Showing papers on "Acyl-CoA published in 1987"

Lipid and carbohydrate metabolism in the ischaemic heart

Abstract: Ischaemia has profound effects on myocardial metabolism and cell function in general High energy phosphate and glycogen stores are depleted Lactate, inorganic phosphate and hydrogen ions accumulate, exerting negative effects on the initially accelerated glycolytic flux Fatty acid oxidation is inhibited The cellular content of lipid intermediates, such as hydroxy-fatty acids, acyl CoA and acylcarnitine, increases in low-flow ischaemia hearts Non-esterified fatty acid (NEFA) accumulation occurs after 30–60 min ischaemia Endogenous triacylglycerol and phosphoglyceride turnover is most likely impaired, ultimately resulting in accumulation of lipid droplets in the oxygen deprived cells and in degradation of myocardial membranes Accumulated lipid substances such as NEFA, acyl CoA, acylcarnitine and lysophosphoglycerides, are likeley to be involved in the mechanism underlying ischaemia-induced damage to myocardial cells

Carnitine acyltransferases and acyl-CoA hydrolases in human and rat liver

Abstract: The activities of carnitine acyltransferases and acyl-CoA hydrolases were determined in human and rat liver to establish the validity of extrapolating from studies on rats to human metabolism. In human liver, carnitine acetyltransferase activity was 10-14 times higher and carnitine octanoyltransferase 1.7-2.4 times higher than in rat liver, while carnitine palmitoyltransferase activity was similar in human and rat. Acetyl-CoA hydrolase and octanoyl-CoA hydrolase activities were lower in human (42-57%) than in rat liver, but palmitoyl-CoA hydrolase activity was similar in both species. The activity of citrate synthase was lower (44%) in human than in rat liver. The low citrate synthase activity and the high carnitine acetyltransferase in human liver suggest that in man acetylcarnitine might be more important as a vehicle for export of acetyl units from mitochondria than citrate. The high activity of carnitine acetyltransferase in human liver is consistent with the observation that acetylcarnitine is the predominant acylcarnitine excreted in diabetic ketosis in man. It is concluded that the rat may not be a valid model for carnitine metabolism in man, and that in human liver carnitine may have an important role in transfer of acetyl groups out of mitochondria and possibly also to extra-hepatic tissues.

Detrimental actions of endogenous fatty acids and their derivatives. A study of ischaemic mitochondrial injury

Abstract: Functional and structural alterations of myocardial mitochondria were investigated after four conditions of myocardial ischaemia in guinea pig heart: (1) 45 min complete ischaemia, (2) 60 min low-flow anoxic perfusion (0.3 ml/g wet weight per minute) with a modified Tyrode solution, (3) as (2) with 0.4mM palmitic acid added to the perfusate, and (4) as (2) with 0.4 mM oleic acid added. Under conditions (1) and (2) the loss of tissue ATP (20–30% of aerobic control) and the degree of mitochondrial injury were similar. But when fatty acids were present during low-flow anoxia, ATP loss and mitochondrial injury were more severe. Oleic acid caused greater injury than palmitic acid. The extent of mitochondrial injury corresponded to variations in mitochondrial long-chain acyl CoA content. Compared to aerobic control values, acyl CoA was increased 1.5 fold under condition (1), not significantly altered under condition (2), increased 3.2 fold under condition (3) and increased 4.3 fold under condition (4). In low-flow anoxia fatty acids enhanced the depression of oxidative phosphorylation, the loss of cytochromes, the inhibition of adenine nucleotide translocase and the reduction of mitochondrial Ca2+ sequestration. Fatty acid induced injury differed in quality from that of conditions (1) and (2): complex II dependent respiration was markedly affected, cytochrome b was lost extensively, and cytochrome oxidase activity was distinctly reduced. The results indicate that fatty acids, when administered to ischaemic myocardium, interfere with mitochondrial membranes at several sites, probably by their CoA esters. The more lipophilic oleyl moiety has a greater effect than the palmityl moiety.

Hepatic CoA, S-acyl-CoA, biosynthetic precursors of the coenzyme and pantothenate-protein complexes in dietary pantothenic acid deficiency.

Abstract: Weanling rats were fed a pantothenic acid (PA)-free diet for 11 days. Although the animals did not show symptoms of vitamin deficiency, the concentrations of total and free CoA (analyzed with 2-oxoglutarate dehydrogenase), the levels of CoA, dephospho-CoA and 4'-phosphopantetheine (assayed together in the N-acetylation reaction) were decreased. As PA deficiency developed (by days 33-44 of the experiment), the reduction of the content of these metabolites and short-chain acyl-CoA became more pronounced. The level of long-chain acyl-CoA, the ratios of free CoA/total CoA and long-chain acyl-CoA/total CoA remained unchanged. The coenzyme biosynthetic precursors demonstrated the most marked response to the severity of PA deficiency. The relative stability of the hepatocyte CoA pool is interpreted in terms of the cytosol ability to deposit the vitamin in the form of pantothenate-protein complexes.

Acyl-CoA Elongation Systems in Allium porrum Microsomes

Abstract: The synthesis of very long chain fatty acids (VLCFA) has been demonstrated in cell-free preparations fron higher plants1,2,3. The leek epidermal cell microscme system is the best documented4,5,6 and it is in this system that the existence of an endogenous precursor ATP-dependent elongation system was established4. The elongation of exogenous acyl-CoAs in the absence of ATP has also been demonstrated5 and it was shown that acyl-CoAs were the reaction products of the acyl-CoA elongating system6. TCA and cerulenin inhibitory effects and in direct evidence suggest the presence of distinct C18-CoA and C2O-CoA elongating systems. In order to test this hypothesis, the elongation activities were solubilized.

Carnitine in Relation to Feeding Infants

Abstract: The importance of carnitine in facilitating long chain fatty acid oxidation and the importance of long chain fatty acid oxidation in energy metabolism of the infant are both well documented (1). Carnitine is therefore an important nutrient for the infant. However, the physiological processes in infant metabolism facilitated by carnitine may also include oxidation of medium chain fatty acids, catabolism of branched chain amino acids, thermogenesis, ketogenesis, utilization of ketone bodies, gluconeogenesis, prevention of hyperammonemia, prevention of accumulation of toxic concentrations of acyl CoA, and regeneration of free coenzyme A (2,3). The mechanism of carnitine action in many of these physiological processes remains to be elucidated.

Peroxisomal and mitochondrial fatty acid oxidation in human hepatoma cells (HEP-G2)

Abstract: Hep-G2 cells oxidize (1-/sup 14/C)palmitic acid (C16) and (1-/sup 14/C) lignoceric acid (C24) via beta-oxidation to /sup 14/CO/sub 2/ and water-soluble (WS) products. After perchloric acid precipitation and chloroform-methanol extraction, the WS fraction contained labelled oxidation products as well as fatty acyl CoA's, thus, measurement of WS radioactivity is an overestimate of Hep-G2 beta-oxidation. Alkaline hydrolysis of fatty acyl CoA's prior to measurement of WS radioactivity permits more accurate assessment of beta-oxidation. Using this method, the optimal pH for oxidation of each fatty acid to WS products by Hep-G2 cells was 9.0, while /sup 14/CO/sub 2/ production was maximal at pH 7.0. To determine the subcellular location of beta-oxidation, mitochondria (M) were partially separated from peroxisomes (P) on linear Nycodenz gradients. In Hep-G2 cells, oxidation of both C16 and C24 was observed mainly in fractions enriched in succinate dehydrogenase, an M marker enzyme. In contrast, both P and M of rat liver oxidized these fatty acids. However, when Hep-G2 cells were fractionated on discontinuous sucrose gradients, C16 and C24 were oxidized by both P and M fractions. They conclude that beta-oxidation of both long (C16) and very long (C24) chain fatty acids occurs in P as well as in Mmore » of Hep-G2 cells, and the present method reflects a more accurate and sensitive measurement of oxidation rates.« less

Effects of long-chain fatty-acyl esters of coenzyme A and carnitine on cell-free rat heart preparations

Abstract: The purpose of this study was to investigate the effects of fatty acyl CoA and carnitine esters on the glycolytic system of the rat heart. Using a respiring incubation mixture containing a whole-heart homogenate it was observed that oleoyl-CoA slowed down the glucose disappearance whereas lactate accumulation did not change. Experiments were also performed by means of an incubation mixture prepared with a soluble heart extract, considered to contain all glycolytic enzymes present in heart fibres. Palmitoyl-CoA or oleoyl-CoA as well as palmitoyl carnitine, added separately or together, were unable to alter the glucose disappearance and lactate accumulation in this mixture. These data suggest that long chain acyl-esters have not direct inhibitory actions on the heart glycolytic activity. However, CoA esters seem to exert indirect inhibitory effects which may be relevant to the myocardium under oxygen restriction situations.

Binding of acyl-CoA to liver fatty acid binding protein : effect on acytl-CoA synthesis

Abstract: The ability of purified rat liver and heart fatty acid binding proteins to bind oleoyl-CoA and modulate acyl-CoA synthesis by microsomal membranes was investigated. Using binding assays employing either Lipidex 1000 or multilamellar liposomes to sequester unbound ligand, rat liver but not rat heart fatty acid binding protein was shown to bind radiolabeled acyl CoA. Binding studies suggest that liver fatty acid binding protein has a single binding site acyl-CoA which is separate from the two binding sites for fatty acids. Experiments were then performed to determine how binding may influence acyl-CoA metabolism by liver microsomes or heart sarcoplasmic reticulum. Using liposomes as fatty acid donors, liver fatty acid binding protein stimulated acyl-CoA production, whereas that from heart did not stimulate production over control values. 14C-labeled fatty acid-fatty acid binding protein complexes were prepared, incubated with membranes, and acyl-CoA synthetase activity was determined. Up to 70% of the fatty acid could be converted to acyl-CoA in the presence of liver fatty acid binding protein but in the presence of heart fatty acid binding protein, only 45% of the fatty acid was converted. Liver but not heart fatty acid binding protein bound the acyl-CoA formed and removed it from the membranes. The amount of product formed was not changed by additional membrane, enzyme cofactors, or incubation time. Additional liver fatty acid binding protein was the only factor found that stimulated product formation. Acyl-CoA hydrolase activity was also shown in the absence of ATP and CoA. These studies suggest that liver fatty acid binding protein can increase the amount of acyl-CoA by binding this ligand, thereby removing it from the membrane and possibly aiding transport within the cell.