Showing papers on "Acyl-CoA published in 1991"

Dietary polyunsaturated fatty acids modulate fatty acid composition and early activation steps of concanavalin A-stimulated rat thymocytes.

Abstract: The early biochemical responses to concanavalin A (Con A) of thymocytes from rats fed a saturated (coconut oil), (n-6) (sunflower oil) or (n-3) (fish oil) fatty acid-enriched diet for 3 wk were investigated. Fish oil feeding resulted in greater (n-3) polyunsaturated fatty acid level (PUFA) at the expense of (n-6) PUFA in total and individual thymocyte phospholipids. Such alterations of the fatty acid composition did not affect basal ornithine decarboxylase (ODC), cyclic nucleotide phosphodiesterase (PDE) or gamma-glutamyl transferase activities. However, the fish oil-enriched diet impaired some of the early thymocyte responses to Con A, such as the rapid induction (30 min) of soluble ODC and PDE activities. Synthesis of [3H]20:4(n-6) oxygenated metabolites was not different between the dietary groups; however, the uptake of [3H]20:4(n-6) into phospholipid classes was significantly lower in phosphatidylcholine and greater in phosphatidylethanolamine and phosphatidylinositol after fish oil feeding. Similarly, the Con A-induced remodeling of the [3H]20:4(n-6) esterification in phospholipids differed in sunflower oil- vs. fish oil-fed rats, suggesting a modulation of acyl CoA synthase and/or acyl CoA transferase activities. Thus, the modulation of Con A-induced ODC and PDE stimulation upon in vivo changes of membrane phospholipid fatty acid composition is not related to eicosanoid formation, but rather to the modification of the fatty acid acylation processes, altering phospholipid composition and signal transduction.

Do rat kidney cortex microsomes possess the enzymatic machinery to desaturate and chain elongate fatty acyl-CoA derivatives?

Abstract: Rat kidney cortex microsomal preparations were unable to catalyze Δ9, Δ6, and Δ5 desaturation of stearoylcoenzyme A (CoA), linoleoyl-CoA and dihomo-γ-linolenoyl-CoA, respectively. The kidney cortex microsomal fraction, however, did catalyze the malonyl-CoA dependent fatty acyl-CoA elongation. The biochemical properties of palmitoyl-CoA elongation were studied as a function of protein concentration, time, reduced nicotinamide adenine dinucleotide phosphate (NADPH), malonyl-CoA and substrate concentrations; of the substrates investigated, Δ6.9.12–18∶3 was the most active. Unlike what was observed in the hepatic system, a high-carbohydrate, fat-free diet did not induced kidney fatty acid chain elongation. All intermediate kidney cortex microsomal reactions,i.e., β-ketoacyl-CoA reductase, β-hydroxyacyl-CoA dehydrase andtrans-2-enoyl-CoA reductase activities, were significantly higher (greater than one order of magnitude) than the condensing enzyme activity, suggesting that the rate-limiting step in total elongation is the initial condensation reaction. Contrary to other reports, the results suggest that the kidney cannot synthesize arachidonic acid needed for eicosanoid production.

Phospholipid synthesis by chick retinal microsomes: fatty acid preference and effect of fatty acid binding protein.

Abstract: The acylation of 1-palmitoyl-sn-glycerophosphocholine (1-16∶0-GPC) or 1-palmitoyl-sn-glycerophosphoethanolamine (1-16∶0-GPE) was measured using the microsomal fraction prepared from retinas of 14–15-day-old chick embryos. Rates of incorporation of exogenously supplied fatty acids into diacyl-GPC were generally 5–7 times greater than into diacyl-GPE. Substrate preferences for incorporation into diacyl-GPC and diacyl-GPE were, respectively, 18∶2>18∶3=20∶5>20∶4>18∶1>22∶6=18∶0 and 18∶2>22∶6≽18∶3=18∶0≽20∶4=18∶1>20∶5. The apparent selectivities were not consistent with the reported fatty acid compositions of these lipid classes. The addition of partially purified fatty acid binding protein (FABP) to the reaction had no effect either on overall rates of incorporation or on the substrate preference. When fatty acyl-CoA substrates were used, rates of incorporation of the 18∶0 derivative were much higher than with the fatty acid, while rates with other fatty acyl-CoA were similar to those with the respective fatty acid. Substrate preferences for CoA derivatives incorporated into diacyl-GPC were: 18∶0>20∶4>18∶2≽22∶6, and into diacyl-GPE: 20∶4=22∶6>18∶0>18∶2. Polyunsaturated fatty acyl CoA (PUFA-CoA) were thus favored for incorporation into diacyl-GPE, and to a lesser extent into diacyl-GPC, a result that is consistent with composition data. When purified FABP was added to the reactions, there was an increase in the incorporation of 18∶0-CoA and a decrease or no change in the incorporation of PUFA-CoA. The deacylation/reacylation cycle thus appears to play a role in the modification of phospholipid composition. The data are not consistent, however, with a role for FABP in directing PUFA toward membrane lipid synthesis.

Inhibitors of metabolic reactions. Scope and limitation of acyl-CoA-analogue CoA-thioethers.

Abstract: Substrate and intermediate analogue inhibitors of enzymes were prepared in which the thioester oxygen of acyl-CoA substrates is replaced by hydrogen with formation of CoA-thioethers. Experiments performed with ATP citrate lyase and S-(3,4-dicarboxy-3-hydroxybutyl)-CoA are consistent with citryl-CoA but not with citryl-enzyme being the direct precursor of the products acetyl-CoA and oxaloacetate. Consistent with these results, a previously described isotopic exchange between acetyl-CoA and [3H]CoASH, indicating the formation of an acetyl-enzyme in the reaction pathway, could not be confirmed. Substrate analogue CoA-thioethers of malate synthase are inhibitors endowed with the affinity of the substrates. Acetyl carboxylase and fatty acid synthetase are not inhibited by the substrate analogue S-ethyl-CoA; S-carboxyethyl-CoA, which could substitute for malonyl-CoA, is likewise not inhibitory. An explanation is proposed. Previously suggested roles of S-carboxymethyl-CoA, an acetyl-CoA-related inhibitor of citrate synthase, are discussed in the light of new experimental data. S-Acetyl, S-propionyl and S-carboxymethyl derivatives of 1,N6-etheno-CoA loose the high affinity of their CoA-counterparts to citrate synthase, probably because the ethylene group prevents proper binding to the enzyme.

Inhibition of Glucuronidation of Benzo(a)pyrene Phenols by Long-Chain Fatty Acids

Abstract: Long-chain fatty acids inhibit glucuronidation of benzo(a)pyrene phenols in perfused liver; therefore, this study was designed to investigate interactions of fatty acids with β-glucuronidase, glucuronosyl transferase, and energy supply. In β-glucuronidase-deficient C3H/He mice, infusion of oleate (250 µm) increased the release of free benzo(a)pyrene phenols from 14 to 33 nmol/g/h and decreased release of glucuronides into the perfusate from 25 to 17 nmol/g/h. Rates of accumulation of glucuronides in the liver were also diminished from 11 to 4 nmol/g/h after infusion of oleate (250 µm). Fatty acids did not affect the release of benzo(a)pyrene metabolites into bile, and the ratio of free phenol to glucuronide production was increased from 0.57 to 1.30. A similar trend was observed in livers from DBA/2 mice that have β-glucuronidase. Rates of hydrolysis of benzo(a)pyrene-O-glucuronide were not altered in isolated microsomes by addition of oleoyl coenzyme A (CoA) or octanoyl CoA (10–∼100 µm). Thus, we conclude that fatty acids do not alter glucuronidation by acting on β-glucuronidase. The concentration of cofactors (UDP-glucuronic acid, UDP-glucose, and adenine nucleotides) involved in hepatic conjugation was not altered by infusion of concentrations of oleate (300 µm) that inhibited glucuronidation in perfused livers. When oleate concentrations were increased to 600 µm, UDP-glucuronic acid and UDP-glucose decreased 44 and 49%, respectively, and the ATP:ADP ratio declined concomitantly. Oleoyl CoA inhibited UDP-glucuronosyl transferase noncompetitively (half-maximal inhibition, 10 µm) in microsomes with 3-hydroxylbenzo(a)pyrene or p-nitrophenol as substrate. In contrast, octanoyl CoA was a very poor inhibitor of transferase activity. Inhibition of the transferase by oleoyl CoA was increased markedly by treatment with detergents (Triton X-100), i.e., half-inhibition of glucuronosyl transferase was obtained with about 2 µm oleoyl CoA. Inhibition of UDP-glucuronosyl transferase by oleoyl CoA was also increased in a dose-dependent manner by albumin, possibly due to increasing access of the CoA derivative to the enzyme. Collectively, these data indicate that fatty acids diminish glucuronidation via the formation of acyl CoA compounds that inhibit UDP-glucuronosyl transferase noncompetitively.