these cells is not totally elucidated. We show that mEGF produces an increment in the mitochondrial AA content in a short-term incubation (30 min). This AA is released by the action of a mitochondrial acyl-CoA thioesterase (Acot2), as demonstrated in experiments in which Acot2 was down or overexpressed. This AA in turn regulates the StAR protein expression, indirect evidence of its metabolism to lipoxygenated products. We also show that mEGF induces the expression (mRNA and protein) of Acot2 and an acyl-CoA synthetase that provides the substrate, arachidonyl-CoA, to Acot2. This effect is also observed in another steroidogenic cell line, the adrenocortical Y1 cells. Taken together, our results show that: 1) mEGF can induce the generation of AA in a specific compartment of the cells, i.e. the mitochondria; 2) mEGF can up-regulate acyl-CoA synthetase and Acot2 mRNA and protein levels; and 3) mEGF-stimulated intramitochondrial AA release leads to StAR protein induction.

Structural and enzymatic characterization of HP0496, a YbgC thioesterase from Helicobacter pylori

YbgC proteins are bacterial acyl-CoA thioesterases associated with the Tol-Pal system. This system is important for cell envelope integrity and is part of the cell division machinery. In E. coli, YbgC associates with the cell membrane and is part of a protein network involved in lipid biogenesis. In the human pathogen Helicobacter pylori, a putative homologue of YbgC, named HP0496, was found to interact with the cytotoxin CagA by two different studies. We have determined its crystal structure and characterized its enzymatic activity. The structure of HP0496 shows that it is a member of the hot-dog family of proteins, with a epsilongamma tetrameric arrangement. Finally, enzymatic assays performed with the purified protein showed that HP0496 is an acyl-CoA thioesterase that favors long-chain substrates.

Short- and medium-chain carnitine acyltransferases and acyl-CoA thioesterases in mouse provide complementary systems for transport of beta-oxidation products out of peroxisomes.

Peroxisomes metabolize a variety of lipids, acting as a chain-shortening system that produces acyl-CoAs of varying chain lengths, including acetyl-CoA and propionyl-CoA. It is, however, still largely unknown how beta-oxidation products exit peroxisomes and where they are further metabolized. Peroxisomes contain carnitine acetyltransferase (CRAT) and carnitine octanoyltransferase (CROT) that produce carnitine esters for transport out of peroxisomes, together with recently characterized acyl-CoA thioesterases (ACOTs) that produce free fatty acids. Here we have performed tissue expression profiling of the short- and medium-chain carnitine acyltransferases Crat, Crot and the short- and medium-chain thioesterases (Acot12) and (Acot5), and show that they are largely expressed in different tissues, suggesting that they do not compete for the same substrates but rather provide complementary systems for transport of metabolites across the peroxisomal membrane. These data also explain earlier observed tissue differences in peroxisomal production of acetyl-CoA/acetyl-carnitine/acetate and underscores the differences in peroxisome function in various organs.

Structure of YciA from Haemophilus influenzae (HI0827), a Hexameric Broad Specificity Acyl-Coenzyme A Thioesterase,

The crystal structure of HI0827 from Haemophilus influenzae Rd KW20, initially annotated "hypothetical protein" in sequence databases, exhibits an acyl-coenzyme A (acyl-CoA) thioesterase "hot dog" fold with a trimer of dimers oligomeric association, a novel assembly for this enzyme family. In studies described in the preceding paper [Zhuang, Z., Song, F., Zhao, H., Li, L., Cao, J., Eisenstein, E., Herzberg, O., and Dunaway-Mariano, D. (2008) Biochemistry 47, 2789-2796], HI0827 is shown to be an acyl-CoA thioesterase that acts on a wide range of acyl-CoA compounds. Two substrate binding sites are located across the dimer interface. The binding sites are occupied by two CoA molecules, one with full occupancy and the second only partially occupied. The CoA molecules, acquired from HI0827-expressing Escherichia coli cells, remained tightly bound to the enzyme through the protein purification steps. The difference in CoA occupancies indicates a different substrate affinity for each of the binding sites, which in turn implies that the enzyme might be subject to allosteric regulation. Mutagenesis studies have shown that the replacement of the putative catalytic carboxylate Asp44 with an alanine residue abolishes activity. The impact of this mutation is seen in the crystal structure of D44A HI0827. Whereas the overall fold and assembly of the mutant protein are the same as those of the wild-type enzyme, the CoA ligands are absent. The dimer interface is perturbed, and the channel that accommodates the thioester acyl chain is more open and wider than that observed in the wild-type enzyme. A model of intact substrate bound to wild-type HI0827 provides a structural rationale for the broad substrate range.

Altered expression patterns of lipid metabolism genes in an animal model of HCV core-related, nonobese, modest hepatic steatosis

BackgroundBecause the gene expression patterns of nonobese hepatic steatosis in affected patients remain unclear, we sought to explore these patterns using an animal model of nonobese hepatic steatosis.MethodsWe developed mice that conditionally express the hepatitis C virus (HCV) core protein regulated by the tetracycline transactivator (tTA). Microarray analyses and reverse-transcription polymerase chain reaction were performed using liver samples of both the double transgenic mice (DTM), which express both the HCV core and tTA, and single transgenic mice (STM), which express tTA alone, at 2 months of age. Functional categories of genes with altered expression were classified using gene ontology programs. Serum glucose, lipid levels, and systemic blood pressure were also measured.ResultsApproximately 20–30% of hepatocytes from the DTM were steatotic. No significant differences were observed in the serum glucose, lipid content, or blood pressure levels between the DTM and STM. Gene expression analyses revealed Sterol-regulatory element-binding protein (SREBP) pathway activation and dysregulation of the following genes involved in lipid metabolism: 3-hydroxy-3-methylglutaryl-coenzyme A synthase 1, Apolipoprotein AII, Apolipoprotein CI, acyl-CoA thioesterase I, and fatty acid binding protein 1; in mitochondrial function: solute carrier family 25 member 25 and cytochrome c oxidase subunit II; in immune reaction: complement component 3, lymphocyte antigen 6 complex, locus A, lymphocyte antigen 6 complex, locus C, lymphocyte antigen 6 complex, locus D, and lymphocyte antigen 6 complex, locus E.ConclusionSome genes of lipid metabolism, mitochondrial function, and immune reaction and the SREBP pathway are involved in HCV core-related, nonobese, modest hepatic steatosis.

Proteomics Characterization of Mouse Kidney Peroxisomes by Tandem Mass Spectrometry and Protein Correlation Profiling

The peroxisome represents a ubiquitous single membrane-bound key organelle that executes various metabolic pathways such as fatty acid degradation by alpha- and beta-oxidation, ether-phospholipid biosynthesis, metabolism of reactive oxygen species, and detoxification of glyoxylate in mammals. To fulfil this vast array of metabolic functions, peroxisomes accommodate approximately 50 different enzymes at least as identified until now. Interest in peroxisomes has been fueled by the discovery of a group of genetic diseases in humans, which are caused by either a defect in peroxisome biogenesis or the deficient activity of a distinct peroxisomal enzyme or transporter. Although this research has greatly improved our understanding of peroxisomes and their role in mammalian metabolism, deeper insight into biochemistry and functions of peroxisomes is required to expand our knowledge of this low abundance but vital organelle. In this work, we used classical subcellular fractionation in combination with MS-based proteomics methodologies to characterize the proteome of mouse kidney peroxisomes. We could identify virtually all known components involved in peroxisomal metabolism and biogenesis. Moreover through protein localization studies by using a quantitative MS screen combined with statistical analyses, we identified 15 new peroxisomal candidates. Of these, we further investigated five candidates by immunocytochemistry, which confirmed their localization in peroxisomes. As a result of this joint effort, we believe to have compiled the so far most comprehensive protein catalogue of mammalian peroxisomes.

Lipid Synthesis in Lactation: Diet and the Fatty Acid Switch

The lipid component of milk provides the critical nutritional source for generating both energy and essential nutrients to the growth of the newborn. Three types of substrate are utilized to synthesize milk triacylglycerides (TAG): dietary fat, fatty acids mobilized from adipose tissue stores, and lipids synthesized de novo synthesis from glucose and other dietary precursors, a process often referred to as de novo lipogenesis. The utilization of these various sources for TAG synthesis by the mammary epithelial cells is influenced by both the stage of lactation and the diet. From studies of gene expression in FVB mice, we observed that genes for beta-oxidation of fatty acids are downregulated along with the expression of Acyl-CoA thioesterase 1 (ACOT1). As a control mechanism we propose that during pregnancy ACOT1 provides a supply of cytoplasmic free fatty acids which increase the activation of PPARgamma. Ligand-induced activation of the PPAR/RXR transcription factor complex by free fatty acids, upregulates expression of genes required for beta-oxidation of fatty acids. The fall in ACOTs at secretory activation may facilitate the switch to lipogenesis perhaps mediated by activation of the LXR/RXR transcription factor complex. The response to changes in the supply of dietary lipids, on the other hand, is likely to be mediated by SREBP1, possibly acting through modulation of Spot 14. Stability of SREBP1 may be enhanced by a significant increase in Akt at secretory activation. These regulatory pathways may be critical to the production of milk with a balanced TAG composition to support neonatal development of the newborn.

Peroxisomes, Refsum's disease and the α- and ω-oxidation of phytanic acid

In the present paper, we describe the current state of knowledge regarding the enzymology of the phytanic acid alpha-oxidation pathway. The product of phytanic acid alpha-oxidation, i.e. pristanic acid, undergoes three cycles of beta-oxidation in peroxisomes after which the products, including 4,8-dimethylnonanoyl-CoA, propionyl-CoA and acetyl-CoA, are exported from the peroxisome via one of two routes, including (i) the carnitine-dependent route, mediated by CRAT (carnitine acetyltransferase) and CROT (carnitine O-octanoyltransferase), and (ii) the free acid route, mediated by one or more of the peroxisomal ACOTs (acyl-CoA thioesterases). We also describe our recent data on the omega-oxidation of phytanic acid, especially since pharmacological up-regulation of this pathway may form the basis of a new treatment strategy for ARD (adult Refsum's disease). In patients suffering from ARD, phytanic acid accumulates in tissues and body fluids due to a defect in the alpha-oxidation system.