Showing papers on "Acyl-CoA published in 1993"

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

Abstract: 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.

Peroxisomal beta-oxidation is a significant pathway for catabolism of fatty acids in a marine teleost

Abstract: Hepatic beta-oxidation is characterized in a marine teleost, Myoxocephalus octodecimspinosus, to determine mitochondrial and peroxisomal substrate selectivity as well as metabolic partitioning. Substrate selectivity is broad for peroxisomal beta-oxidation. Acyl CoA oxidase activities, with all unsaturated substrates measured, are at least 35% of activity with palmitoyl CoA (16:0), a saturated substrate. Mitochondrial selectivities are more pronounced. Carnitine palmitoyltransferase activity with a monounsaturate, palmitoleoyl CoA (16:1), is nearly 40% greater than activity with palmitoyl CoA, whereas activities with two polyunsaturates are < 10% of activity with the saturate. The presence of polyunsaturated acyl CoA esters inhibits up to 70% the oxidation of palmitoyl CoA by intact peroxisomes. Acyl CoA hydrolase activity is localized to peroxisomal fractions prepared by density-gradient centrifugation. Hydrolytic activity in these fractions is nearly twofold the activity of beta-oxidation. Estimates for metabolic partitioning suggest that at least 50% of hepatic beta-oxidation may be initiated by the peroxisomal compartment.

UDPglucose: fatty acid transglucosylation and transacylation in triacylglucose biosynthesis.

Abstract: Glandular trichomes of the wild tomato Lycopersicon pennellii Corr. (D'Arcy) secrete large amounts of 2,3,4-tri-O-acylglucoses possessing straight- and branched-chain fatty acids of short to medium chain length (C4-C12). Although previous biosynthetic studies suggested that glucose acylation proceeded via acyl CoA intermediates, repeated attempts to demonstrate isobutyryl-CoA-dependent glucose acylation were unsuccessful. When [14C]isobutyrate is administered to detached L. pennellii leaves, the label is readily converted to 1-O-isobutyryl-beta-D-glucose. This is immediately followed by the appearance of di- and triacylated glucose esters. L. pennellii extracts catalyzed the formation of 1-O-isobutyryl-beta-D-glucose from isobutyrate and UDPglucose, and detached L. pennellii trichomes catalyzed transfer of the isobutyryl moiety from synthetic 1-O-isobutyryl-beta-D-glucose to D-glucose. Detached L. pennellii trichomes also catalyzed the formation of diacylglucose and triacylglucose via transfer of the isobutyryl moiety from 1-O-[14C]isobutyryl-beta-D-glucose to mono- or diacylglucoses, respectively. These studies suggest a multistep mechanism in which activation of fatty acids to their respective high-energy 1-O-acyl-beta-D-glucopyranose derivatives is followed by transfer of the 1-O-acyl moiety to non-anomeric positions of other glucose and/or partially acylated glucose molecules. This appears to be the primary mechanism of activation and fatty acid esterification to glucose in L. pennellii trichomes. Cultivated tomato, L. esculentum Mill., also activates free fatty acids to their 1-O-acyl-beta-D-glucose derivatives but lacks the acyl transfer mechanism for synthesizing polyacylated sugars.

CoA and fatty acyl-CoA derivatives mobilize calcium from a liver reticular pool.

Abstract: The effect of CoA and fatty acyl-CoA esters on Ca2+ fluxes has been studied in isolated liver microsomes and in digitonin-permeabilized hepatocytes. When microsomes were loaded with increasing concentrations of Ca2+ (6-29 nmol/mg of protein), the extent to which CoA and palmitoyl-CoA released Ca2+ increased. At 23 nmol of Ca2+/mg of protein, half-maximal [CoA] and [palmitoyl-CoA] were 35 and 50 microM respectively. Under conditions of minimal Ca2+ loading, net release of Ca2+ was absent, but Ca2+ translocation from a CoA-sensitive to a CoA-insensitive pool took place. The effect of CoA required the presence of fatty acids, probably to form fatty acyl esters. In permeabilized hepatocytes, the pool(s) mobilized by CoA (or by palmitoyl-CoA) appeared to be different from that mobilized by Ins(1,4,5)P3.

Reversal of the adverse chronic effects of the unsaturated derivative of valproic acid--2-n-propyl-4-pentenoic acid--on ketogenesis and liver coenzyme A metabolism by a single injection of pantothenate, carnitine, and acetylcysteine in developing mice.

Abstract: Like treatment with the parent compound valproic acid (VPA), acute and/or chronic treatment with the unsaturated derivative, 2-n-propyl-4-pentenoic acid (4-en-VPA), decreased ketogenesis and lowered free CoA, acetyl CoA, and free carnitine levels in the livers of normal developing mice. Concomitantly, there were manifold increases in the content of medium-chain acyl CoA esters (4-en-VPA CoA and 4-en-VPA CoA metabolites). Acute cotreatment of 4-en-VPA-treated animals with pantothenate, carnitine, and acetylcysteine caused significant amelioration of these metabolic aberrations. In animals chronically treated with 4-en-VPA, a single injection of pantothenate, carnitine, and acetylcysteine returned the 4-en-VPA-depressed levels of β-hydroxybutyrate in plasma and free CoA and acetyl CoA in liver to normal. These findings support the hypothesis that VPA-and 4-en-VPA-induced hepatic dysfunction is produced by CoA sequestration rather than by irreversible inhibition by alkylation of the enzymes of fatty acid β-oxidation by reactive intermediates. The findings also support the important but little-known role of carnitine in CoA metabolism—carnitine relieves the inhibition of pantothenate kinase, the rate-controlling first enzyme in the pathway of CoA synthesis by its product, free CoA, and by CoA esters.

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

Abstract: 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. (Mol Cell Biochem20: 89–94, 1993)

Differential effects of fatty acyl coenzyme A derivatives on citrate synthase and glutamate dehydrogenase.

Abstract: We investigated the hypothesis that one mechanism underlying fatty acid toxicity is the selective inhibition of rate-limiting and/or regulated tricarboxylic acid cycle and related enzymes by fatty acyl coenzyme A (CoA) derivatives by examining the effects of several fatty acyl CoAs on purified citrate synthase (CS) and glutamate dehydrogenase (GDH). The results indicate that, at pathophysiological levels, palmitoyl CoA, a long-chain acyl CoA, is a potent inhibitor of CS and GDH with IC50 values of 3-15 microM. At much higher levels (in the pathological and toxicological range), octanoyl and decanoyl CoA (medium-chain acyl CoAs) inhibited both enzymes with IC50 values of 0.4-1.6 mM. Butyryl CoA, a short-chain acyl CoA, inhibited CS (IC50 = 0.9 mM) at toxicological levels but inhibited GDH poorly. These results suggest that the long-chain fatty acyl CoA inhibition of CS and GDH may assume some pathophysiological importance in fatty acid toxicity and in metabolic encephalopathies in which organic acidemia is persistent. The findings also provide additional support for the original hypothesis.

The hypolipidemic effects of 2-furoic acid in Sprague-Dawley rats.

Abstract: 2-Furoic acid was shown to be effective in lowering both serum cholesterol and serum triglyceride levels significantly in rats with an elevation of HDL cholesterol level at 20 mg/kg/day orally. LDL receptor activity was reduced in hepatocytes, aorta foam cells, small intestinal epithelium cells and fibroblasts. HDL receptor activity was elevated in the rat hepatocytes and small intestinal cells. These activities were correlated with inhibition of acyl CoA cholesterol acyl transferase activity. Neutral cholesterol ester hydrolase activity was elevated in rat hepatocytes and human fibroblasts. Thus, 2-furoic acid appears to interfere directly with activity of intracellular enzymes rather than affecting high affinity-mediated lipoprotein membrane receptors. In vivo treatment with 2-furoic acid led to reduction in the liver and small intestine ATP dependent citrate lyase, acetyl CoA synthetase, acyl CoA cholesterol acyl transferase, sn-glycerol 3-phosphate acyl transferase, phosphatidylate phosphohydrolase and heparin induced lipoprotein lipase activities. 2-Furoic acid reduced biliary cholesterol levels but the agent increased bile salts which are lithogenic. Acute toxicity studies in mice suggest that the agent has some hepatic toxicity effects. The LD50 was relatively low at 250 mg/kg IP in mice.

[Non-ketotic hypoglycemia caused by carnitine palmitoyl transferase 1 deficiency]

Abstract: A 9-year-old girl was referred to our hospital after recurrent episodes of hypoglycemia, altered consciousness and persistent vomiting without acetonemia or myopathic symptoms. Other pertinent laboratory data included elevated BUN, hyperammonemia and very low levels of triglycerides with elevated free fatty acids. The patient was born from unaffected but related parents (second cousins) and the illness was previously diagnosed as Reye encephalopathy. Recurrence of similar attacks suggested an underlying metabolic disorder. Several syndromes of impaired FFA beta oxidation were taken into account and discarded successively after laboratory investigations: systemic carnitine deficiency, Medium and Long Chain Acyl-CoA Dehydrogenase deficiency and Multiple Acyl CoA Dehydrogenation deficiency (Glutaric aciduria, Ethylmalonic-adipic aciduria and riboflavin-responsive multiple acyl CoA dehydrogenation deficiency). Urinary and hematic gas-chromatography and Mass-Spectrometry show no abnormality in Medium Chain fatty acids and in C6-C10 dicarboxylic acids. Carnitine plasma concentrations (both total and free) were above normal levels while in urine acetyl carnitine was low in respect to longer acyclic radicals. Among metabolic defects located at the level of hepatic fatty acid oxidation, only Carnitine Transferase deficiency can explain this peculiar mosaic of data (precursors of the blocked reaction are elevated in blood whereas lack of the metabolites derived uniquely from this reaction explains all the clinical manifestations).