Long Chain Fatty Acid Activation in Subcellular Preparations from Rat Liver

5-Aminoimidazole-4-carboxyamide-ribonucleoside (AICAR)-stimulated hepatic expression of Cyp4a10, Cyp4a14, Cyp4a31, and other peroxisome proliferator-activated receptor α-responsive mouse genes is AICAR 5'-monophosphate-dependent and AMP-activated protein kinase-independent

5-Aminoimidazole-4-carboxyamide-ribonucleoside (AICAR), a prodrug activator of AMP-activated protein kinase (AMPK), increased hepatic expression of cytochrome P450 4a10, 4a14, and 4a31 mRNAs 2-, 3-, and 4-fold, respectively, and liver microsomal lauric acid ω-hydroxylation increased 2.8-fold. Likewise, mRNA levels of the peroxisome proliferator-activated receptor α (PPARα)-responsive genes, Acox1, Acadm, Cpt1a, and Fabp1, were also increased by AICAR treatment. AICAR did not elicit these changes in PPARα null mice. In isolated murine hepatocytes, AICAR and adenosine produced similar effects, and these responses were blocked by the PPARα antagonist [(2S)-2-[[(1Z)-1-methyl-3-oxo-3-[4-(trifluoromethyl)phenyl]-1-propenyl]amino]-3-[4-[2-(5-methyl-2-phenyl-4-oxazolyl)ethoxy]phenyl]propyl]-carbamic acid ethyl ester (GW6471). Inhibition of AMPK using compound C (dorsomorphin or 6-[4-(2-piperidin-1-ylethoxy)phenyl]-3-pyridin-4-ylpyrazolo[1,5-a]pyrimidine) did not block the induction of the PPARα-responsive genes by AICAR or adenosine, and 6,7-dihydro-4-hydroxy-3-(2'-hydroxy[1,1'-biphenyl]-4-yl)-6-oxo-thieno[2,3-b]pyridine-5-carbonitrile (A-769662), a non-nucleoside, direct activator of AMPK, did not increase expression of PPARα-responsive genes. An inhibitor of adenosine kinase, 5-iodotubercidin, blocked these responses, suggesting that the phosphorylation of AICAR and adenosine to AICAR 5'-monophosphate (ZMP) or AMP, respectively, was required. Concentrations of ZMP and AMP were elevated and ATP levels diminished at 24 h. The PPARα-dependent responses were associated with increased concentrations of oleic acid, a potent PPARα agonist, and diminished levels of oleoyl-CoA. Oleoyl-CoA synthase activity was inhibited by ZMP and AMP with IC(50) values of 0.28 and 0.41 mM, respectively. These results suggest that PPARα is activated by increased concentrations of free fatty acids that may arise from impaired fatty acid metabolism caused by altered levels of ATP, AMP, and ZMP after AICAR or adenosine treatment.

Effects of a novel dual lipid synthesis inhibitor and its potential utility in treating dyslipidemia and metabolic syndrome

We have identified a novel omega-hydroxy-alkanedicarboxylic acid, ESP 55016, that favorably alters serum lipid variables in obese female Zucker (fa/fa) rats. ESP 55016 reduced serum non-HDL-cholesterol (non-HDL-C), triglyceride, and nonesterified fatty acid levels while increasing serum HDL-C and beta-hydroxybutyrate levels in a dose-dependent manner. ESP 55016 reduced fasting serum insulin and glucose levels while also suppressing weight gain. In primary rat hepatocytes, ESP 55016 increased the oxidation of [(14)C]palmitate in a dose- and carnitine palmitoyl transferase-I (CPT-I)-dependent manner. Furthermore, in primary rat hepatocytes and in vivo, ESP 55016 inhibited fatty acid and sterol synthesis. The "dual inhibitor" activity of ESP 55016 was unlikely attributable to the activation of the AMP-activated protein kinase (AMPK) pathway because AMPK and acetyl-CoA carboxylase (ACC) phosphorylation states as well as ACC activity were not altered by ESP 55016. Further studies indicated the conversion of ESP 55016 to a CoA derivative in vivo. ESP 55016-CoA markedly inhibited the activity of partially purified ACC. The activity of partially purified HMG-CoA reductase was not altered by the xenobiotic-CoA. These data suggest that ESP 55016-CoA favorably alters lipid metabolism in a model of diabetic dyslipidemia in part by initially inhibiting fatty acid and sterol synthesis plus enhancing the oxidation of fatty acids through the ACC/malonyl-CoA/CPT-I regulatory axis.

Palmitoyl-CoA synthetase on the external surface of isolated rat hepatocytes

After incubating isolated rat hepatocytes with [1-14 C]palmitic acid, CoA and ATP (+MgCl2), a significant amount of [1-14 C]palmitoyl-CoA was found in the incubation medium. There was no correlation between its rate of synthesis and the degree of intactness of the cells. The results indicate that there is a long-chain fatty acyl-CoA synthetase active on the external surface of the hepatocyte plasma membrane. The activity of this enzyme was negligible in primary cultures of rat hepatocytes, suggesting that the exofacial long-chain acyl-CoA synthetase is an artifact of the collagenase perfusion technique used to prepare the hepatocytes.

Two distinct long-chain-acyl-CoA synthetases in guinea pig Harderian gland

Two distinct long-chain-acyl-CoA synthetases which have different kinetic properties were identified in the guinea pig Harderian gland. One was localized in the microsomes and the other in the mitochondria. The relative V(max) values of the microsomal enzyme were 8.1, 1.7 and 1 and the apparent Km values were 66.7, 12.0 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values of the mitochondrial enzyme were 2.7, 3.5 and 1 and the apparent Km values were 33.3, 29.9 and 30.0 microM for palmitic, linoleic and arachidonic acids, respectively. The relative V(max) values for the liver microsomal enzyme were 2.0, 2.5 and 1, while those of the liver mitochondrial enzyme were 4.1, 3.9 and 1 with palmitic, linoleic and arachidonic acids, respectively. There were no difference between the microsomal and the mitochondrial enzymes in the liver, regarding apparent Km values; these were 38.4, 29.9 and 22.0 microM for palmitic, linoleic and arachidonic acids, respectively. Thus, the substrate specificity and catalytic rate of the mitochondrial enzyme in Harderian gland for palmitic, linoleic and arachidonic acids were similar to the liver enzyme, but not to the microsomal enzyme in Harderian gland. On the other hand, the antiserum raised against the rat liver enzyme immune-titrated and immuno-blotted the enzymes from Harderian gland microsomes and liver, but not so the enzyme from Harderian gland mitochondria. Thus, the microsomal enzyme in Harderian gland had a common immunogenic epitope(s) with the liver enzyme, but the mitochondrial enzyme did not. The Harderian gland mitochondrial enzyme was a distinct protein from liver enzymes. The catalytic and immunogenic characteristics suggest that the enzyme proteins in the Harderian gland are unique, that is, different from that in the liver. The large V(max) value of the Harderian gland microsomal enzyme for palmitic acid suggests that it contributes to the synthesis of a large amount of the secretory lipid and the high Km value to maintenance of cellular lipid in this organ. The evidence that long-chain-acyl-CoA synthetase in the mitochondria is distinct from that in the microsomes was first found in guinea pig Harderian gland.

Acyl-CoA synthetase activity depends on the phospholipid composition of rat liver plasma membranes

The dependence of acyl-CoA synthetase on the lipid composition of rat liver plasma membranes has been investigated. For this purpose the composition of the membranes was modified by incorporation of different phospholipids in the presence of partially purified lipid transfer proteins. Another approach to the modification of the membrane phospholipid composition was treatment with exogenous phospholipase C and subsequent enrichment with different phospholipids. The experiments performed in vitro indicated that the presence of certain phospholipids such as phosphatidylnositol, phosphatidylethanolamine, phosphatidylglycerol and phosphatidylserine was essential for the activation of long chain fatty acids by acyl-CoA synthetase. However, some differences were observed when oleate and palmitate were used as substrates. Sphingomyelin was found to inhibit this activity especially when oleic acid served as substrate. In addition, we tried to modify in vivo the membrane lipid composition by treatment with D-galactosamine, which is known to induce acute hepatitis and cause biochemical and biophysical alterations in liver membranes. The results thus obtained confirmed the idea that the augmentation of the membrane lipids and especially of PI, PE and PG was accompanied by acyl-CoA synthetase activation. The presence of two different enzymes, activating the saturated and unsaturated fatty acids is discussed.

Interaction of fatty acids, acyl-CoA derivatives and retinoids with microsomal membranes: effect of cytosolic proteins

This paper reviews characteristics of microsomal membrane structure; long chain fatty acids, acyl CoA derivatives, retinoids and the microsomal formation of acyl CoA derivatives and retinyl esters. It is analyzed how the movement of these molecules at the intracellular level is affected by their respective binding proteins (Fatty acid binding protein, acyl CoA binding protein and cellular retinol binding protein). Studies with model systems using these hydrophobic ligands and the lipid-binding or transfer proteins are also described. This topic is of interest especially because in the esterification of retinol the three substrates and the three binding proteins may interact.

Metabolic stereoisomeric inversion of ibuprofen in mammals

Studies on the mechanism and enzymology of metabolic ibuprofen isomerization constituted the focus of this investigation. Comparative in vivo studies revealed that this biotransformation proceeded via a proton abstraction mechanism in all tested species of mammals, which is in agreement with the previous reports. Direct evidence supporting this conclusion stemmed from the in vitro epimerization of ibuprofen-CoA thioester in rat liver homogenates. Chemically synthesized (R)-ibuprofen-CoA thioester was rapidly transformed to its (S)-counterpart by subcellular hepatic preparations. Examination of this epimerase activity in various rat tissue homogenates indicated that this enzyme was highly tissue specific. This biochemical reaction mainly took place in the liver and kidney, whereas low levels of enzyme activity were associated with other tissues. Nevertheless, the liver and kidney homogenates failed to invert (R)-ibuprofen directly even in the presence of all the necessary cofactors. Presumably, the failure to characterize this bioconversion was due to the lack of enzymatic acyl-CoA synthesis in these homogenates. It is noteworthy that the '2-arylpropionyl-CoA epimerase' catalyzed the transformation from either direction and with high turnover rates. The catalytic efficiency of (S)-ibuprofen CoA epimerization appeared to be greater than that of the (R)-counterpart. These in vitro findings suggest that the step of acyl-CoA formation assume a pivotal role in controlling the stereoselectivity and efficiency of the in vivo metabolism. As the responsible acyl-CoA synthetase(s) in different species of animals may exert the reaction with different degrees of enantiomeric preference and efficiency, the resulting stereochemical outcome and metabolic rates of this bioinversion vary accordingly. Consequently, in guinea pigs, this biotransformation proceeds in both directions with nearly equal efficiency, whereas it is virtually unidirectional and slow in humans. Currently, the purification and characterization of this novel '2-arylpropionyl-CoA epimerase' from rat livers constitute the focus of this investigation.

Tissue phospholipid fatty acid composition in genetically lean (Fa/-) or obese (fa/fa) Zucker female rats on the same diet

The fatty acid composition of serum total lipids, of phospholipids of various organs (liver, heart, kidney), and of nervous structures (brain, retina, sciatic nerve, myelin, synaptosomes) have been compared in lean (Fa/-) and genetically obese (fa/fa) Zucker female rats. Both received a standard commercial diet including 37% of 18:2n-6 and 5% of n-3 polyunsaturated fatty acids (PUFA), 1.7% of which were in the form of 20:5n-3 and 22:6n-3. In comparison with lean rats, the results for the obese rats pointed out (i) no difference in the fatty acid composition of nervous structures; (ii) a decrease of 18:2n-6 (from -8% to -35%) and of 20:4n-6 (from -9% to -49%) in serum, liver and in kidney; this was compensated for by an increase in 20:3n-6 (from +30% to +320%) and in total n-3 PUFA (from +68% to +76%); (iii) a decrease of 20:4n-6 (-18%) and of 22:6n-3 (-24%) in heart compensated for by an increase in 18:2n-6 (+39%) and in 20:3n-6 (+233%); and (iv) constant levels of total PUFA (n-6 and n-3) in the various fractions studied, except in serum where this level decreased (-23%). Finally, except for the nervous structures, tissue phospholipids of obese rats included a lower proportion of 20:4n-6 and a higher proportion of 20:3n-6. This resulted in a significant reduction in the 20:4n-6/20:3n-6 ratio; by contrast, the 20:3n-6/18:2n-6 ratio increased. The results suggest that in Zucker rats, the obese character (fa/fa) affects the desaturation-elongation process of 18:2n-6 to 20:4n-6 by specifically decreasing delta 5-desaturase activity.

Delta 6 and delta 5 desaturase activities in liver from obese Zucker rats at different ages

delta 6 Desaturation of linoleic acid (18:2 n-6) and delta 5 desaturation of dihomo-gamma-linolenic acid (20:3 n-6) were measured in liver microsomes from genetically obese Zucker rats (fa/fa) and from their lean littermates (Fa/--). Both groups were fed a balanced commercial diet. The rats were 6, 9 and 12 weeks old, which corresponded to stages in their active growth period. The content of total fatty acids and n-6 polyunsaturated fatty acids in whole liver and liver microsomes was also determined in order to ascertain how the desaturase activities measured in vitro reflected regulation of essential fatty acid metabolism in vivo. Contrary to values obtained for delta 6 desaturation, delta 5 desaturation at nonsaturating substrate levels were lower in obese rats than in lean controls. In contrast, at saturating substrate level, the maximal delta 5 desaturase activities were the same in both phenotypes and they increased with age. Study of delta 5 desaturation kinetics (1/V vs 1/S) showed that Vm did not differ between 12-week-old obese and lean rats, whereas KM in obese rats was much lower than in controls, expressing the very low affinity of the enzyme for the substrate in obese animals. The fatty acid composition of liver lipids reflected the results of desaturase activities in vitro. In particular, the ratios 20:4 n-6/20:3 n-6 were lower in obese rats than in lean rats, which can be explained by the lower conversion of 20:3 n-6 into 20:4 n-6 by delta 5 desaturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-chain fatty acyl-CoA synthetase of rat adrenal microsomes. Effect of ACTH and epinephrine

Acyl-CoA synthetase activity with various long-chain fatty acid substrates and its kinetic properties were measured in rat adrenal microsomes. The apparent Michaelis constants (Km) for substrate fatty acids increased in the order eicosa-8,11,14-trienoic acid less than alpha-linolenic acid less than linoleic acid less than palmitic acid. The maximum velocities with these fatty acids decreased in the order linolenic greater than eicosa-8,11,14-trienoic acid greater than palmitic acid. The synthesis of radioactivity palmitoyl-CoA, linoleyl-CoA, alpha-linolenyl-CoA and eicosa-8,11,14-trienoyl-CoA from the respective radioactive substrates decreased in the presence of all the other fatty acids mentioned above. These effects were inversely correlated with their apparent Km values. These results support the idea of a single long-chain fatty acyl-CoA synthetase in the adrenal microsomal fraction for the acid tested. After testing the influence of different hormones, it was shown that the administration of epinephrine, ACTH and dexamethasone caused a significant decrease in the activity of the long-chain fatty acid-CoA synthetase. This inhibition is independent of the one produced by the same hormones on the desaturation of linoleic to gamma-linolenic acid.

Acyl-CoA synthetase activity in Plasmodium knowlesi-infected erythrocytes displays peculiar substrate specificities

In its blood stages the malaria parasite, Plasmodium, displays very high lipid metabolism. We present evidence for an abundant long-chain acyl-CoA synthetase (EC 6.2.1.3) activity in Plasmodium knowlesi-infected simian erythrocytes. The activity was found to be 20-fold higher in the schizont-infected (the last parasite stage) than in control erythrocytes. The cosubstrate requirements of the enzyme were similar to those previously reported for acyl-CoA synthetases from other sources. Among the separated reaction products of oleyl-CoA synthetase, only PPi and oleyl-CoA were inhibitory, with Ki over 350 microM. The fatty acid specificity of the parasite acyl-CoA synthetase activity was fairly marked and depended on the unsaturation state of the substrate. The tested fatty acids displayed similar Vmax, whereas their Km ranged from 11 (palmitate) to 59 microM (arachidonate). Finally, experiments involving heat inactivation and separation on hydroxyapatite excluded the presence of a specific arachidonyl-CoA synthetase identical to those present in other cells. On the other hand, fatty acid competition experiments evidenced the existence of at least two distinct enzymatic sites for fatty acid activation in P. knowlesi-infected simian erythrocytes: one is specific for saturated fatty acids and the other for polyunsaturated species, whereas oleate could be activated at both sites.

Kinetics of human spermatozoa long-chain fatty acid: CoASH ligase

The kinetics of long-chain saturated fatty acid activation were studied in the supernatant obtained from Triton-treated human spermatozoa. Sperm long-chain fatty acid: CoASH ligase (AMP) (E.C. 6.2.1.3) was able to activate myristic, palmitic, and stearic acids, but was incapable of utilizing lauric, arachidic, and behenic acids. Peak activity was obtained with palmitic acid. Although the Kms for each fatty acid were similar (4.3 to 5.0 microM), the Vmax was several-fold higher for palmitate. In contrast, ligase from liver homogenates assayed under identical conditions activated lauric through stearic acids, with maximal rates being noted with myristic acid. When compared with nongerminal tissues, sperm ligase appears unique because of its narrower acyl substrate specificity.

Activation of palmitic acid by human spermatozoa

Human spermatozoa were studied to determine if a long chain fatty acid, CoASH ligase (AMP) (E.C. 6.2.1.3), was present. Ligase activity was measured with a radioligand millipore filter technique and was readily detectable in spermatozoa or in the protein fraction extracted with Triton X-100, but was not present in seminal plasma. The assay was optimized for pH, protein concentration, and incubation time. Activity was dependent upon palmitic acid, ATP, coenzyme A, and a divalent cation. Sperm ligase appeared similar to the ligase characterized from other tissues by sharing a common pH optimum (approximately 8.0-8.4), and a preference for magnesium over manganese in the incubation media.

Substrate specificity of fatty-acyl-CoA ligase in liver microsomes

The substrate specificity of fatty-acyl-CoA ligase in liver microsomes has been studied in a system in which fatty acids are present initially as complexes with unilamellar vesicles of phosphatidylcholine. The latter were prepared by cosonication of phospholipids and different fatty acids. As compared with previous studies of the enzyme the activity of acyl-CoA ligase is several-fold higher for assays carried out with fatty acid substrates added as components of a bilayer. This was true for all fatty acids studied. Also as compared with data reported previously in the literature there was a systematic relationship between the structure of fatty acids, activity at Vmax for synthesis of acyl-CoA and avidity of binding to the ligase. Activity at Vmax was greatest for lauric acid and decreased with increasing chain length. The apparent avidity of enzyme for fatty acids was greatest for octanoic acid and decreased as chain length increased.

Long-chain acyl-coenzyme A synthetase from rat brain microsomes. Kinetic studies using [1-14C]docosahexaenoic acid substrate

The activation of docosahexaenoic acid by rat brain microsomes was studied using an assay method based on the extraction of unreacted [1-14C]docosahexaenoic acid and the insolubility of [1-14C]docosahexaenoyl-CoA in heptane. This reaction showed a requirement for ATP, CoA, and MgCl2 and exhibited optimal activity at pH 8.0 in the presence of dithiothreitol and when incubated at 45 degrees C. The apparent Km values for ATP (185 microM), CoA (4.88 microM), MgCl2 (555 microM) and [1-14C]docosahexaenoic acid (26 microM) were determined. The presence of bovine serum albumin or Triton X-100 in the incubation medium caused a significant decrease in the Km and Vm values for [1-14C]docosahexaenoic acid. The enzyme was labile at 45 degrees C (t1/2:3.3 min) and 37 degrees C (t1/2:26.5 min) and lost 36% of its activity after freezing and thawing. The transition temperature (Tc) obtained from Arrhenius plot was 27 degrees C with the activation energies of 74 kJ/mol between 0 degrees C and 27 degrees C and 30 kJ/mol between 27 degrees C and 45 degrees C. [1-14C]Palmitic acid activation in rat brain and liver microsomes showed apparent Km values of 25 microM and 29 microM respectively, with V values of 13 and 46 nmol X min-1 X mg protein-1. The presence of Triton X-100 (0.05%) in the incubation medium enhanced the V value of the liver enzyme fourfold without affecting the Km value. Brain palmitoyl-CoA synthetase, on the other hand, showed a decreased Km value in the presence of Triton X-100 with unchanged V. The Tc obtained were 25 degrees C and 28 degrees C for brain and liver enzyme with an apparent activation energy of 109 and 24 kJ/mol below and above Tc for brain enzyme and 86 and 3.3 kJ/mol for liver enzyme. The similar results obtained for the activation of docosahexaenoate and palmitate in brain microsomes suggest the possible existence of a single long-chain acyl-CoA synthetase. The differences observed in the activation of palmitate between brain and liver microsomes may be due to organ differences. Fatty acid competition studies showed a greater inhibition of labeled docosahexaenoic and palmitic acid activation in the presence of unlabeled unsaturated fatty acids. The Ki values for unlabeled docosahexaenoate and arachidonate were 38 microM and 19 microM respectively for the activation of [1-14C]docosahexaenoate. In contrast, the competition of unlabeled saturated fatty acids for activation of labeled docosahexaenoate is much less than that for activation of labeled palmitate.(ABSTRACT TRUNCATED AT 400 WORDS)

Brominated vegetable oil myopathy: inhibition at multiple sites

Skeletal muscle lipid storage was induced by feeding rats brominated vegetable oil (BVO). The defect was examined by measuring radioactive substrate oxidation, intermediates of fatty acid oxidation, and activities of oxidative enzymes. One- and U-[14C] palmitate and 1-[14C] pyruvate oxidation were reduced in muscle after four doses of BVO. Inhibition of U-[14C] palmitate oxidation occurred after two doses. Short chain acylcoenzyme A(CoA) derivatives accumulated in the muscle. Several enzymes of beta-oxidation were significantly reduced, with the greatest reduction in 3-ketoacyl-CoA thiolase. The inhibition probably affected multiple sites of CoA and CoA-derivative metabolism.

Carnitine long-chain acyltransferase and oxidation of palmitate, palmitoyl coenzyme A and palmitoylcarnitine by pea mitochondria preparations

Palmitoylcarnitine was oxidised by pea mitochondria.L-carnitine was an essential addition for the oxidation of palmitate or palmitoylCoA. When palmitate was sole substrate, ATP and Mg(2+) were also essential additives for maximum oxidation. Additions of CoA inhibited the oxidation of palmitate. It was shown that CoA was acting as a competitive inhibitor of the carnitine-stimulated O2 uptake. It is suggested that palmitoylacarnitine and carnitine passed through the mitochondrial barrier with ease but palmitoylCoA and CoA did not. The presence of carnitine long-chain acyl (palmitoyl)transferase (EC 2.3.1.21) in pea-cotyledon mitochondria was shown. This enzyme may play a role in the transport of long-chain acyl groups through membrane barriers.

Computer simulation of metabolism in palmitate-perfused rat heart. I. Palmitate oxidation

A computer model of the fatty acid oxidation pathway in perfused rat heart was constructed. It includes uptake, activation, and beta-oxidation of fatty acids, triglyceride synthesis and hydrolysis, and carnitine-dependent transport of acyl groups across the mitochondrial membrane under pseudosteady state conditions. Fatty acid utilization may be limited by beta-oxidation in hypoxia or ischemia but probably not in aerobic conditions. Nonesterified fatty acids bound to proteins are found to be metabolically available. The model predicts that stearate, but not palmitate, can support the highest observed respiration rate for perfused rat heart without supplementation by other substrates. Fatty acids are preferentially oxidized rather than being stored as triglycerides because the cystosolic acyl CoA level is lower than the Km for triglyceride synthesis. It is suggested that feedback inhibition of triglyceride lipase regulates utilization of triglycerides as fuel in aerobic hearts.

Acid:coenzyme A ligase in brain: fatty acid specificity in cellular and subcellular fractions

We measured long-chain fatty acid: coenzyme A (CoA) ligase (EC 6.2.1.3) activity with four fatty acids in brain homogenates, and cellular and subcellular fractions to determine whether there are differences in activity that could be correlated with differences in fatty acid composition and metabolism. In rat brain homogenates, ligase activity varied appreciably with the four acids, with 18:2 greater than 18:1 greater than 16:0 greater than 22:1 (nmol acyl-CoA formed/min/mg protein: 1.46, 1.20, 0.96, and 0.57, respectively). This order was similar under all incubation conditions tested, including variable pH and fatty acid concentrations. The relative specific activities (RSA, 16:0 = 1.0) with the four substrates were similar in rat brain homogenate, mitochondria, and microsomes, with the highest specific activities in the latter fraction. The RSA were also similar in ox brain homogenates, in rabbit brain microsomes prepared from gray and white matter, in neurons isolated from rat brain, and in cultured neuroblastoma cells. Rat liver homogenates had a significantly different pattern of RSA. These results indicate that the ligase(s) has a preference for certain fatty acids, but suggest that the major control of fatty acid composition and metabolism is a function of subsequent metabolic steps.

Activation and transport of fatty acids in ovarian mitochondria: effect of Lh

Enzymes of fatty acid activation and transport were studied in luteinized rat ovaries. Luteal mitochondria were found to contain high levels of palmitoyl-CoA synthetase and carnitine palmitoyl-transferase activities. In addition, studies on the effect of palmitate concentration on palmitoyl-CoA synthetase activity revealed the possible existence of two forms of the enzyme: Km values of 0.34 mM and 21.33 mM, with Vmax of 3.64 and 66.67 nmoles/min/mg mitochondrial protein respectively, were obtained for the two activities. Similar kinetic data for carnitine palmitoyl-transferase activity in intact mitochondria are a Km of 21 microM and a Vmax of 18.2 nmoles/min/mg mitochondrial protein. Only one activity of this enzyme could be detected in luteal mitochondria. It appears that the activities of both enzymes were not affected by prior administration of LH in vivo. The possibility that this negative finding was due to the experimental procedures employed, rather than a reflection of the situation in vivo, could not be discounted, although its more likely that these two enzymes are probably not locus of LH stimulation. The results indicate that fatty acid oxidation is an important metabolic capability of luteal mitochondria, and support the view regarding the lipid nature of the respiratory fuel of ovarian tissue.

Acyl-CoA synthetase activity of rat liver microsomes. Substrate specificity with special reference to very-long-chain and isomeric fatty acids

1. A fatty acid-depleted rat liver microsomal fraction has been used for the measurement of acyl-CoA synthetase (acid : CoA ligase (AMP-forming), EC 6.2.1.3) activity. The assay was based on measurement of the reaction product AMP by high-performance liquid chromatography (HPLC). The synthetase activity (V') revealed an optimum at 12 : 0 with saturated fatty acids as substrate, and at 14 : 1 with mono-unsaturated fatty acids. The apparent Michaelis constant, on the other hand, showed no systematic dependence on the fatty acid chain-length. 2. The mono-unsaturated fatty acids from 14 : 1 to 22 : 1 gave higher activities than the corresponding saturated fatty acids, and the relative differences were greatest with the very-long-chain fatty acids eicosaenoic (20 : 1 (11) (cis)) and docosaenoic acid (22 : 1 (11) (cis)). The synthetase activity with saturated and mono-unsaturated fatty acids was found to correlate to their capacity factor (k') on reversed phase chromatography (HPLC). This finding may indicate that the observed chain-length dependence of the activity largely reflects the partition of the fatty acids between a hydrophobic and a hydrophilic phase. In general, the position of the double bond and the cis/trans configuration had little effect on the V' values except for 22 : 1 (11)(cis) which revealed a 2-fold higher activity tha 22 : 1 (13) (cis). 3. The polyunsaturated fatty acid 22 : 6 (all cis) ;was notably found to be a much better substrate than other C22 fatty acids. 4. The present study does not support the idea of more than a single ATP-dependent acyl-CoA synthetase in the rat liver microsomal fraction.

Studies on acyl-CoA synthetase in rat arterial wall

The properties and characteristics of acyl-CoA synthetase from the arterial wall of rats were investigated. The enzyme is located mainly in the microsomes. Its activity was found to be maximal at pH 7.0-8.0, and to be completely dependent on ATP, CoASH and Mg2+. The Km values for these substances were the same as those of the enzyme in liver. The activity was affected by serum, divalent cations, albumin, lipoproteins and phospholipids. In rats, the activity was decreased in various pathological conditions, such as tocopherol deficiency, hypertension and diabetes mellitus and was increased in hypercholesterolemia. The physiological significance of this enzyme in free fatty acid metabolism is discussed on the basis of these results.

Studies on long chain fatty acid:CoA ligase from human small intestine

Long chain fatty acid:CoA ligase (EC 6.2.1.3.) was examined in human small intestinal mucosa using the hydroxamate-trapping method. With optimal assay requirements using palmitate as substrate a significant difference of specific activities could be detected in the total homogenate from duodenum, 40.9 +/- 11.6 nmol/min per mg protein versus upper jejunum, 51.9 +/- 13.7 (P less than 0.05). The enzyme activity of the microsomal fraction of upper jejunum was 101.8 +/- 44 nmol/min per mg protein. ATP, CoA, and Mg2+ were essential constituents of the reaction. A broad pH-optimum was observed between 6.75 and 7.75 with a maximum at a pH of 7.25. Whereas palmitate in the presence of albumin revealed a wide range of optimal concentration in supporting maximal enzyme activity, oleate was found to strongly inhibit the reaction. Where substrate specificity with both the total homogenate and the microsomal fraction was concerned, maximal reaction rates were obtained with palmitate for the long chain saturated fatty acids C12:0' C14:0' C16:0' and C18:0' and with oleate for the long chain unsaturated fatty acids C18:1 C18:2' and C18:3' respectively. The highest specific activity of the enzyme was localised in the microsomal fraction. The kinetic data and properties of the long chain fatty acid: CoA ligase from human intestine are discussed with respect to the intestinal enzyme from other species.

Utilization of endogenous diacylglycerol for the synthesis of triacylglycerol, phosphatidylcholine and phosphatidylethanolamine by lipid particles from baker's yeast (Saccharomyces cerevisiae)

The activity of the enzymes diacylglycerol acyltransferase (EC 2.3.1.20), cholinephosphotransferase (EC 2.7.8.2) and ethanolaminephosphotransferase (EC 2.7.8.1) have been measured in a lipid particle preparation from baker's yeast (Saccharomyces cerevisiae) with endogenous 1,2-diacylglycerol as substrate. For all three enzymes the rate of diacylglycerol utilization was established with respect to substrate and Mg2+ concentration. Neither of the enzyme activities was stimulated significantly by addition of diacylglycerols. The conversion of diacylglycerol into triacylglycerol in the presence of CDP-choline and CDPethanolamine, and the synthesis of phospholipids in the presence of acyl-CoA either added or generated in situ were studied. Neither CDPcholine nor CDPethanolamine had an effect on triacylglycerol synthesis. Exogenous acyl-CoA had no effect on either choline- or ethanolaminephosphotransferase activity. However, when the necessary substrates for formation of acyl-CoAs in situ (ATP, CoA, Mg2+ and free fatty acids) were added a decrease in both cholinephosphotransferase and ethanolaminephosphotransferase activity was observed. This inhibition was shown to be due to ATP and might explained as a result of chelation of the Mg2+, a necessary activator of both the choline- and the ethanolaminephosphotransferase.

A study of assay conditions for palmitoyl-CoA synthetase and carnitine palmitoyltransferase in homogenates of human blood platelets

The assay conditions for palmitoyl-CoA synthetase (P-CoA S) and carnitine palmitoyltransferase (CPT) in homogenates of human blood platelets have been studied. The assay based on trapping of palmitoyl-CoA by carnitine in the presence of exogenous CPT gave higher activity of P-CoA S than the assay based on direct isolation of the palmitoyl-CoA formed. The activity of CPT was higher on exogenous palmitoyl-CoA than on endogenous palmitoyl-CoA formed from palmitic acid and CoA in the presence of endogenous P-CoA S. The activity of CPT was strongly dependent on the incubation time and the amount of platelets used. The initial activity of this enzyme in human blood platelets was higher than previously assumed.

Acyl-coenzyme-A synthetase I from Candida lipolytica. Purification, properties and immunochemical studies

Acyl-coenzyme-A synthetase I from Candida lipolytica has been purified to homogeneity as evidenced by polyacrylamide gel electrophoresis in the presence and absence of dodecylsulfate as well as by Ouchterlony double-diffusion analysis. The purification procedure involves resolution of cellular particles with Triton X-100 and chromatography on phosphocellulose, Blue-Sepharose and Sephadex G-100. The purified enzyme exhibits a specific activity of 20--24 U/mg protein at 25 degree C, which is about 100-fold higher than those of long-chain acyl-CoA synthetases hitherto reported. The molecular weight of the enzyme has been estimated by polyacrylamide gel electrophoresis in the presence of dodecylsulfate to be approximately 84 000. The enzyme is specific for fatty acids with 14--18 carbon atoms regardless of the degree of unsaturation. Studies with the use of specific antibody to acyl-CoA synthetase I have indicated that this enzyme is immunochemically distinguishable from acyl-CoA synthetase II.

Synthesis of acyl-S-pantetheine by rat liver microsomes

The synthesis of acyl-S-pantetheine was found to occur in rat liver microsomal preparations. The reaction required ATP and a metal ion as cofactors, a fatty acid and the reduced form of pantetheine for optimal activity. The Km for pantetheine was 0.8 mM, for ATP 0.8 mM, and for oleic acid 0.3 mM. Mg2+ (20mM), Mn2+ (5 mM), Ca2+ (5mM), and Fe2+ (5 mM) produced approximately equal activity when all other conditions were optimal. The characterization of the product and other properties of the enzyme are described. The acyl-S-pantetheine formed does not act as an acyl donor in the acylation of sn-glycerol-3-phosphate, 1,2-diacylglycerol, or lysolecithin.