Lignoceroyl-CoA ligase activity in rat brain microsomal fraction: topographical localization and effect of detergents and alpha-cyclodextrin

Peroxisomal acyl-CoA synthetases

Peroxisomes carry out many essential lipid metabolic functions. Nearly all of these functions require that an acyl group-either a fatty acid or the acyl side chain of a steroid derivative-be thioesterified to coenzyme A (CoA) for subsequent reactions to proceed. This thioesterification, or "activation", reaction, catalyzed by enzymes belonging to the acyl-CoA synthetase family, is thus central to cellular lipid metabolism. However, despite our rather thorough understanding of peroxisomal metabolic pathways, surprisingly little is known about the specific peroxisomal acyl-CoA synthetases that participate in these pathways. Of the 26 acyl-CoA synthetases encoded by the human and mouse genomes, only a few have been reported to be peroxisomal, including ACSL4, SLC27A2, and SLC27A4. In this review, we briefly describe the primary peroxisomal lipid metabolic pathways in which fatty acyl-CoAs participate. Then, we examine the evidence for presence and functions of acyl-CoA synthetases in peroxisomes, much of which was obtained before the existence of multiple acyl-CoA synthetase isoenzymes was known. Finally, we discuss the role(s) of peroxisome-specific acyl-CoA synthetase isoforms in lipid metabolism.

Nutritional significance and metabolism of very long chain fatty alcohols and acids from dietary waxes

Very long chain fatty alcohols obtained from plant waxes and beeswax have been reported to lower plasma cholesterol in humans. This review discusses nutritional or regulatory effects produced by wax esters or aliphatic acids and alcohols found in unrefined cereal grains, beeswax, and many plant-derived foods. Reports suggest that 5-20 mg per day of mixed C24-C34 alcohols, including octacosanol and triacontanol, lower low-density lipoprotein (LDL) cholesterol by 21%-29% and raise high-density lipoprotein cholesterol by 8%-15%. Wax esters are hydrolyzed by a bile salt-dependent pancreatic carboxyl esterase, releasing long chain alcohols and fatty acids that are absorbed in the gastrointestinal tract. Studies of fatty alcohol metabolism in fibroblasts suggest that very long chain fatty alcohols, fatty aldehydes, and fatty acids are reversibly inter-converted in a fatty alcohol cycle. The metabolism of these compounds is impaired in several inherited human peroxisomal disorders, including adrenoleukodystrophy and Sjögren-Larsson syndrome. Reports on dietary management of these diseases confirm that very long chain fatty acids (VLCFA) are normal constituents of the human diet and are synthesized endogenously. Concentrations of VLCFA in blood plasma increase during fasting and when children are placed on ketogenic diets to suppress seizures. Existing data support the hypothesis that VLCFA exert regulatory roles in cholesterol metabolism in the peroxisome and also alter LDL uptake and metabolism.

TNFalpha downregulates PPARdelta expression in oligodendrocyte progenitor cells: implications for demyelinating diseases

TNFalpha has been implicated in several demyelinating disorders, including multiple sclerosis (MS) and X-adrenoleukodystrophy (X-ALD). TNFalpha abundance is greatly increased in the areas surrounding damaged regions of the central nervous system of patients with MS and X-ALD, but its role in the observed demyelination remains to be elucidated. A class of nuclear receptors, the peroxisome proliferator-activated receptors (PPARs), has been implicated in several physiological and pathological processes. In particular, PPARdelta has been shown to promote oligodendrocyte (OL) survival and differentiation and PPARgamma has been implicated in inflammation. In the present study, we investigate on the effects of TNFalpha on OLs during differentiation in vitro. The results obtained show that TNFalpha treatment impairs PPARdelta expression with concomitant decrease of lignocerolyl-CoA synthase and very-long-chain fatty acid beta-oxidation as well as plasmalogen biosynthesis. We propose a hypothetical model possibly explaining the perturbation effects of proinflammatory cytokines on myelin synthesis, maturation, and turnover.

Molecular characterization of an Arabidopsis acyl-coenzyme a synthetase localized on glyoxysomal membranes

In higher plants, fat-storing seeds utilize storage lipids as a source of energy during germination. To enter the beta-oxidation pathway, fatty acids need to be activated to acyl-coenzyme As (CoAs) by the enzyme acyl-CoA synthetase (ACS; EC 6.2.1.3). Here, we report the characterization of an Arabidopsis cDNA clone encoding for a glyoxysomal acyl-CoA synthetase designated AtLACS6. The cDNA sequence is 2,106 bp long and it encodes a polypeptide of 701 amino acids with a calculated molecular mass of 76,617 D. Analysis of the amino-terminal sequence indicates that acyl-CoA synthetase is synthesized as a larger precursor containing a cleavable amino-terminal presequence so that the mature polypeptide size is 663 amino acids. The presequence shows high similarity to the typical PTS2 (peroxisomal targeting signal 2). The AtLACS6 also shows high amino acid identity to prokaryotic and eukaryotic fatty acyl-CoA synthetases. Immunocytochemical and cell fractionation analyses indicated that the AtLACS6 is localized on glyoxysomal membranes. AtLACS6 was overexpressed in insect cells and purified to near homogeneity. The purified enzyme is particularly active on long-chain fatty acids (C16:0). Results from immunoblot analysis revealed that the expression of both AtLACS6 and beta-oxidation enzymes coincide with fatty acid degradation. These data suggested that AtLACS6 might play a regulatory role both in fatty acid import into glyoxysomes by making a complex with other factors, e.g. PMP70, and in fatty acid beta-oxidation activating the fatty acids.

Identification of the pathway of alpha-oxidation of cerebronic acid in peroxisomes

Cerebronic acid (2-hydroxytetracosanoic acid), an alpha-hydroxy very long-chain fatty acid (VLCFA) and a component of cerebrosides and sulfatides, is unique to nervous tissues. Studies were carried out to identify the pathway and the subcellular site involved in the oxidation of cerebronic acid. The results from these studies revealed that cerebronic acid was catabolized by alpha-oxidation to CO2 and tricosanoic acid (23:0). Studies with subcellular fractions indicated that cerebronic acid was alpha-oxidized in fractions having particulate bound catalase and enzyme systems for the beta-oxidation of VLCFA (e.g., lignoceric acid), suggesting peroxisomes as the subcellular organelle responsible for alpha-oxidation of cerebronic acid. Etomoxir, an inhibitor of mitochondrial fatty acid oxidation, had no effect on cerebronic acid alpha-oxidation. Further, cerebronic acid oxidation was found to be dependent on the presence of NAD+ but not FAD, NADPH, ATP, Mg2+, or CoASH. Intraorganellar localization studies indicated that the enzyme system for the alpha-oxidation of cerebronic acid was associated with the peroxisomal limiting membranes. Studies on cultured fibroblasts from normal subjects and patients with peroxisomal disorders indicated an impairment of alpha-oxidation of cerebronic acid in cell lines that lack peroxisomes [e.g., Zellweger syndrome (ZS)]. On the other hand, alpha-oxidation of cerebronic acid was found to be normal in cell lines from X-linked adrenoleukodystrophy, adult Refsum disease, and rhizomelic chondrodysplasia punctata. Our results clearly demonstrate that alpha-oxidation of alpha-hydroxy VLCFA (cerebronic acid) is a peroxisomal function and that this oxidation is impaired in ZS. Furthermore, this alpha-oxidation enzyme system is distinct from the one for the alpha-oxidation of beta-carbon branched-chain fatty acids (e.g., phytanic acid).

Intraperoxisomal localization of very-long-chain fatty acyl-CoA synthetase: implication in X-adrenoleukodystrophy

X-adrenoleukodystrophy (X-ALD) is a demyelinating disorder characterized by the accumulation of saturated very-long-chain (VLC) fatty acids (>C(22:0)) due to the impaired activity of VLC acyl-CoA synthetase (VLCAS). The gene responsible for X-ALD was found to code for a peroxisomal integral membrane protein (ALDP) that belongs to the ATP binding cassette superfamily of transporters. To understand the function of ALDP and how ALDP and VLCAS interrelate in the peroxisomal beta-oxidation of VLC fatty acids we investigated the peroxisomal topology of VLCAS protein. Antibodies raised against a peptide toward the C-terminus of VLCAS as well as against the N-terminus were used to define the intraperoxisomal localization and orientation of VLCAS in peroxisomes. Indirect immunofluorescent and electron microscopic studies show that peroxisomal VLCAS is localized on the matrix side. This finding was supported by protease protection assays and Western blot analysis of isolated peroxisomes. To further address the membrane topology of VLCAS, Western blot analysis of total membranes or integral membranes prepared from microsomes and peroxisomes indicates that VLCAS is a peripheral membrane-associated protein in peroxisomes, but an integral membrane in microsomes. Moreover, peroxisomes isolated from cultured skin fibroblasts from X-ALD patients with a mutation as well as a deletion in ALDP showed a normal amount of VLCAS. The consequence of VLCAS being localized to the luminal side of peroxisomes suggests that ALDP may be involved in stabilizing VLCAS activity, possibly through protein-protein interactions, and that loss or alterations in these interactions may account for the observed loss of peroxisomal VLCAS activity in X-ALD.

Increased peroxisomal fatty acid beta-oxidation and enhanced expression of peroxisome proliferator-activated receptor-alpha in diabetic rat liver

To determine whether the increased fatty acid beta-oxidation in the peroxisomes of diabetic rat liver is mediated by a common peroxisome proliferation mechanism, we measured the activation of long-chain (LC) and very long chain (VLC) fatty acids catalyzed by palmitoyl CoA ligase (PAL) and lignoceryl CoA ligase and oxidation of LC (palmitic acid) and VLC (lignoceric acid) fatty acids by isotopic methods. Immunoblot analysis of acyl-CoA oxidase (ACO), and Northern blot analysis of peroxisome proliferator-activated receptor (PPAR-alpha), ACO, and PAL were also performed. The PAL activity increased in peroxisomes and mitochondria from the liver of diabetic rats by 2.6-fold and 2.1 -fold, respectively. The lignoceroyl-CoA ligase activity increased by 2.6-fold in diabetic peroxisomes. Palmitic acid oxidation increased in the diabetic peroxisomes and mitochondria by 2.5-fold and 2.7-fold, respectively, while lignoceric acid oxidation increased by 2.0-fold in the peroxisomes. Immunoreactive ACO protein increased by 2-fold in the diabetic group. The mRNA levels for PPAR-alpha, ACO and PAL increased 2.9-, 2.8- and 1.6-fold, respectively, in the diabetic group. These results suggest that the increased supply of fatty acids to liver in diabetic state stimulates the expression of PPAR-alpha and its target genes responsible for the metabolism of fatty acids.

Biochemistry of peroxisomes in health and disease

The ubiquitous distribution of peroxisomes and the identification of a number of inherited diseases associated with peroxisomal dysfunction indicate that peroxisomes play an essential part in cellular metabolism. Some of the most important metabolic functions of peroxisomes include the synthesis of plasmalogens, bile acids, cholesterol and dolichol, and the oxidation of fatty acids (very long chain fatty acids > C22, branched chain fatty acids (e.g. phytanic acid), dicarboxylic acids, unsaturated fatty acids, prostaglandins, pipecolic acid and glutaric acid). Peroxisomes are also responsible for the metabolism of purines, polyamines, amino acids, glyoxylate and reactive oxygen species (e.g. O-2 and H2O2). Peroxisomal diseases result from the dysfunction of one or more peroxisomal metabolic functions, the majority of which manifest as neurological abnormalities. The quantitation of peroxisomal metabolic functions (e.g. levels of specific metabolites and/or enzyme activity) has become the basis of clinical diagnosis of diseases associated with the organelle. The study of peroxisomal diseases has also contributed towards the further elucidation of a number of metabolic functions of peroxisomes.

Measurement of peroxisomal fatty acid beta-oxidation in cultured human skin fibroblasts

One of the main functions of mammalian peroxisomes is the beta-oxidation of a variety of fatty acids and fatty acid derivatives, including very long-chain fatty acids. Oxidation of these fatty acids is deficient in a number of different peroxisomal disorders, including the disorders of peroxisome biogenesis (Zellweger syndrome, neonatal adrenoleukodystrophy and infantile Refsum disease), X-linked adrenoleukodystrophy and a number of other disorders of peroxisomal beta-oxidation of known and unknown aetiology. Accurate measurement of peroxisomal fatty acid oxidation is of utmost importance for correct postnatal and prenatal diagnosis of these disorders. In this paper we describe a straightforward and accurate assay method to measure the beta-oxidation of palmitic acid (C16:0), hexacosanoic acid (C26:0) and pristanic acid in intact fibroblasts.

Intraorganellar localization of CoASH-independent phytanic acid oxidation in human liver peroxisomes

In human tissues phytanic acid is alpha-oxidized to pristanic acid in peroxisomes. Studies of the intraorganellar site of alpha-oxidation of [1-14C]phytanic acid to pristanic acid in peroxisomes isolated from human liver demonstrate that phytanoyl-CoA ligase is present in the peroxisomal membrane and that the enzyme system for alpha-oxidation of phytanic acid to pristanic acid is in the peroxisomal matrix. In contrast to the beta-oxidation system for fatty acids, the substrate for alpha-oxidation is free phytanic acid. The studies described in this manuscript report a novel fatty acid oxidation system where the substrate for the enzyme system is free fatty acid; however, phytanoyl-CoA ligase regulates the alpha-oxidation of phytanic acid at the organellar (peroxisomal) level.

Alterations of peroxisomal function in ischemia-reperfusion injury of rat kidney

We have previously demonstrated that ischemic injury results in the loss of peroxisomal functions (e.g., inhibition of catalase activity and fatty-acid beta-oxidation activity). To understand the molecular mechanism leading to the loss of peroxisomal beta-oxidation in ischemic tissue, we examined the levels of individual enzyme activities and proteins of the peroxisomal beta-oxidation system and overall fatty-acid oxidation in peroxisomes isolated from kidney exposed to ischemia-reperfusion injury. The peroxisomal beta-oxidation decreased with an increase in time of ischemic injury (53% and 43% of the control in kidneys exposed to 60 and 90 min ischemia, respectively). In vivo inactivation of catalase with aminotriazole and exposure of isolated peroxisomes to H2O2 resulted in inhibition of peroxisomal beta-oxidation system suggesting that this enzyme system is labile to excessive H2O2 produced during ischemic injury. The enzyme activities of lignoceroyl-CoA ligase, acyl-CoA oxidase, bifunctional enzymes and acyl-CoA thiolase (individual peroxisomal beta-oxidation enzymes) after 90 min of ischemia were 87, 80, 87 and 85% of the control, respectively. This decrease in enzyme activities was more pronounced following reperfusion (28, 11, 23 and 35% of the control, respectively). Immunoblot analysis of these enzymes indicated that the major loss of these enzyme activities during ischemia was due to their inactivation, whereas during reperfusion, proteolysis also contributed toward the observed loss of these activities. In summary, these results demonstrated that loss of peroxisomal beta-oxidation in ischemia-reperfusion injury was due to inactivation and proteolysis of beta-oxidation enzymes. Acyl-CoA oxidase was more sensitive to ischemia-reperfusion injury compared to other enzymes, and the overall loss of peroxisomal beta-oxidation may be a reflection of the loss of acyl-CoA oxidase activity, a rate-limiting enzyme.

Purification of peroxisomes and subcellular distribution of enzyme activities for activation and oxidation of very-long-chain fatty acids in rat brain

Brain contains high amounts of very-long-chain (VLC) fatty acids (> C22). Since mitochondria from liver and skin fibroblasts lack lignoceroyl-CoA ligase, in liver and skin fibroblasts fatty acids are exclusively oxidized in peroxisomes. Findings by Poulos and associates [9] suggested that contrary to liver and cultured skin fibroblasts brain mitochondria contain lignoceroyl-CoA ligase and can oxidize lignoceric acid. The present study was undertaken to develop a procedure for the isolation of subcellular organelles of higher purity from brain and to get a better understanding of the subcellular localization of the oxidation of VLC fatty acids in brain. The enzyme activities for activation and oxidation of palmitic and lignoceric acids were determined in peroxisomes, mitochondria, microsomes and a myelin fraction from rat brain and peroxisomes, mitochondria and microsomes purified from rat liver. Like in liver, brain lignoceroyl-CoA ligase activity in microsomes and peroxisomes was approx. 9 times higher than in mitochondria. In addition to palmitoyl-CoA ligase the antibodies against palmitoyl-CoA ligase inhibited the residual mitochondrial lignoceroyl-CoA ligase activity, meaning that lignoceroyl-CoA ligase activity in mitochondria was derived from palmitoyl-CoA ligase. Accordingly, in peroxisomes lignoceric acid was oxidized at 7 times higher rate than in mitochondria. Mitochondria were able to oxidize lignoceric acid efficiently when supplemented with lignoceroyl-CoA ligase activity from microsomes or myelin. These results show that in brain lignoceric acid is oxidized in peroxisomes and that lignoceroyl-CoA ligase activity is localized in peroxisomes and microsomes, but not in mitochondria. Peroxisomes and microsomes contain both lignoceroyl-CoA and palmitoyl-CoA ligases. Similar to peroxisomes and microsomes, the antibodies against palmitoyl-CoA ligase inhibited only the palmitoyl-CoA ligase activity in myelin but not the lignoceroyl-CoA ligase activity. These results suggest that in addition to palmitoyl-CoA ligase, myelin also contains lignoceroyl-CoA ligase.

Studies on the effect of fenoprofen on the activation and oxidation of long chain and very long chain fatty acids in hepatocytes and subcellular fractions from rat liver

We studied the effect of fenoprofen on the activation of palmitic acid (C16:0), lignoceric acid (C24:0) and cerotic acid (C26:0) in microsomal and peroxisomal fractions from rat liver. Fenoprofen was found to inhibit the formation of palmitoyl-CoA in both microsomal and peroxisomal fractions whereas the formation of lignoceroyl-CoA and cerotoyl-CoA was not inhibited at all. In freshly isolated rat hepatocytes palmitic acid beta-oxidation was progressively inhibited at increasing concentrations of fenoprofen, most probably due to its inhibitory effect on palmitoyl-CoA synthetase activity. On the other hand, fenoprofen was also found to inhibit the beta-oxidation of lignoceric acid and cerotic acid in rat hepatocytes. It is shown that the acyl-CoA oxidase activity with lignoceroyl-CoA as substrate was inhibited by fenoprofen whereas the palmitoyl-CoA and pristanoyl-CoA oxidase activities were not inhibited by fenoprofen. This finding provides an explanation for the inhibitory effect of fenoprofen on lignocerate and cerotate beta-oxidation in hepatocytes.

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.

Identification of phytanoyl-CoA ligase as a distinct acyl-CoA ligase in peroxisomes from cultured human skin fibroblasts

Phytanic acid accumulates in excessive amounts in Refsum disease, a rare neurological disorder, due to a defect in its alpha-oxidation enzyme system in peroxisomes. The activation of phytanic acid to phytanoyl-CoA by phytanoyl-CoA ligase is a prerequisite for its alpha-oxidation. The studies described in this manuscript report that phytanoyl-CoA ligase in peroxisomes is an enzyme distinct from the previously reported acyl-CoA ligases.

Effects of cyclodextrins on the hydrolysis of ganglioside GM1 by acid beta-galactosidases

The hydrolysis of ganglioside GM1 by acid beta-galactosidases was greatly enhanced by the inclusion of heptakis(2,6-di-O-methyl)-beta-cyclodextrin or alpha-cyclodextrin in the assay mixture. The other cyclodextrins tested were not effective. The extent of stimulation by these cyclodextrins was relatively smaller than those by taurodeoxycholate and taurochenodeoxycholate. However, it is suggested that stimulation by bile salts may be partly a reflection of the detergent effects of bile salts on GM1 and partly a reflection of the interaction between bile salts and the enzyme itself. On the other hand, the stimulation by the cyclodextrins seems to correlate to the formation of an inclusion complex between GM1 and cyclodextrin without enzyme protein interaction.

Topography of very-long-chain-fatty-acid-activating activity in peroxisomes from rat liver

We have investigated the localization of palmitoyl-CoA (hexadecanoyl-CoA) synthetase (EC 6.2.1.3) and cerotoyl-CoA (hexacosanoyl-CoA) synthetase in peroxisomes isolated from rat liver. Palmitoyl-CoA and cerotoyl-CoA synthetases, like acyl-CoA: dihydroxyacetone phosphate acyltransferase (EC 2.3.1.42), are present in the peroxisomal membrane. Trypsin treatment of intact peroxisomes led to the disappearance of both palmitoyl-CoA and cerotoyl-CoA synthetase activities but had little, if any, effect on L-alpha-hydroxy-acid oxidase (EC 1.1.3.15), D-amino acid oxidase (EC 1.4.3.3) or acyl-CoA:dihydroxyacetone phosphate acyltransferase. The latter three enzymes were inactivated if the trypsin treatment was preceeded by disruption of the peroxisomes by sonication. These results show that the active site, or at least domains essential for the activity of cerotoyl-CoA synthetase, like that of palmitoyl-CoA synthetase, is located on the cytosolic face of the peroxisomal membrane.

Rhizomelic chondrodysplasia punctata: biochemical studies of peroxisomes isolated from cultured skin fibroblasts

Peroxisomes isolated from cultured skin fibroblasts of two patients with rhizomelic chondrodysplasia punctata (RCDP) and two controls were compared for biochemical studies. These experiments provided the following results: (1) peroxisomes isolated from RCDP-cultured skin fibroblasts had the same density (1.175 g/ml) as control peroxisomes; (2) dihydroxyacetone phosphate acyltransferase activity, the first enzyme in the synthesis of plasmalogens, was deficient (0.5% of control) in RCDP peroxisomes and this activity was not observed in any other region of the gradient; (3) the rate of activation (lignoceroyl-CoA ligase) and oxidation of lignoceric acid was normal in RCDP peroxisomes; and (4) peroxisomes from RCDP contained 3-ketoacyl-CoA thiolase in the unprocessed form (44-kDa protein), whereas control peroxisomes had both processed (41-kDa protein) and unprocessed forms of 3-ketoacyl-CoA thiolase. The presence of both processed and unprocessed 3-ketoacyl-CoA thiolase in control peroxisomes and the unprocessed form in RCDP peroxisomes suggests that processing of 3-ketoacyl-CoA thiolase takes place in peroxisomes. Although the specific activity and percentage of activity of 3-ketoacyl-CoA thiolase in RCDP peroxisomes was only 22-26% of control, the normal oxidation of lignoceric acid in RCDP peroxisomes indicates that unprocessed 3-ketoacyl-CoA thiolase is active. The remaining peroxisomal 3-ketoacyl-CoA thiolase activity in RCDP was observed in a protein fraction (peroxisome ghosts) lighter than peroxisomes. The normal oxidation of fatty acids in peroxisomes and the absence of such activity in peroxisome ghosts (d = 1.12 g/ml) containing peroxisomal proteins in RCDP suggest that RCDP has only one population of functional peroxisomes (d = 1.175 g/ml).

Long-chain-acyl-CoA synthetase and very-long-chain-acyl-CoA synthetase activities in peroxisomes and microsomes from rat liver. An enzymological study

We have investigated the palmitic acid (C16:0) and cerotic acid (C26:0) activating activities in rat-liver microsomes and peroxisomes. The activation of the two fatty acids showed similar dependencies on ATP and coenzyme A, reflected in about equal apparent Km values both in microsomes and peroxisomes. In microsomes and peroxisomes similar apparent Km values for palmitic acid were found (15 microM and 22.8 microM, respectively), whereas apparent Km values for cerotic acid were 8.4 microM and 1.0 microM in microsomes and peroxisomes, respectively. The activation of cerotic acid was found to be inhibited to a progressively greater extent by increasing concentrations of 1-pyrenedecanoic acid (P10) as compared to the activation of palmitic acid, both in microsomes and peroxisomes. The inhibition by P10 of palmitic acid activation and cerotic acid activation was non-competitive in both organelles. From the observation that P10 activation is not affected by palmitic acid and cerotic acid, we conclude that P10 is activated by a distinct enzyme. Furthermore, our results are in accordance with earlier suggestions that activation of cerotic acid is brought about by an enzyme distinct from the palmitoyl-CoA synthetase.

Effect of ciprofibrate on the activation and oxidation of very long chain fatty acids

The effect of ciprofibrate, a hypolipidemic drug, was examined in the metabolism of palmitic (C16:0) and lignoceric (C24:0) acids in rat liver. Ciprofibrate is a peroxisomal proliferating drug which increases the number of peroxisomes. The palmitoyl-CoA ligase activity in peroxisomes, mitochondria and microsomes from ciprofibrate treated liver was 3.2, 1.9 and 1.5-fold higher respectively and the activity for oxidation of palmitic acid in peroxisomes and mitochondria was 8.5 and 2.3-fold higher respectively. Similarly, ciprofibrate had a higher effect on the metabolism of lignoceric acid. Treatment with ciprofibrate increased lignoceroyl-CoA ligase activity in peroxisomes, mitochondria and microsomes by 5.3, 3.3 and 2.3-fold respectively and that of oxidation of lignoceric acid was increased in peroxisomes and mitochondria by 13.4 and 2.3-fold respectively. The peroxisomal rates of oxidation of palmitic acid (8.5-fold) and lignoceric acid (13.4-fold) were increased to a different degree by ciprofibrate treatment. This differential effect of ciprofibrate suggests that different enzymes may be responsible for the oxidation of fatty acids of different chain length, at least at one or more step(s) of the peroxisomal fatty acid beta-oxidation pathway.

Effect of clofibrate on peroxisomal lignoceroyl-CoA ligase activity

The effect of a 2-week clofibrate (0.5%)-fortified diet on peroxisomal palmitoyl-CoA and lignoceroyl-CoA ligases was studied. The activities of palmitoyl-CoA and lignoceroyl-CoA ligases in peroxisomes isolated from clofibrate-treated animals were 4.4- and 4.0-fold higher than those of the controls. The different degrees of increases in these two enzyme activities support the previous conclusions that in peroxisomes palmitoyl-CoA ligase and lignoceroyl-CoA ligase are different enzymes. Since clofibrate treatment increases both of these peroxisomal acyl-CoA ligase activities and normal palmitoyl-CoA ligase is the source of the partial activity for the oxidation of lignoceric acid in X-ALD, treatment with a hypolipidemic drug, which can increase human peroxisomal enzyme activities, may be helpful in lowering the amount of the pathogen, VLC fatty acids, in X-ALD.

Adrenoleukodystrophy: impaired oxidation of fatty acids due to peroxisomal lignoceroyl-CoA ligase deficiency

Very long chain fatty acids (lignoceric acid) are oxidized in peroxisomes and pathognomonic amounts of these fatty acids accumulate in X-adrenoleukodystrophy (X-ALD) due to a defect in their oxidation. However, in cellular homogenates from X-ALD cells, lignoceric acid is oxidized at a rate of 38% of control cells. Therefore, to identify the source of this residual activity we raised antibody to palmitoyl-CoA ligase and examined its effect on the activation and oxidation of palmitic and lignoceric acids in isolated peroxisomes from control and X-ALD fibroblasts. The normalization of peroxisomal lignoceric acid oxidation in the presence of exogenously added acyl-CoA ligases and along with the complete inhibition of activation and oxidation of palmitic and lignoceric acids in peroxisomes from X-ALD by antibody to palmitoyl-CoA ligase provides direct evidence that lignoceroyl-CoA ligase is deficient in X-ALD and demonstrates that the residual activity for the oxidation of lignoceric acid was derived from the activation of lignoceric acid by peroxisomal palmitoyl-CoA ligase. This antibody inhibited the activation and oxidation of palmitic acid but had little effect on these activities for lignoceric acid in peroxisomes from control cells. Furthermore, these data provide evidence that peroxisomal palmitoyl-CoA and lignoceroyl-CoA ligases are two different enzymes.

Acyl-CoA ligases from rat brain microsomes: an immunochemical study

Acyl-CoA ligase activities, solubilized from rat brain microsomes, were fractionated into three different peaks by hydroxyapatite chromatography. Based on physical and chemical properties, we suggested that peak A (pamitoyl-CoA ligase) and peak C (lignoceroyl-CoA ligase) were two different enzymes (A. Bhushan, R. P. Singh, and I. Singh (1986) Arch. Biochem. Biophys. 246, 374-380). We raised antibodies against purified liver microsomal palmitoyl-CoA ligase (EC 6.2.1.3) and examined the effect of this antibody on acyl-CoA ligase activities for palmitic, arachidonic and lignoceric acids in microsomal enzyme extract and different acyl-CoA ligase peaks from the hydroxyapatite column. In an enzyme activity assay system in microsomal extract, the antisera inhibited the palmitoyl-CoA ligase activity but had very little effect on the acyl-CoA ligase activities for arachidonic and lignoceric acids. This antisera inhibited the acyl-CoA ligase activities for these three fatty acids in peak A and had no effect on these activities in peak B or peak C. Western blot analysis demonstrated that antibody to liver microsomal palmitoyl-CoA ligase cross-reacted with only peak A (palmitoyl-CoA ligase), but not with peak B or peak C. This immunochemical study demonstrates that palmitoyl-CoA ligase does not share immunological determinants with acyl-CoA ligases in peaks B or C, thus demonstrating that palmitoyl-CoA ligase (peak A) is different from the arachidonoyl-CoA and lignoceroyl-CoA ligase activities in peaks B or C.

Distinct long chain and very long chain fatty acyl CoA synthetases in rat liver peroxisomes and microsomes

Mitochondria, peroxisomes, and microsomes were isolated from rat liver homogenates, and stearic acid and lignoceric acid beta-oxidation, as well as stearoyl CoA synthetase and lignoceroyl CoA synthetase activities in the three organelles, were compared. Stearic acid beta-oxidation in peroxisomes was sixfold greater compared to the oxidation in mitochondria. Lignoceric acid beta-oxidation, observed only in peroxisomes, was fivefold lower compared to stearic acid beta-oxidation. Stearoyl CoA synthetase was present whereas lignoceroyl CoA synthetase was absent in mitochondria. Stearoyl CoA synthetase and lignoceroyl CoA synthetase activities were present in microsomes and peroxisomes, but the activity of stearoyl CoA synthetase was several-fold greater compared to lignoceroyl CoA synthetase in both organelles. The differing responses to detergents and phospholipids of stearoyl CoA and lignoceroyl CoA synthetase activities in microsomes as well as peroxisomes indicated that each activity was catalyzed by a separate enzyme. Differences in detergent and phospholipid response were also noted when either stearoyl CoA or lignoceroyl CoA synthetase activity in one organelle was compared with the corresponding activity in the other organelle, suggesting that the same activity in different organelles may be catalyzed by separate enzyme proteins.

Peroxisomal lignoceroyl-CoA ligase deficiency in childhood adrenoleukodystrophy and adrenomyeloneuropathy

We previously reported that in childhood adrenoleukodystrophy (C-ALD) and adrenomyeloneuropathy (AMN), the peroxisomal beta-oxidation system for very long chain (greater than C22) fatty acids is defective. To further define the defect in these two forms of X chromosome-linked ALD, we examined the oxidation of [1-14C]lignoceric acid (n-tetracosanoic acid, C24:0) and [1-14C]lignoceroyl-CoA (substrates for the first and second steps of beta-oxidation, respectively). The oxidation rates of lignoceric acid in C-ALD and AMN were 43% and 36% of control values, respectively, whereas the oxidation rate of lignoceroyl-CoA was 109% (C-ALD) and 106% (AMN) of control values, respectively. On the other hand, the oxidation rates of palmitic acid (n-hexadecanoic acid) and palmitoyl-CoA in C-ALD and AMN were similar to the control values. These results suggest that lignoceroyl-CoA ligase activity may be impaired in C-ALD and AMN. To identify the specific enzymatic deficiency and its subcellular localization in C-ALD and AMN, we established a modified procedure for the subcellular fractionation of cultured skin fibroblasts. Determination of acyl-CoA ligase activities provided direct evidence that lignoceroyl-CoA ligase is deficient in peroxisomes while it is normal in mitochondrial and microsomes. Moreover, the normal oxidation of lignoceroyl-CoA as compared with the deficient oxidation of lignoceric acid in isolated peroxisomes also supports the conclusion that peroxisomal lignoceroyl-CoA ligase is impaired in both C-ALD and AMN. Palmitoyl-Coa ligase activity was found to be normal in peroxisomes as well as in mitochondria and microsomes. This normal peroxisomal palmitoyl-CoA ligase activity as compared with the deficient activity of lignoceroyl-CoA ligase in C-ALD and AMN suggests the presence of two separate acyl-CoA ligases for palmitic and lignoceric acids in peroxisomes. These data clearly demonstrate that the pathognomonic accumulation of very long chain fatty acids in C-ALD and AMN is due to a deficiency of peroxisomal very long chain (lignoceric acid) acyl-CoA ligase.

Fatty acid metabolism in renal ischemia

The increase in free fatty acids in the ischemic tissue is a consistent observation and these free fatty acids are considered to play a role in the cellular toxicity. To elucidate the cause of higher levels of free fatty acids in ischemic tissue, we examined the catabolism of fatty acids. The beta-oxidation of lignoceric (24:0), palmitic (16:0) and octanoic (8:0) acids and the peroxidation of fatty acids were measured at different times of renal ischemia in whole kidney homogenate. The enzymatic activities for the oxidation of fatty acids decreased with the increase in ischemia time. However, the lipid peroxide levels increased 2.5-fold of control with ischemic injury. Sixty min of ischemia reduced the rate of oxidation of octanoic, palmitic and lignoceric acids by 57, 59 and 69%, respectively. Almost similar loss of fatty acid oxidation activity was observed in the peroxisomes and mitochondria. These data suggest that loss of mitochondrial and peroxisomal fatty acid beta-oxidation enzyme activities from ischemic injury may be one of the factors responsible for the higher levels of free fatty acids.

Stereoselectivity in the 2-methylbutyrate incorporation into anteiso fatty acids in Bacillus subtilis mutants

Two Bacillus subtilis mutants defective in branched-chain alpha-ketoacid dehydrogenase can grow when 2-methylbutyrate is provided in trypticase soy medium. Both enantiomers of the acid supported growth of the mutants but the (S)-(+)-isomer (natural) was more active than the (R)-(-)-isomer (unnatural). The mutants utilized these isomers as primer to specifically synthesize either enantiomer of anteiso fatty acids. No racemization of the isomer primers was observed during the synthesis. Thus, cells grown with (-)-isomer possessed anteiso fatty acids (over 80%) of the total fatty acids, being entirely the unnatural enantiomer. The stereospecific synthesis was found to be controlled at the step of 2-methylbutyryl-CoA synthesis. In a wild strain, only (+)-specific acyl-CoA synthetase was detected. In the mutants, either enantiomer of 2-methylbutyrate could simultaneously induce both types, (+)-specific and (-)-specific, of acyl-CoA synthetase. (+)-Specific synthetase had a higher activity and affinity towards substrate than (-)-specific synthetase. The detailed preparative procedures for (R)-(-)- and 2-[3,4-3H]methylbutyric acid are described.

Very long chain fatty acid beta-oxidation by subcellular fractions of normal and Zellweger syndrome skin fibroblasts

Very long chain fatty acid (VLCFA) beta-oxidation was compared in homogenates and subcellular fractions of cultured skin fibroblasts from normal individuals and from Zellweger patients who show greatly reduced numbers of peroxisomes in their tissues. beta-Oxidation of lignoceric (C24:0) acid was greatly reduced compared to controls in the homogenates and the subcellular fractions of Zellweger fibroblasts. The specific activity of C24:0 acid beta-oxidation was highest in the crude peroxisomal pellets of control fibroblasts. Fractionation of the crude mitochondrial and the crude peroxisomal pellets on Percoll density gradients revealed that the C24:0 acid oxidation was carried out entirely by peroxisomes, and the peroxisomal beta-oxidation activity was missing in Zellweger fibroblasts. In contrast to the beta-oxidation of C24:0 acid, the beta-oxidation of C24:0 CoA was observed in both mitochondria and peroxisomes. We postulate that a very long chain fatty acyl CoA (VLCFA CoA) synthetase, which is different from long chain fatty acyl CoA synthetase, is required for the effective conversion of C24:0 acid to C24:0 CoA. The VLCFA CoA synthetase appears to be absent from the mitochondrial membrane but present in the peroxisomal membrane.

Purification and characterization of palmitoyl-CoA ligase from rat brain microsomes

We have previously shown the existence of two separate enzymes for the synthesis of palmitoyl-CoA and lignoceroyl-CoA in rat brain microsomal membranes (1). Palmitoyl-CoA ligase activity was solubilized from brain microsomal membranes with 0.3% Triton X-100 and purified 93-fold by a combination of protein purification techniques. The Km values for the substrates palmitic acid, CoASH and ATP were 11.7 microM, 5.88 microM and 3.77 mM respectively. During activation of palmitic acid ATP is hydrolyzed to AMP and pyrophosphate, as evidenced by the inhibition of this activation by 5 mM concentrations of AMP, pyrophosphate or AMP and pyrophosphate to 70%, 60% and 85% respectively. The divalent metal ion Mg2+ was required for activity; its replacement with Mn2+ resulted in a 35% decrease in activity. Palmitoyl-CoA ligase activity was inhibited by the addition of oleic or stearic acids whereas addition of lignoceric acid or behenic acid had no effect. This supports our previous observation that palmitoyl-CoA and lignoceroyl-CoA are synthesized by two different enzymes in rat brain microsomal membranes.

Characterization of rat brain microsomal acyl-coenzyme A ligases: different enzymes for the synthesis of palmitoyl-coenzyme A and lignoceroyl-coenzyme A

Palmitic acid solubilized with Triton WR-1339 was converted to palmitoyl-CoA by microsomal membranes but lignoceric acid solubilized with Triton WR-1339 was not an effective substrate even though the detergent dispersed the same amount of these fatty acids and was also not inhibitory to the enzyme [I. Singh, R. P. Singh, A. Bhushan, and A. K. Singh (1985) Arch. Biochem. Biophys. 236, 418-426]. This observation suggested that palmitoyl-CoA and lignoceroyl-CoA may be synthesized by two different enzymes. We have solubilized the acyl-CoA ligase activities for palmitic and lignoceric acid of rat brain microsomal membranes with Triton X-100 and resolved them into three separate peaks (fractions) by hydroxylapatite chromatography. Fraction A (palmitoyl-CoA ligase) had high specific activity for palmitic acid and Fraction C (lignoceroyl-CoA ligase) for lignoceric acid. Specific activity of palmitoyl-CoA ligase for palmitic acid was six times higher than in Fraction C and specific activity of lignoceroyl-CoA ligase for lignoceric acid was four times higher than in Fraction A. At higher concentrations of Triton X-100 (0.5%), lignoceroyl-CoA ligase loses activity whereas palmitoyl-CoA ligase does not. Lignoceroyl-CoA ligase lost 60% of activity at 0.6% Triton X-100. Palmitoyl-CoA ligase (T1/2 of 4.5 min) is more stable at 40 degrees C than lignoceroyl-CoA ligase (T1/2 of 1.5 min). The pH optimum of palmitoyl-CoA ligase was 7.7 and that of lignoceroyl-CoA ligase was 8.4. Similar to our results with intact membranes, palmitic acid solubilized with Triton WR-1339 was converted to palmitoyl-CoA by palmitoyl-CoA ligase whereas lignoceric acid when solubilized with Triton WR-1339 was not able to act as substrate for lignoceroyl-CoA ligase. Since solubilized enzyme activities for synthesis of palmitoyl-CoA and lignoceroyl-CoA from microsomal membranes can be resolved into different fractions by column chromatography and demonstrate different properties, we suggest that in microsomal membranes palmitoyl-CoA and lignoceroyl-CoA are synthesized by two different enzymes.

Lignoceroyl-CoASH ligase: enzyme defect in fatty acid beta-oxidation system in X-linked childhood adrenoleukodystrophy

We have previously reported that the peroxisomal beta-oxidation system for very long chain fatty acids is defective in X-linked childhood adrenoleukodystrophy [(1984) Proc. Natl. Acad. Sci. USA 81, 4203-4207]. In order to elucidate the specific enzyme defect, we examined the oxidation of [1-14C]lignoceric acid, [1-14C]lignoceroyl-CoA and (1-14C)-labelled alpha,beta-unsaturated lignoceroyl-CoA (substrates for the 1st, 2nd, and 3rd steps of the beta-oxidation cycle, respectively). These studies suggest that the pathognomonic accumulation of very long chain fatty acids in X-linked childhood ALD may be due to the defective activity of peroxisomal very long chain (lignoceroyl-CoA) acyl-CoA ligase.

Peroxisomal oxidation of lignoceric acid in rat brain

The oxidation of [1-14C]lignoceric acid was studied in different subcellular fractions of rat brain. The highest specific activity for oxidation of [1-14C]lignoceric acid to acetate was observed in the light mitochondrial fraction. The oxidation of [1-14C]lignoceric acid had an absolute requirement for CoASH and ATP. It was stimulated by NAD and FAD by 400 and 280 percent, respectively, whereas addition of carnitine and KCN had no effect. These properties suggest that in brain [1-14C]lignoceric acid is oxidized in peroxisomes.