A convenient and versatile method for the purification of CoA thiol esters

Studies of the mode of action of erucic acid on heart metabolism

The effects of erucic acid on the oxidative metabolism of rat-heart mitochondria have been investigated using intact animals, perfused beating heart, isolated mitochondria and mitochondrial extracts. Feeding rats with a diet containing erucic acid was found to lead to a diminished ability of the isolated heart mitochondria to oxidize various substrates, in accordance with previous reports (Houtsmuller et al., Biochim. Biophys. Acta 218 (1970) 564). This effect was almost pronounced with palmitylcarnitine as substrate, in which case the rate of oxidation was decreased by more than 50% at such a low erucic acid content in the diet as 1.4% given over 2-4 weeks. Oxidation of palmitylcarnitine was also found to be inhibited when erucylcarnitine was added to isolated heart mitochondria from control animals, in agreement with earlier observations (Christophersen and Bremer, FEBS Lett. 23 (1972) 230; Biochim. Biophys. Acta 280 (1972) 506). The inhibition was accompanied by a decrease in the rate and extent of reduction of mitochondrial flavoprotein. Experiments with perfused beating rat-heart likewise revealed an inhibition of flavoprotein reduction, as well as nicotinamide nucleotide reduction, when erucate was added to the perfusing medium of the beating heart respiring with oleate--but not with octanoate--as substrate. These data together with those earlier published in the literature indicate that erucic acid may interfere with the enzyme system involved in the mitochondrial oxidation of long-chain fatty acids, probably at the level of acyl-CoA dehydrogenase. Kinetic data supporting this conclusion, obtained with extracts of rat-heart mitochondria containing the acyl-CoA dehydrogenase and electron-transferring flavoprotein system, are presented. The possible implications of these results for the known effect of dietary erucic acid in causing an accumulation of fat in the heart are discussed.

Studies on phytanoyl-CoA 2-hydroxylase and synthesis of phytanoyl-coenzyme A

Phytanoyl-CoA 2-hydroxylase (PAHX), an iron(II) and 2-oxoglutarate-dependent oxygenase, catalyses an essential step in the mammalian metabolism of beta-methylated fatty acids. Phytanoyl-CoA was synthesised and used to develop in vitro assays for PAHX. The product of the reaction was confirmed as 2-hydroxyphytanoyl-CoA by NMR and mass spectrometric analyses. In accord with in vivo analyses, hydroxylation of both 3R and 3S epimers of the substrate was catalysed by PAHX. Both pro- and mature- forms of PAHX were fully active.

Synthesis and intramitochondrial levels of valproyl-coenzyme A metabolites

A number of valproate adverse reactions are due to its interference with several metabolic pathways, including that of fatty acid oxidation. In order to resolve which mitochondrial enzymes of fatty acid oxidation are inhibited by which VPA intermediates we have developed methods to synthesize their CoA ester forms. This paper describes the synthesis of VPA acyl-CoA ester metabolites as well as data on the fate of VPA in rat liver mitochondria. Valproyl-CoA, Delta2-valproyl-CoA, and 3-OH-valproyl-CoA were obtained through chemical synthesis. 3-Keto-valproyl-CoA was prepared by a novel enzymatic procedure followed by a combination of solid-phase extraction and preparative HPLC purification. This approach proved to be efficient in obtaining all the beta-oxidation intermediates of valproyl-CoA. The synthetic standards were used for the determination of intramitochondrial concentrations of valproyl-CoA, Delta2-valproyl-CoA, 3-OH-valproyl-CoA, and 3-keto-valproyl-CoA by HPLC. These levels were determined after incubation of intact rat liver mitochondria with VPA under conditions of state 3 and state 4 respiration. The results show that valproyl-CoA and to a much lesser extent 3-keto-valproyl-CoA are the main metabolites of VPA in mitochondria. This information will be of great use in resolving the mechanisms involved in the inhibition of mitochondrial processes like fatty acid oxidation by VPA.

Biosynthesis of the peptide bond in the coenzyme N-(7-mercaptoheptanoyl)-L-threonine phosphate

The biochemical mechanism for the formation of the amide bond in N-(7-mercaptoheptanoyl)-L-threonine phosphate (HS-HTP) has been studied by measuring the incorporation of L-[3-(3)H]threonine into N-(7-mercaptoheptanoyl)-L-threonine (HS-HT) by cell extracts (CE) of Methanosarcina thermophila incubated with different precursors. Synthesis of HS-HT was observed from L-[3-(3)H]threonine and 7-mercaptoheptanoic acid (HS-H) when the incubations were conducted with either crude CE or Sephadex column-purified CE. In the presence of CE, the synthesis of HS-HT was found to be inhibited 66% by preincubation of the extract with ATPase, indicating that ATP was involved in the biosynthesis. In spite of this indication of ATP involvement in the coupling reaction, incubation of the crude CE with L-[3-(3)H]threonine, HS-H, and ATP was found to inhibit the formation of HS-HT. In contrast, the synthesis of HS-HT in the presence of Sephadex column-purified CE was found to be stimulated by the addition of ATP. Incubation of the crude CE with the CoA thioester of 7-mercaptoheptanoic acid (HS-HCoA) or the mixed disulfide formed between coenzyme M and 7-mercaptoheptanoic acid did not stimulate the biosynthesis. The biosynthesis of HS-HT was found to be strongly inhibited by an ethanol extract of the crude CE. This inhibition was found to be attributed to the HS-HTP present in the extract. Stimulation of HS-HT biosynthesis 300-fold was observed when the Sephadex column-purified CE was incubated with L-[3-(3)H]threonine and 7-mercaptoheptanoyl phosphate (HS-H-P). Data indicate that HS-HT is produced by the phosphorylation of HS-H to HS-H-P with ATP, which then reacts with L-threonine to produce HS-HT.

Synthesis of sn-1,2-diacylglycerols by monoacylglycerol acyltransferase from Manduca sexta fat body

The pathway for the synthesis of sn-1,2-diacylglycerol stimulated by the action of adipokinetic hormone (AKH) in the insect fat body is unknown. Previous results from this laboratory suggested that the hydrolysis of stored triacylglycerol to sn-2-monoacylglycerol followed by the stereospecific acylation of sn-2-monoacylglycerol catalyzed by a monoacylglycerol-acyltransferase (MGAT) could be the major route of AKH-stimulated sn-1,2-diacylglycerol synthesis. Thus, MGAT might represent a key enzyme of this pathway. In this study we characterized the MGAT activity from the Manduca sexta fat body. The activity, which was assayed by acylation of 2-monoolein using radioactive labeled palmitoyl-CoA, was found to be primarily a microsomal enzyme. The products of the acylation of 2-monoolein were 1,2-diacylglycerol (40-50%), 1,3-diacylglycerol (20-30%), and triacylglycerol (30-40%). The presence of triacylglycerol as a product revealed the presence of diacylglycerol-acyltransferase activity in the fat body microsomes. The pH optimum of MGAT activity was 7.0, and the dependence of the activity on the concentration of 2-monoolein showed saturation kinetics. An endogenous MGAT activity, which represented 20% of the maximal activity observed with added substrate, was detected. Optimal concentrations of palmitoyl-CoA ranged between 0.10-0.20 mM. The specific activity of MGAT, measured under optimal conditions, was about 0.6 nmol DG formed/min-mg protein. MGAT activity was greatest with 2-monoolein, and lower activity was observed when a saturated 2-monoacylglycerol was employed. The activity observed with sn-1-monoacylglycerol was lower than that observed with sn-2-monoacylglycerol. AKH did not stimulate MGAT activity, suggesting that either the enzyme is not under hormonal regulation or the monoacylglycerol pathway is not involved in the AKH-stimulated production of sn-1,2-diacylglycerol in the M. sexta fat body.

Beta-oxidation of unsaturated fatty acids in humans. Isoforms of delta 3, delta 2-enoyl-CoA isomerase

This investigation was undertaken in order to elucidate the human enzymes which participate in metabolism of the double bonds of unsaturated fatty acids during beta-oxidation. The results indicate that the human monofunctional delta 3, delta 2-enoyl-CoA isomerase (EC 5.3.3.8) with the native M(r) of 70,000 differed significantly from its rat counterpart [Palosaari et al. (1990) J. Biol. Chem. 265, 3347-3353]; the isoelectric point of the human isoform was over three pH-units more acidic, it showed different chromatographic behaviour, the human enzyme did not show any clear-cut substrate chain-length specificity and only a weak immunological cross-reactivity was detected with the antibody to rat liver mitochondrial short-chain enzyme. This explains the failure of attempts to apply the rat data directly to human beings. Another isomerase activity from human liver was found to be a part of the isomerase-hydratase-dehydrogenase polypeptide showing immunological cross-reactivity with the previously characterized peroxisomal multifunctional enzyme (MFE) from rat liver.

Peroxisomes and beta-oxidation of long-chain unsaturated carboxylic acids

Degradation of unsaturated long-chain carboxylic acids by beta-oxidation, which is a compartmentalized process occurring in both mitochondria and peroxisomes in mammalian cells, was studied using rat liver as a model tissue. Inclusion of (poly)unsaturated fatty acids in the perfusion medium resulted in an increased concentration of catalase-H2O2 complex indicating on-going peroxisomal beta-oxidation. For this to occur, an active peroxisomal delta 3, delta 2-enoyl-CoA isomerase was required for metabolism of the double bonds at odd-numbered positions in acyl-CoA. Experiments with isolated subcellular organelles from rat liver confirmed the presence of isomerase in the peroxisomes, and the enzyme was subsequently isolated with apparent homogeneity. Comparison of amino acid sequences from the enzyme with a published sequence for a bifunctional protein from rat liver identified them representing the same molecule. The peroxisomal bifunctional protein can thus act as a multifunctional hydratase-dehydrogenase-isomerase enzyme. Examination of the mitochondrial isomerase revealed that rat liver mitochondria possess two isoenzymes: a long-chain isomerase not induced by clofibrate-treatment and showing a preference for C10-C12 substrates, and a clofibrate-inducible short-chain isomerase which gave the highest catalytic activity with C6 substrates. Experiments with isolated peroxisomes and unsaturated acyl-CoAs demonstrated that the beta-oxidation of fatty acids having double bonds at even-numbered positions was dependent on 2,4-dienoyl-CoA reductase in peroxisomes, as in mitochondria. Immunocytochemical experiments using the protein A-gold labelling technique, and comparison of their physicochemical properties indicated that all the mammalian reductases purified so far are mitochondrial isoenzymes. It turned out during the isolation of 3-hydroxyacyl-CoA epimerase that there was no monofunctional epimerase at all in the rat liver. Instead, the epimerization reaction occurred via dehydration-hydration catalyzed by two distinct stereospecific hydratases, 2-enoyl-CoA hydratase 1 (the classic hydratase) and 2-enoyl-CoA hydratase 2 (a novel hydratase). The present data demonstrate that peroxisomes contain all the enzymes required for the beta-oxidation of unsaturated fatty acids and support the notion that one of the physiological functions of peroxisomal beta-oxidation is to metabolize long-chain hydrophobic carboxylic acids to shorter, more polar metabolites which are then either metabolized further in the body or excreted.

Occurrence of a long-chain delta 3,delta 2-enoyl-CoA isomerase in rat liver

Isoproteins of delta 3,delta 2-enoyl-CoA isomerase (EC 5.3.3.8), an auxiliary enzyme in the beta-oxidation of unsaturated fatty acids having double bonds at odd-numbered positions, were studied in livers of control and clofibrate-treated rats. When liver extracts were applied to a hydroxyapatite column at pH 7.0, the previously characterized peroxisomal trifunctional hydratase-dehydrogenase-isomerase enzyme and the mitochondrial isomerase, which shows a preference for short-chain substrates, were eluted almost in parallel. In addition to these activities, a separate isomerase was observed to elute at a lower potassium phosphate concentration in the gradient. Experiments with extracts of purified mitochondria and peroxisomes demonstrated the mitochondrial origin of this third activity. Studies on the kinetic properties of the third isomerase showed that it has a preference for C10-C12 substrates. An Mr of 200,000 was obtained for the native protein by gel-filtration chromatography. Antibodies to mitochondrial short-chain isomerase and peroxisomal trifunctional enzyme did not recognize this novel mitochondrial isoenzyme. The immunological non-cross-reactivity can be interpreted as suggesting that the different isomerases are not closely related at the level of the primary structure of the polypeptide chain. The present data demonstrate that, similar to many other enzymes of beta-oxidation, delta 3,delta 2-enoyl-CoA isomerase has at least three isoenzymes in rat liver: mitochondrial short- and long-chain isomerases and an additional peroxisomal isoenzyme, which in this case is a part of a multifunctional protein.

Reductive biotransformations of organic compounds by cells or enzymes of yeast

Saccharomyces cerevisiae catalyses the asymmetric reductive biotransformation of a variety of compounds containing a carbonyl group or carbon-carbon double bond. Oxidoreductases participating in these reactions which have commercial potential in biotransformation processes are likely to have relatively broad substrate specificity. Important carbonyl reductases falling into this category include YADH- and yeast NADP-dependent beta-ketoester reductases. The enoyl reductase component of the FAS complex may have a role in asymmetric yeast reduction of carbon-carbon double bonds of unnatural substrates. Other nicotinamide-requiring oxidoreductases of yeast are also surveyed to rationalize observed biotransformations of whole yeast cells in terms of specific enzymes. Genetic and protein engineering may enable enzymes to be tailored to accept new substrates. A greater understanding of the enzymes and reactions involved will facilitate further optimization and exploitation of these catalytic systems in industrial processes.

Comparison of the binding affinities of acyl-CoA-binding protein and fatty-acid-binding protein for long-chain acyl-CoA esters

Bovine and rat liver acyl-CoA-binding proteins (ACBP) were found to exhibit a much higher affinity for long-chain acyl-CoA esters than both bovine hepatic and cardiac fatty-acid-binding proteins (hFABP and cFABP respectively). In the Lipidex 1000- as well as the liposome-binding assay, bovine and rat hepatic ACBP effectively bound long-chain acyl-CoA ester, h- and c-FABP were, under identical conditions, unable to bind significant amounts of long-chain acyl-CoA esters. When FABP, ACBP and [1-14C]hexadecanoyl-CoA were mixed, hexadecanoyl-CoA could be shown to be bound to ACBP only. The experimental results give strong evidence that ACBP, and not FABP, is the predominant carrier of acyl-CoA in liver.

A simple enzymatic method for the preparation of radiolabeled erucoyl-CoA and other long-chain fatty acyl-CoAs and their characterization by mass spectrometry

A simple two-step method for the biosynthesis of radiolabeled erucoyl-coenzyme A of high specific activity and other long-chain fatty acyl-coenzyme A (acyl-CoA) thioesters is reported. 1-14C-labeled erucic and oleic acids, as well as unlabeled ricinoleic and nervonic acids, were incubated at 35 degrees C with coenzyme A in the presence of ATP, MgCl2, and acyl-CoA synthetase (EC 6.2.1.3) from Pseudomonas spp. to yield the corresponding CoA thioesters. Following incubation, each thioester was purified by rapid passage through a disposable reverse-phase C18 extraction column. The overall yields were greater than 90% and the purities greater than 95%, based on the distribution of radioactivity, and chromatographic and spectral properties. Fast ion bombardment-mass spectrometry was employed to confirm the structures of the various acyl-CoAs.

Measurement of the acyl-CoA intermediates of beta-oxidation by h.p.l.c. with on-line radiochemical and photodiode-array detection. Application to the study of [U-14C]hexadecanoate oxidation by intact rat liver mitochondria

The quantitative isolation of acyl-CoA esters of chain length C2-C17 from mitochondrial incubations and their analysis by reverse-phase radio-h.p.l.c. is described. Photodiode-array detection was used to characterize 2-enoyl-CoA esters. The chromatographic behaviour of all 27 intermediates of the beta-oxidation of hexadecanoyl-CoA is documented. Only C16, C14 and C12 intermediates were detected in uncoupled mitochondria oxidizing [U-14C]hexadecanoyl-CoA in the presence of fluorocitrate and carnitine, providing evidence for some organization of the enzymes of beta-oxidation [Garland, Shepherd & Yates (1965) Biochem. J. 97, 587-594; Sumegi & Srere (1984) J. Biol. Chem. 259, 8748-8752]. Rotenone increased concentrations of 3-hydroxyacyl-CoA and 2-enoyl-CoA esters and inhibited flux. These experiments provide the first direct unambiguous measurements of acyl-CoA esters in intact respiring rat liver mitochondrial fractions.

Beta-oxidation of polyunsaturated fatty acids in peroxisomes. Subcellular distribution of delta 3,delta 2-enoyl-CoA isomerase activity in rat liver

The metabolism of the double bonds at the delta 3 position in fatty acids was studied in rat liver. Infusion of delta 3-trans-dodecenoic acid into isolated perfused liver and subcellular fractionation studies showed the presence of both peroxisomal and mitochondrial delta 3,delta 2-enoyl-CoA isomerase activity (EC 5.3.3.8). These findings together with the previous demonstration of peroxisomal 2,4-dienoyl-CoA reductase (EC 1.3.1.34) [(1981) J. Biol. Chem. 256, 8259-8262] and D-3-OH-acyl-CoA epimerase (EC 5.1.2.3) [(1985) FEBS Lett. 185, 129-134] activities show that peroxisomes possess all the auxiliary enzymes required for the beta-oxidation of unsaturated fatty acids.

Synthesis of coenzyme A ester of retinoic acid: intermediate in vitamin A metabolism

Coenzyme A esters of all-trans- and 13-cis-retinoic acid were synthesized for use in studying vitamin A metabolism. The esters were obtained by two different synthetic methods starting from retinoic acids, which were converted to activated succinimidyl esters or anhydrides. These in turn were coupled with coenzyme A to form their respective thioesters. The retinoyl coenzyme A esters were purified by reverse-phase high performance liquid chromatography.

A study of the metabolism of [U-14C]3-methyl-2-oxopentanoate by rat liver mitochondria using h.p.l.c. with continuous on-line monitoring of radioactive intact acyl-coenzyme A intermediates

A reverse-phase h.p.l.c. system for the resolution of the acyl-CoA intermediates of the degradation of 3-methyl-2-oxopentanoate is described. The validation of a method for the measurement of radioactive intermediates produced by the incubation of [U-14C]3-methyl-2-oxopentanoate with rat liver mitochondrial fractions is described. The absence of bicarbonate caused the accumulation of [14C]propionyl-CoA. The accumulation of [14C]2-methylbutyryl-CoA was observed in incubations with mitochondrial fractions derived from riboflavin-deficient animals. Studies of the accumulation of labelled intermediates with time suggest that there is regulation of the pathway of isoleucine degradation at methylmalonyl-CoA mutase, as suggested for valine [Corkey, Martin-Requero, Walajtys-Rode, Williams & Williamson (1982) J. Biol. Chem. 257, 9668-9676]. These studies demonstrate that h.p.l.c. with on-line continuous radiochemical detection is a powerful method for the investigation of the control of intermediary metabolism.

beta-Hydroxy acyl-CoA inhibition of mitochondrial ATP production

beta-Hydroxypalmitoyl-CoA and beta-hydroxystearoyl-CoA were synthesized, purified and quantitated. beta-Hydroxypalmitoyl-CoA and beta-hydroxystearoyl-CoA instantly and reversibly inhibited oxidative phosphorylation by rabbit heart mitochondria oxidizing pyruvate. [8-14C]ADP uptake studies showed that the beta-hydroxy acyl-CoA species linearly inhibited the adenine nucleotide translocase system. Free beta-hydroxy fatty acids at comparable concentrations (0.005 mM) did not affect ADP uptake or state III respiration.

Purification and characterization of 2-enoyl-CoA reductase from bovine liver

Mitochondrial 2-enoyl-CoA reductase from bovine liver was purified and characterized. A simple three-step purification was developed, involving ion-exchange chromatography to separate the bulk of the NADPH-dependent 2,4-dienoyl-CoA reductase, followed by chromatography on Blue Sepharose and adenosine 2',5'-bisphosphate-Sepharose. Homogeneous enzyme with a subunit Mr of 35 500 is obtained in 35% yield. The Mr of the native enzyme, determined by three different methods, yielded values that suggest that the enzyme is dimeric. NADPH is required as cofactor, and cannot be replaced by NADH. The activity of the purified enzyme towards 2-trans-double bonds in 2-monoene and 2,4-diene structures was investigated. 2-Enoyl-CoA reductase reduced the double bonds in a series of 2-trans-monoenoyl-CoA esters with different chain lengths, but did not exhibit significant activity towards 2-trans-double bonds of 2,4-dienoyl-CoA esters. This result is discussed in the light of analogous observations with enoyl-CoA hydratase.

Assay of long-chain acyl-CoAs in a complex reaction mixture

A method has been developed which allows the quantitative analysis of labeled or unlabeled acyl-CoAs in complex reaction mixtures. The method is based on (a) a quantitative solubilization of acyl-CoAs and lipids, directly in the reaction vessel, by 0.05 M Tris-HCl, pH 7.5/CHCl3/CH3OH (1/3/3, v/v/v); (b) monodimensional TLC of aliquots of the whole reaction mixture, resolving malonyl-CoA, acetyl-CoA, long-chain acyl-CoAs, polar lipids and neutral lipids plus free fatty acids; and (c) quantitation by TLC densitometry and/or TLC radiochromatography. All fractions--and particularly long chain-acyl-CoAs--can then be analyzed for distribution and label of fatty acyl moieties.

Purification and characterization of maize leaf acetyl-coenzyme A carboxylase

Maize leaf acetyl-CoA carboxylase was purified from whole tissue homogenates by precipitation with polyethylene glycol and ammonium sulfate, and gel filtration. Recoveries were approximately 5% with 100-fold increases in specific activity. The molecular weight of the native enzyme is estimated at 500,000 from the elution volume of a calibrated Ultrogel AcA 22 column. Electrophoresis in polyacrylamide gel containing 1% sodium dodecyl sulfate revealed a single subunit of Mr 60,000-61,000. Investigation of the kinetic properties of the purified enzyme indicates that Mg X ATP is the active substrate, with free ATP inhibiting and Mg2+ activating the enzyme. Km's for acetyl-CoA and HCO3- are about 0.1 and 2 mM, respectively. ADP inhibition is competitive with respect to ATP, but uncompetitive with respect to acetyl-CoA. The observed responses of purified acetyl-CoA carboxylase to changes in pH, and in concentrations of Mg2+, ATP, and ADP, and the reported changes in the chloroplastic concentrations of these effectors during light-dark transitions of chloroplasts are consistent with increased acetyl-CoA carboxylase activity upon illumination of chloroplasts.

Preparation of bromo[1-14C]acetyl-coenzyme A as an affinity label for acetyl-coenzyme A binding sites

Bromo[1-14C]acetyl-CoA has been prepared from CoASH and the N-hydroxysuccinimide ester of bromo[1-14C]acetic acid, and unlabeled bromoacetyl-CoA by reaction of CoASH with bromoacetyl bromide. The products were purified by high-pressure liquid chromatography. Purified bromoacetyl-CoA was characterized, and found to be a potent alkylating agent with a substantial stability in aqueous solution: it decomposed at 30 degrees C and pH 6.6 and 8.0 with halftimes of 3.3 and 2.5 h, respectively. The major breakdown products were CoASH and CoAS X CO X CH2 X SCoA. Bromo[1-14C]acetyl-CoA has been used to affinity label the acetyl-CoA binding site of 3-hydroxy-3-methylglutaryl-CoA synthase from ox liver. It was found to irreversibly inhibit the enzyme activity and bind covalently with a stoichiometry for complete inhibition of about 0.8 mol/mol enzyme dimer.

Purification by affinity chromatography of 2,4-dienoyl-CoA reductases from bovine liver and Escherichia coli

1. Dye-ligand chromatography using immobilized Cibacron blue F3GA (blue Sepharose CL-6B) and Procion red HE3B (Matrex gel red A) as matrices and general ligand chromatography employing immobilized 2',5'-ADP (2',5'-ADP-Sepharose 4B) and immobilized 3',5'-ADP (3',5'-ADP-Agarose) were employed for purification of NADPH-dependent 2-enoyl-CoA reductase and 2,4-dienoyl-CoA reductase from bovine liver (formerly called 4-enoyl-CoA reductase [Kunau, W. H. and Dommes, P. (1978) Eur. J. Biochem. 91, 533-544], as well as 2,4-dienoyl-CoA reductase from Escherichia coli. 2. The NADPH-dependent 2-enoyl-CoA reductase from bovine liver mitochondria was separated from 2,4-dienoyl-CoA reductase by dye-ligand chromatography (Matrex gel red A/KCl gradient) as well as by general ligand affinity chromatography (2',5'-ADP-Sepharose 4B/NADP gradient). The enzyme was obtained in a highly purified form. 3. The NADPH-dependent 2,4-dienoyl-CoA reductase from bovine liver mitochondria was purified to homogeneity using blue Sepharose CL-6B, Matrex gel red A, and 2',5'-ADP-Sepharose 4B chromatography. 4. The bacterial 2,4-dienoyl-CoA reductase was completely purified by ion-exchange chromatography on DEAE-cellulose followed by a single affinity chromatography step employing 2',5'-ADP-Sepharose 4B and biospecific elution from the column with a substrate, trans,trans-2,4-decadienoyl-CoA. 5. The application of dye-ligand and general ligand affinity chromatography for purification of NADPH-dependent 2,4-dienoyl-CoA reductases taking part in the beta-oxidation of unsaturated fatty acids is discussed. It is concluded that making use of coenzyme specificity for binding and substrate specificity for elution is essential for obtaining homogeneous enzyme preparations.

Metabolism of pent-4-enoate in rat heart. Reduction of the double bond

1. Soluble extracts from rat heart and liver mitochondria were used to evaluate the early steps in the conversion of pent-4-enoyl-CoA into tricarboxylic acid-cycle intermediates. Hitherto the unresolved problem was the reduction of the double bond of pent-4-enoate. 2. Soluble extracts from heart mitochondria reduced pent-4-enoyl-CoA and penta-2,4-dienoyl-CoA in the presence of NADPH at rates (nmol/min per mg of protein) of 0.9 +/- 0.1 and 132 +/- 8 and from the liver mitochondria at the rates of 1.9 +/- 0.2 and 52 +/- 6 respectively. No reduction of acryloyl-CoA was found. 3. We show that primarily the double bond in position 4, not in position 2, of penta-2,4-dienoyl-CoA is reduced. 4. It is concluded that the principal metabolic pathway of penta-4-enoate is reduction of the double bond in position 4 after an initial oxidation of penta-2,4-dienoyl-CoA. The pent-2-enoyl-CoA thus formed can be further metabolized by the usual enzymes of beta-oxidation, and by the further metabolism of propionyl-CoA to tricarboxylic acid-cycle intermediates.

A bifunctional enzyme from glyoxysomes. Purification of a protein possessing enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase activities

1. Enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase copurified when extracts from cotyledons of 5-day-old cucumber seedlings were fractionated by acetone precipitation, ion-exchange chromatography on CM-cellulose and affinity chromatography on blue-dextran-Sepharose. The protein was purified 600-fold with 16% recovery. 2. Bifunctionality of the protein was substantiated by exactly coinciding activity profiles upon chromatography on hydroxyapatite, CM-cellulose, or blue-dextran-Sepharose respectively. Analysis of the purified protein using isoelectric focusing as well as native electrophoresis confirmed the presence of a bifunctional protein. A monospecific antiserum could be raised against the homogeneous protein. 3. Further characterization of the protein revealed that the two enzyme activities are contained in a single peptide chain of Mr 75000. An extremely alkaline isoelectric point of pH 9.8 was determined. 4. The bifunctional protein was localized in glyoxysomes which were shown to be the exclusive site of beta-oxidation at this stage of germination. At least 10% of the enzyme were attributable to the organelle's membrane.

The acylation of lysophosphatidylcholine by subcellular fractions of guinea-pig cerebral cortex

The acylation of lysophosphatidylcholine by isolated subcellular fractions of guinea-pig cerebral cortex has been determined. The microsomal fraction contained the highest acylation activity, in terms of both specific and total activity. In all particulate fractions, including synaptic plasma membrane and mitochondria, there was a high correlation (correlation coefficient r = 0.90; P less than 0.001) between acylation and the activity of the microsomal enzyme, NADPH-cytochrome c reductase. No correlation existed between acylation and the activities of (Na+ + K+)-ATPase, acetylcholinesterase or succinate dehydrogenase. Acyl-CoA synthetase and lysophosphatidylcholine/acyltransferase, the individual enzymes responsible for acylation were enriched in the microsomal fraction. The activities of both enzymes in subcellular fractions correlated well with those of NADPH-cytochrome c reductase, with the exception that acyl-CoA synthetase activity in the mitochondrial fraction was largely independent of endoplasmic reticulum. Neither synaptic plasma membranes nor mitochondria appeared to possess significant amounts of acyltransferase activity. The results indicate that the acylation of lysophosphatidylcholine is confined to the endoplasmic reticulum, and that activity present in the synaptic plasma membrane or mitochondrial fraction is attributable to microsomal contamination.

Transacylation as a chain-termination mechanism in fatty acid synthesis by mammalian fatty acid synthetase. Synthesis of butyrate and hexanoate by lactating cow mammary gland fatty acid synthetase

1. Purified cow mammary gland fatty acid synthetase synthesized long-chain unesterified and short-chain esterified fatty acids. 2. A direct relationship was observed between the amount of short-chain products synthesized and the concentration of acetyl-CoA in the incubation medium. 3. The short-chain products were identified as butyryl-CoA and hexanoyl-CoA. 4. Inhibition of the terminating thioester hydrolase of the fatty acid synthetase complex with phenylmethanesulphonyl fluoride did not inhibit the synthesis of short-chain products. 5. It is suggested that the synthesis of short-chain fatty acids involves the reverse of the 'loading' reaction.

Isomerization of the double bonds of a conjugated fatty acid during beta-oxidation

The beta-oxidation of an unsaturated fatty acid containing conjugated double bonds at odd-numbered carbon atoms has not previously been studied. It is, therefore, not clear whether, during the beta-oxidation of such an acid, the double bonds will be isomerized by enoyl-CoA isomerase (delta 3 - delta 2-enoyl-CoA isomerase) with the loss or retention of its conjugated nature. To investigate the problem, (E,E)-3,5-octadienoyl-CoA was synthesized for use as a model substrate, and enoyl-CoA isomerase was partially purified from bovine liver. The isomerization was followed by spectrophotometric and gas liquid chromatographic methods, and the results suggested that the isomerization of the model substrate proceeded with retention of a conjugated double bond system. It is, therefore, proposed that the beta-oxidation intermediate of alpha-eleostearic acid (delta 9,11,13 fatty acid) will also isomerize with retention of the conjugated double bond system.