A fast and versatile method for extraction and quantitation of long-chain acyl-CoA esters from tissue: content of individual long-chain acyl-CoA esters in various tissues from fed rat

Auto-fatty acylation of transcription factor RFX3 regulates ciliogenesis

Defects in cilia have been associated with an expanding human disease spectrum known as ciliopathies. Regulatory Factor X 3 (RFX3) is one of the major transcription factors required for ciliogenesis and cilia functions. In addition, RFX3 regulates pancreatic islet cell differentiation and mature β-cell functions. However, how RFX3 protein is regulated at the posttranslational level remains poorly understood. Using chemical reporters of protein fatty acylation and mass spectrometry analysis, here we show that RFX3 transcriptional activity is regulated by S-fatty acylation at a highly conserved cysteine residue in the dimerization domain. Surprisingly, RFX3 undergoes enzyme-independent, "self-catalyzed" auto-fatty acylation and displays preferences for 18-carbon stearic acid and oleic acid. The fatty acylation-deficient mutant of RFX3 shows decreased homodimerization; fails to promote ciliary gene expression, ciliogenesis, and elongation; and impairs Hedgehog signaling. Our findings reveal a regulation of RFX3 transcription factor and link fatty acid metabolism and protein lipidation to the regulation of ciliogenesis.

Skeletal muscle phosphatidylcholine and phosphatidylethanolamine are related to insulin sensitivity and respond to acute exercise in humans

Several recent reports indicate that the balance of skeletal muscle phosphatidylcholine (PC) and phosphatidylethanolamine (PE) is a key determinant of muscle contractile function and metabolism. The purpose of this study was to determine relationships between skeletal muscle PC, PE and insulin sensitivity, and whether PC and PE are dynamically regulated in response to acute exercise in humans. Insulin sensitivity was measured via intravenous glucose tolerance in sedentary obese adults (OB; n = 14), individuals with type 2 diabetes (T2D; n = 15), and endurance-trained athletes (ATH; n = 15). Vastus lateralis muscle biopsies were obtained at rest, immediately after 90 min of cycle ergometry at 50% maximal oxygen consumption (V̇o2 max), and 2-h postexercise (recovery). Skeletal muscle PC and PE were measured via infusion-based mass spectrometry/mass spectrometry analysis. ATH had greater levels of muscle PC and PE compared with OB and T2D (P < 0.05), with total PC and PE positively relating to insulin sensitivity (both P < 0.05). Skeletal muscle PC:PE ratio was elevated in T2D compared with OB and ATH (P < 0.05), tended to be elevated in OB vs. ATH (P = 0.07), and was inversely related to insulin sensitivity among the entire cohort (r = -0.43, P = 0.01). Muscle PC and PE were altered by exercise, particularly after 2 h of recovery, in a highly group-specific manner. However, muscle PC:PE ratio remained unchanged in all groups. In summary, total muscle PC and PE are positively related to insulin sensitivity while PC:PE ratio is inversely related to insulin sensitivity in humans. A single session of exercise significantly alters skeletal muscle PC and PE levels, but not PC:PE ratio.

Two Predicted Transmembrane Domains Exclude Very Long Chain Fatty acyl-CoAs from the Active Site of Mouse Wax Synthase

Wax esters are used as coatings or storage lipids in all kingdoms of life. They are synthesized from a fatty alcohol and an acyl-CoA by wax synthases. In order to get insights into the structure-function relationships of a wax synthase from Mus musculus, a domain swap experiment between the mouse acyl-CoA:wax alcohol acyltransferase (AWAT2) and the homologous mouse acyl-CoA:diacylglycerol O-acyltransferase 2 (DGAT2) was performed. This showed that the substrate specificity of AWAT2 is partially determined by two predicted transmembrane domains near the amino terminus of AWAT2. Upon exchange of the two domains for the respective part of DGAT2, the resulting chimeric enzyme was capable of incorporating up to 20% of very long acyl chains in the wax esters upon expression in S. cerevisiae strain H1246. The amount of very long acyl chains in wax esters synthesized by wild type AWAT2 was negligible. The effect was narrowed down to a single amino acid position within one of the predicted membrane domains, the AWAT2 N36R variant. Taken together, we provide first evidence that two predicted transmembrane domains in AWAT2 are involved in determining its acyl chain length specificity.

Methylcitrate cycle defines the bactericidal essentiality of isocitrate lyase for survival of Mycobacterium tuberculosis on fatty acids

Few mutations attenuate Mycobacterium tuberculosis (Mtb) more profoundly than deletion of its isocitrate lyases (ICLs). However, the basis for this attenuation remains incompletely defined. Mtb's ICLs are catalytically bifunctional isocitrate and methylisocitrate lyases required for growth on even and odd chain fatty acids. Here, we report that Mtb's ICLs are essential for survival on both acetate and propionate because of its methylisocitrate lyase (MCL) activity. Lack of MCL activity converts Mtb's methylcitrate cycle into a "dead end" pathway that sequesters tricarboxylic acid (TCA) cycle intermediates into methylcitrate cycle intermediates, depletes gluconeogenic precursors, and results in defects of membrane potential and intrabacterial pH. Activation of an alternative vitamin B12-dependent pathway of propionate metabolism led to selective corrections of TCA cycle activity, membrane potential, and intrabacterial pH that specifically restored survival, but not growth, of ICL-deficient Mtb metabolizing acetate or propionate. These results thus resolve the biochemical basis of essentiality for Mtb's ICLs and survival on fatty acids.

Measuring long-chain acyl-coenzyme A concentrations and enrichment using liquid chromatography/tandem mass spectrometry with selected reaction monitoring

Long-chain acyl-coenzymes A (acyl-CoAs) (LCACoA) are the activated forms of long-chain fatty acids and serve as key lipid metabolites. Excess accumulation of intracellular LCACoA, diacylglycerols (DAGs) and ceramides may create insulin resistance with respect to glucose metabolism. We present a new method to measure LCACoA concentrations and isotopic enrichment of palmitoyl-CoA ([U-(13) C]16-CoA) and oleoyl-CoA ([U-(13) C]18:1-CoA) using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) to quantitate seven different LCACoA (C14-CoA, C16-CoA, C16:1-CoA, C18-CoA, C18:1-CoA, C18:2-CoA, C20-CoA). The molecules are separated on a reversed-phase UPLC column using a binary gradient with ammonium hydroxide (NH(4) OH) in water and NH(4) OH in acetonitrile (ACN). The LCACoA are quantified using selected reaction monitoring (SRM) on a triple quadrupole mass spectrometer in positive electrospray ionization (ESI) mode. All LCACoA ions except enriched palmitate enrichment of palmitoyl-CoA ([U(-13)C]16-CoA) and oleoyl-CoA ([U(-13)C]18:1-CoA) using ultra-performance liquid chromatography/mass spectrometry (UPLC/MS/MS) to quantitate seven different LCACoA (C14-CoA, C16-CoA, C16:1-CoA, C18-CoA, C18:1-CoA, C18:2-CoA, C20-CoA). The molecules are separated on a reversed-phase UPLC column using a binary gradient with ammonium hydroxide (NH(4) OH) in water and NH(4) OH in acetonitrile. The LCACoA are quantified using selected reaction monitoring (SRM) on a triple quadrupolemass spectrometer in positive electrospray ionization (ESI) mode. All LCACoA ions except enriched palmitate and oleate were monitored as [M+2+H](+) and [U(13)C]16-CoA and [U(13)C]18:1-CoA were monitored as [M+16+H](+) and [M+18+H](+), respectively. The method is simple, sensitive and efficient (run time as short as 5 min) and allowed us to measure the concentration and detect enrichment in intramyocellular [U(13) C]16-CoA and [U(13) C]18:1-CoA during a low dose intravenous infusion of [U(13) C]palmitate and [U(13) C]oleate in adults undergoing either a saline control experiment or an insulin/glucose infusion experiment. This technique should allow investigators to measure the trafficking of extracellular fatty acids to the intracellular LCACoA pool.

Fenofibrate administration does not affect muscle triglyceride concentration or insulin sensitivity in humans

Animal data suggest that males, in particular, rely on peroxisome proliferator activated receptor-α activity to maintain normal muscle triglyceride metabolism. We sought to examine whether this was also true in men vs women and its relationship to insulin sensitivity (Si). Normolipidemic obese men (n = 9) and women (n = 9) underwent an assessment of Si (intravenous glucose tolerance test) and intramuscular triglyceride (IMTG) metabolism (gas chromatography/mass spectrometry and gas chromatography-combustion isotope ratio mass spectrometry from plasma and muscle biopsies taken after infusion of [U-(13)C]palmitate) before and after 12 weeks of fenofibrate treatment. Women were more insulin sensitive (Si: 5.2 ± 0.7 vs 2.4 ± 0.4 ×10(-4)/ μU/mL, W vs M, P < .01) at baseline despite similar IMTG concentration (41.9 ± 15.5 vs 30.8 ± 5.1 μg/mg dry weight, W vs M, P = .43) and IMTG fractional synthesis rate (FSR) (0.27%/h ± 0.07%/h vs 0.35%/h ± 0.06%/h, W vs M, P = .41) as men. Fenofibrate enhanced FSR in men (0.35 ± 0.06 to 0.54 ± 0.06, P = .05), with no such change seen in women (0.27 ± 0.07 to 0.32 ± 0.13, P = .73) and no change in IMTG concentration in either group (23.0 ± 3.9 in M, P = .26 vs baseline; 36.3 ± 12.0 in W, P = .79 vs baseline). Insulin sensitivity was unaffected by fenofibrate (P ≥ .68). Lower percentage saturation of IMTG in women vs men before (29.1% ± 2.3% vs 35.2% ± 1.7%, P = .06) and after (27.3% ± 2.8% vs 35.1% ± 1.9%, P = .04) fenofibrate most closely related to their greater Si (R(2) = 0.34, P = .10) and was largely unchanged by the drug. Peroxisome proliferator activated receptor-α agonist therapy had little effect on IMTG metabolism in men or women. Intramuscular triglyceride saturation, rather than IMTG concentration or FSR, most closely (but not significantly) related to Si and was unchanged by fenofibrate administration.

Analysis of mammalian fatty acyl-coenzyme A species by mass spectrometry and tandem mass spectrometry

Acyl-CoAs are intermediates of numerous metabolic processes in eukaryotic cells, including beta-oxidation within mitochondria and peroxisomes, and the biosynthesis/remodeling of lipids (e.g. mono-, di-, and triglycerides, phospholipids and sphingolipids). Investigations of lipid metabolism have been advanced by the ability to quantitate acyl-CoA intermediates via liquid chromatography coupled to electrospray ionization-tandem mass spectrometric detection (LC-ESI-MS/MS), which is presently one of the most sensitive and specific analytical methods for both lipids and acyl-CoAs. This review of acyl-CoA analysis by mass spectrometry focuses on mammalian samples and long-chain analytes (i.e. palmitoyl-CoA), particularly reports of streamlined methodology, improved recovery, or expansion of the number of acyl chain-lengths amenable to quantitation.

Rosiglitazone promotes fatty acyl CoA accumulation and excessive glycogen storage in livers of mice without adiponectin

BACKGROUND & AIMS

The beneficial effects of rosiglitazone on non-alcoholic fatty liver disease (NAFLD) have been reported. Rosiglitazone treatment stimulates the production of adiponectin, an insulin-sensitizing adipokine with hepatoprotective functions. The present study aims to investigate the hepatic actions of rosiglitazone in mice without adiponectin.

METHODS

NAFLD was induced in wild type and adiponectin knockout (AKO) mice by high-fat diet feeding. After rosiglitazone treatment, mice were subjected to evaluations on systemic insulin sensitivity, lipid profiles, hepatic steatosis, and inflammation, as well as the expression and activity of key molecules involved in energy metabolism and mitochondrial functions.

RESULTS

Rosiglitazone treatment prevented hepatic inflammation and reduced the expression of pro-inflammatory cytokines in livers of wild type mice. In contrast, in livers of AKO mice, the same treatment induced severe hepatomegaly and microvesicular hepatosteatosis, and caused abnormal accumulation of fatty acyl CoA, glycogen, and their intermediate metabolites. Compared to wild type littermates, the anti-inflammatory and the mitochondria-stimulatory activity of rosiglitazone were largely attenuated in AKO mice. Replenishment with either adiponectin or uncoupling protein 2 (UCP2) significantly reduced fatty acyl CoA accumulation and increased mitochondrial activities in livers of rosiglitazone-treated AKO mice. In addition, adiponectin, but not UCP2, promoted the activation of glycogen synthase kinase 3beta (GSK3beta), a key molecule involved in regulating glycogen homeostasis.

CONCLUSIONS

Rosiglitazone elicits its protective functions against NAFLD largely through the induction of adiponectin, which prevents mitochondria stresses by promoting GSK3beta activation and UCP2 upregulation, two pathways coordinating the glucose and lipid metabolism in liver.

An anatomical and temporal portrait of physiological substrates for fatty acid amide hydrolase

Fatty acid amide hydrolase (FAAH) regulates amidated lipid transmitters, including the endocannabinoid anandamide and its N-acyl ethanolamine (NAE) congeners and transient receptor potential channel agonists N-acyl taurines (NATs). Using both the FAAH inhibitor PF-3845 and FAAH(-/-) mice, we present a global analysis of changes in NAE and NAT metabolism caused by FAAH disruption in central and peripheral tissues. Elevations in anandamide (and other NAEs) were tissue dependent, with the most dramatic changes occurring in brain, testis, and liver of PF-3845-treated or FAAH(-/-) mice. Polyunsaturated NATs accumulated to very high amounts in the liver, kidney, and plasma of these animals. The NAT profile in brain tissue was markedly different and punctuated by significant increases in long-chain NATs found exclusively in FAAH(-/-), but not in PF-3845-treated animals. Suspecting that this difference might reflect a slow pathway for NAT biosynthesis, we treated mice chronically with PF-3845 for 6 days and observed robust elevations in brain NATs. These studies, taken together, define the anatomical and temporal features of FAAH-mediated NAE and NAT metabolism, which are complemented and probably influenced by kinetically distinguishable biosynthetic pathways that produce these lipids in vivo.

Altered intramuscular lipid metabolism relates to diminished insulin action in men, but not women, in progression to diabetes

Whether sex differences in intramuscular triglyceride (IMTG) metabolism underlie sex differences in the progression to diabetes are unknown. Therefore, the current study examined IMTG concentration and fractional synthesis rate (FSR) in obese men and women with normal glucose tolerance (NGT) vs. those with prediabetes (PD). PD (n = 13 men and 7 women) and NGT (n = 7 men and 12 women) groups were matched for age and anthropometry. Insulin action was quantified using a hyperinsulinemic-euglycemic clamp with infusion of [6,6-(2)H(2)]-glucose. IMTG concentration was measured by gas chromatography/mass spectrometry (GC/MS) and FSR by GC/combustion isotope ratio MS (C-IRMS), from muscle biopsies taken after infusion of [U-(13)C]palmitate during 4 h of rest. In PD men, the metabolic clearance rate (MCR) of glucose was lower during the clamp (4.71 ± 0.77 vs. 8.62 ± 1.26 ml/kg fat-free mass (FFM)/min, P = 0.04; with a trend for lower glucose rate of disappearance (Rd), P = 0.07), in addition to higher IMTG concentration (41.2 ± 5.0 vs. 21.2 ± 3.4 µg/mg dry weight, P ≤ 0.01), lower FSR (0.21 ± 0.03 vs. 0.42 ± 0.06 %/h, P ≤ 0.01), and lower oxidative capacity (P = 0.03) compared to NGT men. In contrast, no difference in Rd, IMTG concentration, or FSR was seen in PD vs. NGT women. Surprisingly, glucose Rd during the clamp was not different between NGT men and women (P = 0.25) despite IMTG concentration being higher (42.6 ± 6.1 vs. 21.2 ± 3.4 µg/mg dry weight, P = 0.03) and FSR being lower (0.23 ± 0.04 vs. 0.42 ± 0.06 %/h, P = 0.02) in women. Alterations in IMTG metabolism relate to diminished insulin action in men, but not women, in the progression toward diabetes.

Inflexibility in intramuscular triglyceride fractional synthesis distinguishes prediabetes from obesity in humans

Whether intramuscular triglyceride (IMTG) concentration or flux is more important in the progression to type 2 diabetes is controversial. Therefore, this study examined IMTG concentration, as well as its fractional synthesis rate (FSR), in obese people with normal glucose tolerance (NGT; n = 20) vs. obese people with prediabetes (PD; n = 19), at rest and during exercise. Insulin action and secretion were assessed using an intravenous glucose tolerance test. [U-(13)C]palmitate was infused for 4 h before and throughout 1.5 h of treadmill walking at 50% VO(2(max)). IMTG concentration was measured by gas chromatograph/mass spectrometer, and FSR by gas chromatography-combustion isotope ratio mass spectrometer, from muscle biopsies taken immediately before and after exercise. Basal IMTG concentration was higher (43 +/- 5.7 vs. 27 +/- 3.9 mg/mg dry weight, P = 0.03) and FSR trended lower (0.23 +/- 0.04 vs. 0.32 +/- 0.05/h, P = 0.075), as did insulin action (S(i); 2.9 +/- 0.43 vs. 3.3 +/- 0.35 x 10(-4)/mU/ml, P = 0.07), in PD vs. NGT. IMTG concentration did not change significantly during exercise, but was no longer different in PD vs. NGT (45 +/- 7.7 vs. 37 +/- 5.8 mg/mg dry weight, P = 0.41). IMTG FSR suppressed during exercise in NGT (-81% to 0.06 +/- 0.13/h, P = 0.02), but not PD (+4% to 0.24 +/- 0.13%/h, P = 0.95). Palmitate oxidation was similar during rest (P = 0.92) and exercise (P = 0.94) between groups, but its source appeared different with more coming from muscle at rest and plasma during exercise in NGT, whereas the converse was true in PD. Altogether, higher basal IMTG concentration that is metabolically inflexible distinguishes obese people with PD from those with NGT.

Increased intramuscular lipid synthesis and low saturation relate to insulin sensitivity in endurance-trained athletes

Intramuscular triglyceride (IMTG) has received considerable attention as a potential mechanism promoting insulin resistance. Endurance-trained athletes have high amounts of IMTG but are insulin sensitive, suggesting IMTG content alone does not change insulin action. Recent data suggest increased muscle lipid synthesis protects against fat-induced insulin resistance. We hypothesized that rates of IMTG synthesis at rest would be increased in athletes compared with controls. Eleven sedentary men and 11 endurance-trained male cyclists participated in this study. An intravenous glucose tolerance test was performed to assess insulin action. After 3 days of dietary control and an overnight fast, [13C16]palmitate was infused at 0.0174 micromol.kg(-1).min(-1) for 4 h, followed by a muscle biopsy to measure isotope incorporation into IMTG and diacylglycerol. Compared with controls, athletes were twice as insulin sensitive (P=0.004) and had a significantly greater resting IMTG concentration (athletes: 20.4+/-1.6 microg IMTG/mg dry wt, controls: 14.5+/-1.8 microg IMTG/mg dry wt, P=0.04) and IMTG fractional synthesis rate (athletes: 1.56+/-0.37%/h, controls: 0.61+/-0.15%/h, P=0.03). Stearoyl-CoA desaturase 1 mRNA expression (P=0.02) and protein content (P=0.03) were also significantly greater in athletes. Diacylglycerol, but not IMTG, saturation was significantly less in athletes compared with controls (P=0.002). These data indicate endurance-trained athletes have increased synthesis rates of skeletal muscle IMTG and decreased saturation of skeletal muscle diacylglycerol. Increased synthesis rates are not due to recovery from exercise and are likely adaptations to chronic endurance exercise training.

Intramuscular lipid metabolism in the insulin resistance of smoking

OBJECTIVE

Smoking decreases insulin action and increases the risk of type 2 diabetes in humans. Mechanisms responsible for smoking-induced insulin resistance are unclear. We hypothesized smokers would have increased intramuscular triglyceride (IMTG) and diacylglycerol (DAG) concentration and decreased fractional synthesis rate (FSR) compared with nonsmokers.

RESEARCH DESIGN AND METHODS

Nonsmokers (n = 18, aged 20 +/- 0.5 years, BMI 22 +/- 0.4 kg/m(2), body fat 20 +/- 2%, 0 cigarettes per day) and smokers (n = 14, aged 21 +/- 0.7 years, BMI 23 +/- 0.4 kg/m(2), body fat 20 +/- 3%, 18 +/- 0.7 cigarettes per day) were studied in a fasted condition after a standardized diet. [U-(13)C]palmitate was infused during 4 h of rest followed by a skeletal muscle biopsy and intravenous glucose tolerance test.

RESULTS

Smokers were less insulin sensitive (S(i)) compared with nonsmokers (S(i) 5.28 +/- 0.5 nonsmokers vs. 3.74 +/- 0.3 smokers 10(-4) x microU(-1) x ml(-1), P = 0.03). There were no differences in IMTG or DAG concentration (IMTG 24.2 +/- 3.4 nonsmokers vs. 27.2 +/- 5.9 smokers microg/mg dry wt, DAG 0.34 +/- 0.02 nonsmokers vs. 0.35 +/- 0.02 smokers microg/mg dry wt) or IMTG FSR between groups (0.66 +/- 0.1 nonsmokers vs. 0.55 +/- 0.09 smokers %/hr). Intramuscular lipid composition was different, with increased percent saturation of IMTG (32.1 +/- 1.2 nonsmokers vs. 35.2 +/- 1.0 smokers %, P = 0.05) and DAG (52.8 +/- 1.7 nonsmokers vs. 58.8 +/- 2.2 smokers %, P = 0.04) in smokers. Smokers had significantly decreased peroxisome proliferator-activated receptor-gamma (1.76 +/- 0.1 nonsmokers vs. 1.42 +/- 0.11 smokers arbitrary units [AU], P = 0.03) and increased monocyte chemotactic protein-1 (3.11 +/- 0.41 nonsmokers vs. 4.83 +/- 0.54 smokers AU, P = 0.02) mRNA expression compared with nonsmokers. We also found increased insulin receptor substrate-1 Ser(636) phosphorylation in smokers compared with nonsmokers (0.73 +/- 0.08 nonsmokers vs. 1.14 +/- 0.09 smokers AU, P = 0.002).

CONCLUSIONS

These data suggest: 1) IMTG concentration and turnover are not related to alterations in insulin action in smokers compared to nonsmokers, 2) increased saturation of IMTG and DAG in skeletal muscle may be related to insulin action, and 3) basal inhibition of insulin receptor substrate-1 may decrease insulin action in smokers.

Deleterious action of FA metabolites on ATP synthesis: possible link between lipotoxicity, mitochondrial dysfunction, and insulin resistance

Insulin resistance is a characteristic feature of type 2 diabetes and obesity. Insulin-resistant individuals manifest multiple disturbances in free fatty acid (FFA) metabolism and have excessive lipid accumulation in insulin target tissues. Although much evidence supports a causal role for altered FFA metabolism in the development of insulin resistance, i.e., "lipotoxicity", the intracellular mechanisms by which elevated plasma FFA levels cause insulin resistance have yet to be completely elucidated. Recent studies have implicated a possible role for mitochondrial dysfunction in the pathogenesis of insulin resistance in skeletal muscle. We examined the effect of FFA metabolites [palmitoyl carnitine (PC), palmitoyl-coenzyme A (CoA), and oleoyl-CoA] on ATP synthesis in mitochondria isolated from mouse and human skeletal muscle. At concentrations ranging from 0.5 to 2 microM, these FFA metabolites stimulated ATP synthesis; however, above 5 microM, there was a dose-response inhibition of ATP synthesis. Furthermore, 10 microM PC inhibits ATP synthesis from pyruvate. Elevated PC concentrations (> or =10 microM) inhibit electron transport chain activity and decrease the mitochondrial inner membrane potential. These acquired mitochondrial defects, caused by a physiological increase in the concentration of FFA metabolites, provide a mechanistic link between lipotoxicity, mitochondrial dysfunction, and muscle insulin resistance.

Shotgun lipidomics reveals the temporally dependent, highly diversified cardiolipin profile in the mammalian brain: temporally coordinated postnatal diversification of cardiolipin molecular species with neuronal remodeling

Large-scale neuronal remodeling through apoptosis occurs shortly after birth in all known mammalian species. Apoptosis, in large part, depends upon critical interactions between mitochondrial membranes and cytochrome c. Herein, we examined the hypothesis that the large-scale reorganization of neuronal circuitry after birth is accompanied by profound alterations in cardiolipin (CL) content and molecular species distribution. During embryonic development, over 100 CL molecular species were identified and quantitated in murine neuronal tissues. The embryonic CL profile was notable for the presence of abundant amounts of relatively short aliphatic chains (e.g., palmitoleic and oleic acids). In sharp contrast, after birth, the CL profile contained a remarkably complex repertoire of CL molecular species, in which the signaling fatty acids (i.e., arachidonic and docosahexaenoic acids) were markedly increased. These results identify the rapid remodeling of CL in the perinatal period with resultant alterations in the physical properties of the mitochondrial membrane. The complex distribution of aliphatic chains in the neuronal CL pool is separate and distinct from that in other organs (e.g., heart, liver, etc.), where CL molecular species contain predominantly only one major type of aliphatic chain (e.g., linoleic acid). Analyses of mRNA levels by real-time quantitative polymerase chain reactions suggested that the alterations in CL content were due to the combined effects of both attenuation of de novo CL biosynthesis and decreased remodeling of CL. Collectively, these results provide a new perspective on the complexity of CL in neuronal signaling, mitochondrial bioenergetics, and apoptosis.

Quantitation of fatty acyl-coenzyme As in mammalian cells by liquid chromatography-electrospray ionization tandem mass spectrometry

Fatty acyl-CoAs participate in numerous cellular processes. This article describes a method for the quantitation of subpicomole amounts of long-chain and very-long-chain fatty acyl-CoAs by reverse-phase LC combined with electrospray ionization tandem mass spectrometry in positive ion mode with odd-chain-length fatty acyl-CoAs as internal standards. This method is applicable to a wide range of species [at least myristoyl- (C14:0-) to cerotoyl- (C26:0-) CoA] in modest numbers of cells in culture ( approximately 10(6)-10(7)), with analyses of RAW264.7 cells and MCF7 cells given as examples. Analysis of these cells revealed large differences in fatty acyl-CoA amounts (12 +/- 1.0 pmol/10(6) RAW264.7 cells vs. 80.4 +/- 6.1 pmol/10(6) MCF7 cells) and subspecies distribution. Very-long-chain fatty acyl-CoAs with alkyl chain lengths > C20 constitute <10% of the total fatty acyl-CoAs of RAW264.7 cells versus >50% for MCF7 cells, which somewhat astonishingly contain approximately as much C24:0- and C26:0-CoAs as C16:0- and C18:0-CoAs and essentially equal amounts of C26:1- and C18:1-CoAs. This simple and robust method should facilitate the inclusion of this family of compounds in "lipidomics" and "metabolomics" studies.

Low liver conversion rate of alpha-linolenic to docosahexaenoic acid in awake rats on a high-docosahexaenoate-containing diet

We quantified the rates of incorporation of alpha-linolenic acid (alpha-LNA; 18:3n-3) into "stable" lipids (triacylglycerol, phospholipid, cholesteryl ester) and the rate of conversion of alpha-LNA to docosahexaenoic acid (DHA; 22: 6n-3) in the liver of awake male rats on a high-DHA-containing diet after a 5-min intravenous infusion of [1-(14)C]alpha-LNA. At 5 min, 72.7% of liver radioactivity (excluding unesterified fatty acid radioactivity) was in stable lipids, with the remainder in the aqueous compartment. Using our measured specific activity of liver alpha-LNA-CoA, in the form of the dilution coefficient lambda(alpha-LNA-CoA), we calculated incorporation rates of unesterified alpha-LNA into liver triacylglycerol, phospholipid, and cholesteryl ester as 2,401, 749, and 9.6 nmol/s/g x 10(-4), respectively, corresponding to turnover rates of 3.2, 8.7, and 2.9%/min and half-lives of 8-24 min. A lower limit for the DHA synthesis rate from alpha-LNA equaled 15.8 nmol/s/g x 10(-4) (0.5% of the net in corporation rate). Thus, in rats on a high-DHA-containing diet, rates of beta-oxidation and esterification of alpha-LNA into stable liver lipids are high, whereas its conversion to DHA is comparatively low and insufficient to supply significant DHA to the brain. High incorporation and turnover rates likely reflect a high secretion rate by liver of stable lipids within very low density lipoproteins.

Analysis of medium-chain acyl-coenzyme A esters in mouse tissues by liquid chromatography-electrospray ionization mass spectrometry

Medium-chain acyl-coenzyme A (CoA) esters are key metabolites in lipid metabolism. Liquid chromatography-electrospray ionization mass spectrometry analysis of medium-chain acyl-CoA esters is described. Eight medium-chain acyl-CoA esters were well separated on a C(8)-MS reversed-phase column using a linear gradient of ammonium acetate buffer (pH 5.3)-acetonitrile. The positive-ion mass spectra of all the saturated and unsaturated medium-chain acyl-CoA esters gave dominant [M+H](+) ions, whereas their negative-ion mass spectra showed abundant [M-H](-) and [M-2H](2-) ions. The positive-ion mode of operation was slightly less sensitive than the negative-ion detection mode. Five medium-chain acyl-CoA esters of C(6:0), C(8:0), C(8:1), C(10:0), and C(10:1) in liver, heart, kidney, and brain from the mouse were identified. The predominant acyl-CoA peaks were C(6:0), C(8:0), and C(10:0). Small amounts of medium-chain acyl-CoAs of C(8:1) and C(10:1) were detected only in heart and kidney. The analytical method is very useful for the analysis of medium-chain acyl-CoA esters in the tissues.

LC/MS/MS Method for Quantitative Determination of Long-Chain Fatty Acyl-CoAs

Long-chain acyl-CoA esters (LCACoAs) are activated lipid species that represent key substrates in lipid metabolism. The relationship between lipid metabolism disorders and type 2 diabetes has attracted much attention to this class of metabolites. This paper presents a highly sensitive and robust on-line LC/MS(2) procedure for quantitative determination of LCACoAs from rat liver. A fast SPE method has been developed without the need for time-consuming evaporation steps for sample preparation. LCACoAs were separated with high resolution using a C18 reversed-phase column at high pH (10.5) with an ammonium hydroxide and acetonitrile gradient. Five LCACoAs (C16:0, C16:1, C18:0 C18:1, C18:2) were quantified by selective multireaction monitoring using a triple quadrupole mass spectrometer in positive electrospray ionization mode. It is possible to perform a neutral loss scan of 507 for lipid profiling of complex LCACoA mixtures in tissue extracts. The method presented was validated according to ICH guidelines for quantitative determination of five LCACoAs for physiological concentrations in 100-200 mg of tissue with accuracies ranging from 94.8 to 110.8%, interrun precisions between 2.6 and 12.2%, and intrarun precisions between 1.2 and 4.4%. Due to the high sensitivity of the developed method, the amount of tissue biopsied for reliable quantification can be reduced. This may be advantageous in the quantification of LCACoAs in humans.

Determination of long-chain fatty acid acyl-coenzyme A compounds using liquid chromatography-electrospray ionization tandem mass spectrometry

Acyl-CoAs have important role in fat and glucose metabolism of the cells. In this study we have developed an on-line HPLC-ESI-MS/MS method for determination of long-chain acyl-CoA compounds in rat liver samples. Six long-chain acyl-CoAs (C16:0, C16:1, C18:0, C18:1, C20:0 and C20:4) were separated with a C4 reversed-phase column using triethylamine acetate and acetonitrile gradient. Negative electrospray ionization is very suitable for acyl-CoA compounds and excellent MS/MS spectra for long-chain acyl-CoAs can be obtained. MS/MS method with an ion trap mass spectrometer makes it possible to identify and quantitate individual acyl-CoAs simultaneously. The method proved to be sensitive enough for determination of all compounds of interest using 0.4-0.7 g of tissue and was validated in the range of 0.1-15.0 pmol/microl.

Isolation of a Gene Encoding a 1,2-Diacylglycerol-sn-acetyl-CoA Acetyltransferase from Developing Seeds of Euonymus alatus

1,2-Diacyl-3-acetyl-sn-glycerols (ac-TAG) are unusual triacylglycerols that constitute the major storage lipid in the seeds of Euonymus alatus (Burning Bush). These ac-TAGs have long-chain acyl groups esterified at both the sn-1 and sn-2 positions of glycerol. Cell-free extracts of developing seeds of E. alatus contain both long-chain acyl-CoA and acetyl-CoA sn-1,2-diacylglycerol acyltransferase (DGAT) activity. We have isolated a gene from developing seeds of Euonymus alatus that shows a very high sequence similarity to the members of the DGAT1 gene family (i.e. related to acyl-CoA:cholesterol acyltransferases). This Euonymus DGAT1 gene, when expressed in wild type yeast, results in a 5-fold enhancement of long-chain triacylglycerol (lc-TAG) accumulation, as well as the appearance of low levels of ac-TAG. Hydrogenated ac-TAG molecular species were identified by gas chromatography-mass spectrometry. Microsomes isolated from this transformed yeast show diacylglycerol:acetyl-CoA acetyltransferase activity, which is about 40-fold higher than that measured in microsomes prepared from yeast transformed with the empty vector or with the Arabidopsis thaliana DGAT1 gene. The specific activity of this microsomal acetyltransferase activity is of the same order of magnitude as the microsomal long-chain DGAT activities measured for yeast lines transformed with the empty vector or either the Arabidopsis or Euonymus DGAT1 genes. Despite this, ac-TAG accumulation in yeast transformed with the Euonymus DGAT1 gene was very low (0.26% of lc-TAG), whereas lc-TAG accumulation was enhanced. Possible reasons for this anomaly are discussed. Expression of the Euonymus DGAT1-like gene in yeast lines where endogenous TAG synthesis has been deleted confirmed that the gene product has both long-chain acyl- and acetyltransferase activity.

An improved method for tissue long-chain acyl-CoA extraction and analysis

We report an extensively modified method for the extraction, solid-phase purification, and HPLC analysis of long-chain acyl-CoAs from tissues. Tissue samples were homogenized in a glass homogenizer in KH2PO4 buffer (100 mM, pH 4.9) and again after the addition of 2-propanol. Acyl-CoAs were then extracted from the homogenate with acetonitrile (ACN). The acyl-CoAs in the extract were bound to an oligonucleotide purification column and eluted using 2-propanol. This eluent was concentrated and then loaded onto a C-18 column and eluted using a binary gradient system in which solvent A was KH2PO4 (75 mM, pH 4.9) and solvent B was ACN containing 600 mM glacial acetic acid. Initial flow rate was 0.5 or 0.25 ml/min depending upon the tissue used. The HPLC eluent was monitoring at 260 nm. Our modifications increased the recovery of the extraction procedure to 70-80%, depending upon tissue, with high reproducibility and significantly improved separation of the most common unsaturated and saturated acyl-CoAs. We also report, for the first time, the mass (nanomoles per gram wet weight) of the most common polyunsaturated acyl-CoAs in rat heart, kidney, and muscle tissues. The modifications and high recovery permit the use of tissue samples of less than 100 mg, making this method useful for the analysis of small tissue amounts associated with mice.

Serine palmitoyltransferase, a key enzyme of sphingolipid metabolism

The first step in the biosynthesis of sphingolipids is the condensation of serine and palmitoyl CoA, a reaction catalyzed by serine palmitoyltransferase (SPT) to produce 3-ketodihydrosphingosine (KDS). This review focuses on recent advances in the biochemistry and molecular biology of SPT. SPT belongs to a family of pyridoxal 5'-phosphate (PLP)-dependent alpha-oxoamine synthases (POAS). Mammalian SPT is a heterodimer of 53-kDa LCB1 and 63-kDa LCB2 subunits, both of which are bound to the endoplasmic reticulum (ER) most likely with the type I topology, whereas other members of the POAS family are soluble homodimer enzymes. LCB2 appears to be unstable unless it is associated with LCB1. Potent inhibitors of SPT structurally resemble an intermediate in a probable multistep reaction mechanism for SPT. Although SPT is a housekeeping enzyme, its activity is regulated transcriptionally and post-transcriptionally, and its up-regulation is suggested to play a role in apoptosis induced by certain types of stress. Specific missense mutations in the human LCB1 gene cause hereditary sensory neuropathy type I, an autosomal dominantly inherited disease, and these mutations confer dominant-negative effects on SPT activity.

Acyl-CoA-binding protein in the armadillo Harderian gland: its primary structure and possible role in lipid secretion

Similar to those of other species, the Harderian glands of armadillo produce an abundant lipid secretion, most of which is composed of 1-alkyl-2,3-diacylglycerol. Biosynthesis of this component is apparently performed with the participation of one cytosolic pool of acyl-CoA and another of free fatty acids. The acyl-CoA-binding protein (ACBP) is present at a concentration at least 7-fold that of the heart-type fatty acid-binding protein (H-FABP), though lower than that in other armadillo organs such as liver and brain. The ACBP complete amino acid sequence was determined by Edman degradation of peptides generated by cleavage of the protein with cyanogen bromide, endopeptidase Glu-C, and trypsin. ACBP consists of 86 residues and has a calculated molecular mass of 9783 Da, taking into account that an acetyl group is blocking the N-terminus. Identity percentages between armadillo Harderian gland ACBP and other known ACBPs show that the protein belongs to the liver-specific ACBP isoform (L-ACBP). The fact that the ACBP concentration is higher than that of FABP suggests that the Harderian gland is able to store acyl-CoA amounts in ACBP larger than those of fatty acids in H-FABP for 1-alkyl-2,3-diacylglycerol synthesis.

Long-chain acyl-CoA esters as indicators of lipid metabolism and insulin sensitivity in rat and human muscle

Long-chain acyl-CoAs (LCACoA) are an activated lipid species that are key metabolites in lipid metabolism; they also have a role in the regulation of other cellular processes. However, few studies have linked LCACoA content in rat and human muscle to changes in nutritional status and insulin action. Fasting rats for 18 h significantly elevated the three major LCACoA species in muscle (P < 0.001), whereas high-fat feeding of rats with a safflower oil (18:2) diet produced insulin resistance and increased total LCACoA content (P < 0.0001) by specifically increasing 18:2-CoA. The LCACoA content of red muscle from rats (4-8 nmol/g) was 4- to 10-fold higher than adipose tissue (0.4-0.9 nmol/g, P < 0.001), suggesting that any contamination of muscle samples with adipocytes would contribute little to the LCACoA content of muscle. In humans, the LCACoA content of muscle correlated significantly with a measure of whole body insulin action in 17 male subjects (r(2) = 0.34, P = 0.01), supporting a link between muscle lipid metabolism and insulin action. These results demonstrate that the LCACoA pool reflects lipid metabolism and nutritional state in muscle. We conclude that the LCACoA content of muscle provides a direct index of intracellular lipid metabolism and its links to insulin action, which, unlike triglyceride content, is not subject to contamination by closely associated adipose tissue.

Role of acylCoA binding protein in acylCoA transport, metabolism and cell signaling

Long chain acylCoA esters (LCAs) act both as substrates and intermediates in intermediary metabolism and as regulators in various intracellular functions. AcylCoA binding protein (ACBP) binds LCAs with high affinity and is believed to play an important role in intracellular acylCoA transport and pool formation and therefore also for the function of LCAs as metabolites and regulators of cellular functions [1]. The major factors controlling the free concentration of cytosol long chain acylCoA ester (LCA) include ACBP [2], sterol carrier protein 2 (SCP2) [3] and fatty acid binding protein (FABP) [4]. Additional factors affecting the concentration of free LCA include feed back inhibition of the acylCoA synthetase [5], binding to acylCoA receptors (LCA-regulated molecules and enzymes), binding to membranes and the activity of acylCoA hydrolases [6].

Identification and quantitation of the fatty acids composing the CoA ester pool of bovine retina, heart, and liver

Several proteins found in retinal photoreceptor cells (guanylate cyclase activating protein, protein kinase A, recoverin, and transducin) are N-terminally modified with the fatty acids 12:0, 14:0, 14:1n-9, and 14:2n-6, whereas similar proteins in other tissues contain only 14:0. It has been hypothesized that the acyl-CoA pool of the retina contains amounts of 12:0, 14:1n-9, and 14:2n-6 elevated over 14:0, in comparison to other tissues, and this accounts for the specificity of N-terminal fatty acylation. To test this hypothesis, we performed fatty acid analysis on total acyl-CoAs purified from bovine retina (light-adapted), heart, and liver. We also examined the N- and S-linked fatty acid composition of the total protein pools from these tissues. Acyl-CoAs were prepared from heart, liver, and retina and separated by high performance liquid chromatography (HPLC). Identities of peaks were based on HPLC of standard 12:0, 14:0, 14:1n-9, and 14:2n-6 CoAs. Total protein was subjected to base hydrolysis followed by acidic methanolysis to release S- and N-linked fatty acids, respectively, and fatty acid phenacyl esters were prepared for HPLC analysis. Retina had levels of 12:0 (2.7 +/- 2.1%), 14:1n-9 (2.9 +/- 2.2%), and 14:2n-6 (1.6 +/- 0.7%) CoAs below that of 14:0 CoA (7.0 +/- 1.8%). Likewise, heart levels of 14:2n-6 CoA (3.7 +/- 0.1%) were near and 12:0 (2.6 +/- 0. 6%) and 14:1n-9 (0.7 +/- 0.3%) CoAs were below that of 14:0 CoA (3.8 +/- 1.0%). Liver had levels of 12:0 (16.1 +/- 5.7%) and 14:2n-6 (8.1 +/- 1.2%) CoAs above and 14:1n-9 CoA (1.2 +/- 0.6%) below that of 14:0 CoA (5.9 +/- 0.8%). Fatty acid analysis of total protein showed that all tissues contained S-linked 16:0, 18:0, and 18:1n-9. Retina proteins contained N-linked 14:0, 14:1n-9, and 14:2n-6, whereas heart and liver had only 14:0. Our findings do not support the hypothesis that the CoA ester pool of the retina is enriched with 12:0, 14:1n-9, and 14:2n-6 over 14:0, in comparison to other tissues. This suggests that alternative models must be considered for the regulation of N-terminal fatty acylation of proteins in photoreceptor cells.

Relation between free fatty acid and acyl-CoA concentrations in rat brain following decapitation

To ascertain effects of total ischemia on brain phospholipid metabolism, anesthetized rats were decapitated and unesterified fatty acids and long chain acyl-CoA concentrations were analyzed in brain after 3 or 15 min. Control brain was taken from rats that were microwaved. Fatty acids were quantitated by extraction, thin layer chromatography and gas chromatography. Long-chain acyl-CoAs were quantitated by solubilization, solid phase extraction with an oligonucleotide purification cartridge and HPLC. Unesterified fatty acid concentrations increased significantly after decapitation, most dramatically for arachidonic acid (76 fold at 15 min) followed by docosahexaenoic acid. Of the acyl-CoA molecular species only the concentration of arachidonoyl-CoA was increased at 3 min and 15 min after decapitation, by 3-4 fold compared with microwaved brain. The concentration of docosahexaenoyl-CoA fell whereas concentrations of the other acyl-CoAs were unchanged. The increase in arachidonoyl-CoA after decapitation indicates that reincorporation of arachidonic acid into membrane phospholipids is possible during ischemia, likely at the expense of docosahexaenoic acid.

Role of long-chain fatty acyl-CoA esters in the regulation of metabolism and in cell signalling

The intracellular concentration of free unbound acyl-CoA esters is tightly controlled by feedback inhibition of the acyl-CoA synthetase and is buffered by specific acyl-CoA binding proteins. Excessive increases in the concentration are expected to be prevented by conversion into acylcarnitines or by hydrolysis by acyl-CoA hydrolases. Under normal physiological conditions the free cytosolic concentration of acyl-CoA esters will be in the low nanomolar range, and it is unlikely to exceed 200 nM under the most extreme conditions. The fact that acetyl-CoA carboxylase is active during fatty acid synthesis (Ki for acyl-CoA is 5 nM) indicates strongly that the free cytosolic acyl-CoA concentration is below 5 nM under these conditions. Only a limited number of the reported experiments on the effects of acyl-CoA on cellular functions and enzymes have been carried out at low physiological concentrations in the presence of the appropriate acyl-CoA-buffering binding proteins. Re-evaluation of many of the reported effects is therefore urgently required. However, the observations that the ryanodine-senstitive Ca2+-release channel is regulated by long-chain acyl-CoA esters in the presence of a molar excess of acyl-CoA binding protein and that acetyl-CoA carboxylase, the AMP kinase kinase and the Escherichia coli transcription factor FadR are affected by low nanomolar concentrations of acyl-CoA indicate that long-chain acyl-CoA esters can act as regulatory molecules in vivo. This view is further supported by the observation that fatty acids do not repress expression of acetyl-CoA carboxylase or Delta9-desaturase in yeast deficient in acyl-CoA synthetase.

Barley lipid-transfer protein complexed with palmitoyl CoA: the structure reveals a hydrophobic binding site that can expand to fit both large and small lipid-like ligands

BACKGROUND

. Plant nonspecific lipid-transfer proteins (nsLTPs) bind a variety of very different lipids in vitro, including phospholipids, glycolipids, fatty acids and acyl coenzyme As. In this study we have determined the structure of a nsLTP complexed with palmitoyl coenzyme A (PCoA) in order to further our understanding of the structural mechanism of the broad specificity of these proteins and its relation to the function of nsLTPs in vivo.

RESULTS

. 1H and 13C nuclear magnetic resonance spectroscopy (NMR) have been used to study the complex between a nsLTP isolated from barley seeds (bLTP) and the ligand PCoA. The resonances of 97% of the 1H atoms were assigned for the complexed bLTP and nearly all of the resonances were assigned in the bound PCoA ligand. The palmitoyl chain of the ligand was uniformly 13C-labelled allowing the two ends of the hydrocarbon chain to be assigned. The comparison of a subset of 20 calculated structures to an average structure showed root mean square deviations of 1.89 +/- 0.19 for all C, N, O, P and S atoms of the entire complex and of 0.57 +/- 0.09 for the peptide backbone atoms of the four alpha helices of the complexed bLTP. The four-helix topology of the uncomplexed bLTP is maintained in the complexed form of the protein. The bLTP only binds the hydrophobic parts of PCoA with the rest of the ligand remaining exposed to the solvent. The palmitoyl chain moiety of the ligand is placed in the interior of the protein and bent in a U-shape. This part of the ligand is completely buried within a hydrophobic pocket of the protein.

CONCLUSIONS

. A comparison of the structures of bLTP in the free and bound forms suggests that bLTP can accommodate long olefinic ligands by expansion of the hydrophobic binding site. This expansion is achieved by a bend of one helix, HA, and by conformational changes in both the C terminus and helix HC. This mode of binding is different from that seen in the structure of maize nsLTP in complex with palmitic acid, where binding of the ligand is not associated with structural changes.

Acyl-CoA binding proteins: multiplicity and function

The physiological role of long-chain fatty acyl-CoA is thought to be primarily in intermediary metabolism of fatty acids. However, recent data show that nM to microM levels of these lipophilic molecules are potent regulators of cell functions in vitro. Although long-chain fatty acyl-CoA are present at several hundred microM concentration in the cell, very little long-chain fatty acyl-CoA actually exists as free or unbound molecules, but rather is bound with high affinity to membrane lipids and/or proteins. Recently, there is growing awareness that cytosol contains nonenzymatic proteins also capable of binding long-chain fatty acyl-CoA with high affinity. Although the identity of the cytosolic long-chain fatty acyl-CoA binding protein(s) has been the subject of some controversy, there is growing evidence that several diverse nonenzymatic cytosolic proteins will bind long-chain fatty acyl-CoA. Not only does acyl-CoA binding protein specifically bind medium and long-chain fatty acyl-CoA (LCFA-CoA), but ubiquitous proteins with multiple ligand specificities such as the fatty acid binding proteins and sterol carrier protein-2 also bind LCFA-CoA with high affinity. The potential of these acyl-CoA binding proteins to influence the level of free LCFA-CoA and thereby the amount of LCFA-CoA bound to regulatory sites in proteins and enzymes is only now being examined in detail. The purpose of this article is to explore the identity, nature, function, and pathobiology of these fascinating newly discovered long-chain fatty acyl-CoA binding proteins. The relative contributions of these three different protein families to LCFA-CoA utilization and/or regulation of cellular activities are the focus of new directions in this field.

Oligomerization of VIP21-caveolin in vitro is stabilized by long chain fatty acylation or cholesterol

VIP21-caveolin is one of the components which form the cytoplasmic surface of caveolae. In vivo, this integral membrane protein is found in homo-oligomers with molecular masses of approximately 200, 400 and 600 kDa. These oligomers are also formed by the addition of cytosol to the in vitro synthesized and membrane inserted VIP21-caveolin. Here we show that long chain fatty acyl coenzyme A esters can completely substitute for cytosol in inducing 200 kDa and 400 kDa complexes, whereas 25-hydroxy-cholesterol can produce the 200 kDa oligomer. In order to understand whether acylation of VIP21-caveolin itself is a prerequisite for oligomerization, we studied a mutant protein lacking all three cysteines. When analyzed by velocity sucrose gradient centrifugation in the presence of the non-ionic detergent octylglucoside, both palmitoylated and non-palmitoylated VIP21-caveolin formed oligomers that were indistinguishable. However, only the oligomers of the non-palmitoylated protein are disrupted when analyzed by SDS-PAGE without boiling. These data suggest that the protein domains of VIP21-caveolin are the primary determinants of oligomerization, but that palmitoylation of cysteine residues can increase the stability of the oligomers.

Fatty acyl-CoA oxidase activity is induced before long-chain acyl-CoA hydrolase activity and acyl-CoA binding protein in liver of rat treated with peroxisome proliferating 3-thia fatty acids

1. In this study we explored the relationship between specific acyl-CoA esters and induction of acyl-CoA binding protein (ACBP) and enzymes related to the proliferation of peroxisomes. Male Wistar rats were administered a single dose (150 mg/day/kg) of sulphur-substituted fatty acid analogues, and the effects of tetradecylthioacetic acid and 3-thiadicarboxylic acid, which both act as peroxisome proliferators, were compared with the effects of tetradecylthiopropionic acid and palmitic acid which do not induce peroxisome proliferation. 2. The hepatic level of total long-chain acyl-CoA was significantly increased within 12 h of feeding these fatty acids, except in rat fed tetradecylthioacetic acid. Hplc chromatograms of liver extracts prepared from rat fed tetradecylthioacetic acid showed that tetradecylthioacetyl-CoA ester accumulated in the liver 4 h after feeding and had disappeared after 24 h. In liver extracts of the tetradecylthiopropionic acid-treated rat tetradecylthiopropionyl-CoA was not observed, but the appearance of a new long-chain acyl-CoA ester, probably a metabolite of tetradecylthiopropionic acid, was detected. This new peak reached a maximum 4h after feeding. In rat fed tetradecylthioacetic acid and 3-thiadicarboxylic acid the hepatic level of fatty acyl-CoA oxidase mRNA increased 8 h after feeding, while the acyl-CoA oxidase activity had increased after 12 h. 3. The early accumulation of specific tetradecylthioacetyl-CoA suggests that this ester may be a possible mediator of the induction of fatty acyl-CoA oxidase. The level of hepatic acyl-CoA binding protein, long-chain acyl-CoA hydrolase activity and long-chain acyl-CoA synthetase activity did not change after a single dose of all four fatty acids. Prolonged administration of 3-thia fatty acids resulted, however, in a dose- and time-dependent increase in hepatic ACBP content and ACBP mRNA level. The amount of ACBP increased in parallel to the long-chain acyl-CoA hydrolase activity. The correlated induction of fatty acyl-CoA binding protein and long-chain acyl-CoA hydrolase seems to be dependent on a sustained accumulation of total long-chain acyl-CoA esters.

Interaction of acyl-CoA binding protein (ACBP) on processes for which acyl-CoA is a substrate, product or inhibitor

It is shown that acyl-CoA binding protein (ACBP), in contrast with fatty acid binding protein (FABP), stimulates the synthesis of long-chain acyl-CoA esters by mitochondria. ACBP effectively opposes the product feedback inhibition of the long-chain acyl-CoA synthetase by sequestration of the synthesized acyl-CoA esters. Feedback inhibition of microsomal long-chain acyl-CoA synthesis could not be observed, due to the formation of small acyl-CoA binding vesicles during preparation and/or incubation. Microsomal membrane preparations are therefore unsuitable for studying feedback inhibition of long-chain acyl-CoA synthesis. ACBP was found to have a strong attenuating effect on the long-chain acyl-CoA inhibition of both acetyl-CoA carboxylase and mitochondrial adenine nucleotide translocase. Both processes were unaffected by the presence of long-chain acyl-CoA esters when the ratio of long-chain acyl-CoA to ACBP was below 1, independent of the acyl-CoA concentration used. It is therefore not the acyl-CoA concentration as such which is important from a regulatory point of view, but the ratio of acyl-CoA to ACBP. The cytosolic ratio of long-chain acyl-CoA to ACBP was shown to be well below 1 in the liver of fed rats. ACBP could compete with the triacylglycerol-synthesizing pathway, but not with the phospholipid-synthesizing enzymes, for acyl-CoA esters. Furthermore, in contrast with FABP, ACBP was able to protect long-chain acyl-CoA esters against hydrolysis by microsomal acyl-CoA hydrolases. The results suggest that long-chain acyl-CoA esters synthesized for either triacylglycerol synthesis or beta-oxidation have to pass through the acyl-CoA/ACBP pool before utilization. This means that acyl-CoA synthesized by microsomal or mitochondrial synthetases is uniformly available in the cell. It is suggested that ACBP has a duel function in (1) creating a cytosolic pool of acyl-CoA protected against acyl-CoA hydrolases, and (2) protecting vital cellular processes from being affected by long-chain acyl-CoA esters.

Effect of heterologous expression of acyl-CoA-binding protein on acyl-CoA level and composition in yeast

We have expressed a bovine synthetic acyl-CoA-binding protein (ACBP) gene in yeast (Saccharomyces cerevisiae) under the control of the GAL1 promoter. The heterologously expressed bovine ACBP constituted up to 6.4% of total cellular protein and the processing was identical with that of native bovine ACBP, i.e. the initiating methionine was removed and the following serine residue was N-acetylated. The expression of this protein did not affect the growth rate of the cells. Determination of the yeast acyl-CoA pool size showed a close positive correlation between the ACBP content of the cells and the size of the acyl-CoA pool. Thus ACBP can act as an intracellular acyl-CoA pool former. Possible physiological functions of ACBP in cells are discussed.