Showing papers on "Acyl-CoA published in 1995"

Antarctic fish tissues preferentially catabolize monoenoic fatty acids

Abstract: Tissues of Antarctic marine fishes are very high in lipids, predominantly triacylglycerols (TAG). In addition to conferring static lift to these swimbladderless fishes, these rich lipid stores long have been considered as an important caloric resource to the animals. We have performed in vitro measurements of the rates of oxidation of 14C-labeled carbohydrates and fatty acids by oxidative skeletal muscle and heart ventricle of an Antarctic teleost, Gobionotothen gibberifrons to assess the relative importance of these substrates to aerobic energy metabolism. Capacities for regeneration of ATP calculated from oxidation rates of these fuels clearly indicate that fatty acids are more effective substrates of energy metabolism than either glucose or lactate with both tissues. Substrate competition experiments conducted between the saturated fatty acid palmitate (16:0) and the monoenoic unsaturate oleate (18:1) comparing the oxidation rate of radiolabeled fatty acid in the presence and absence of unlabeled competitor demonstrate a clear preference of both tissue types for catabolism of the monounsaturated substrate. Measurements of maximal activity of the putative flux-generating enzyme of mitochondrial β-oxidation, carnitine palmitoyltransferase (CPT), with a variety of fatty acyl CoA esters also show significant preference for a monoenoic fatty acyl CoA, palmitoleoyl CoA (16:1). The general pattern of results suggests that monounsaturated fatty compounds are the most readily utilized substrates for energy metabolism by oxidation muscle tissues of this Antarctic species. © 1995 Wiley-Liss, Inc.

Fatty acyl-CoA esters inhibit glucose-6-phosphatase in rat liver microsomes.

Abstract: In native rat liver microsomes glucose 6-phosphatase activity is dependent not only on the activity of the glucose-6-phosphatase enzyme (which is lumenal) but also on the transport of glucose-6-phosphate, phosphate and glucose through the respective translocases T1, T2 and T3 By using enzymic assay techniques, palmitoyl-CoA or CoA was found to inhibit glucose-6-phosphatase activity in intact microsomes The effect of CoA required ATP and fatty acids to form fatty acyl esters Increasing concentrations (2-50 microM) of CoA (plus ATP and 20 microM added palmitic acid) or of palmitoyl-CoA progressively decreased glucose-6-phosphatase activity to 50% of the control value The inhibition lowered the Vmax without significantly changing the Km A non-hydrolysable analogue of palmitoyl-CoA also inhibited, demonstrating that binding of palmitoyl-CoA rather than hydrolysis produces the inhibition Light-scattering measurements of osmotically induced changes in the size of rat liver microsomal vesicles pre-equilibrated in a low-osmolality buffer demonstrated that palmitoyl-CoA alone or CoA plus ATP and palmitic acid altered the microsomal permeability to glucose 6-phosphate, but not to glucose or phosphate, indicating that T1 is the site of palmitoyl-CoA binding and inhibition of glucose-6-phosphatase activity in native microsomes The type of inhibition found suggests that liver microsomes may comprise vesicles heterogeneous with respect to glucose-6-phosphate translocase(s), ie sensitive or insensitive to fatty acid ester inhibition

Fatty acyl CoA esters as regulators of cell metabolism.

Abstract: Long chain fatty acyl CoA esters have the ability to interact with certain proteins and thereby serve as effectors in cell metabolism. In particular, they can displace nucleotides from specific nucleotide dependent or binding proteins and interfere with their action. The ADP/ATP carrier and uncoupling protein are two examples where the interplay of nucleotide and acyl CoA binding to the proteins regulate their function. Other proteins such as glucokinase can be considered in this group. In certain tissues like liver they are affected during fasting and insulin deficiency, and when serum fatty acids and liver acyl CoA levels are elevated. More recently, an acyl CoA binding protein in E. coli has been found to be a transcription factor for gene regulation of fatty acid metabolism enzymes. There appears to be some consensus in the amino acid sequence for acyl CoA binding sites on these proteins which serve a variety of important roles in cellular metabolism.

Acyl-CoA binding and acylation of UDP-glucuronosyltransferase isoforms of rat liver: their effect on enzyme activity.

Abstract: When [14C]arachidonoyl-CoA was incubated with crude extracts of rat liver microsomes, [14C]arachidonic acid was incorporated into many proteins, suggesting that modification of these proteins with fatty acid, i.e. acylation, occurred. Using a [14C]arachidonyl-CoA labelling assay, 50 and 53 kDa proteins were purified from rat liver microsomes to near homogeneity by sequential chromatography on Red-Toyopearl, hydroxyapatite, heparin-Toyopearl, Blue-Toyopearl and UDP-hexanolamine-agarose. Acylation of the 50 and 53 kDa proteins occurred in the absence of any other protein, suggesting that these molecules catalyse autoacylation. The acylation was dependent on the length of the incubation period and the concentration of [14C]arachidonoyl-CoA. The 50 and 53 kDa proteins also had acyl-CoA-binding activity; initial rates of acyl-CoA binding and acylation were 0.25 and 0.004 min-1 respectively. The proteins also had weak but distinct acyl-CoA-hydrolysing activity (0.006 min-1). These results suggest that the proteins catalysed the sequential reactions of binding to acyl-CoA, autoacylation, and hydrolysis of fatty acid. N-terminal amino acid sequencing analysis showed these proteins to be UDP-glucuronosyltransferase (UDPGT) isoforms. UDPGT activity was inhibited by arachidonoyl-CoA. These results suggest that binding of acyl-CoA and acylation of UDPGT isoforms regulate the enzyme activities, implying a possible novel function for fatty acyl-CoA in glucuronidation, which is involved in the metabolism of drugs, steroids and bilirubin.

Activity measurements of acyl-CoA oxidases in human liver

Abstract: Peroxisomal β-oxidation is involved in the degradation of different fatty acids or fatty acid derivatives including eicosanoids (prostaglandins, leukotrienes, thromboxanes), dicarboxylic fatty acids, very long-chain fatty acids, pristanic acid, bile acid intermediates (di- and trihydroxycoprostanoic acids), and xenobiotics. Separate β-oxidation systems are probably active inside peroxisomes, each acting on a distinct set of substrates, as suggested by the discovery of multiple acyl-CoA oxidases.

Photoaffinity Labeling of Developing Jojoba Seed Microsomal Membranes with a Photoreactive Analog of Acyl-Coenzyme A (Acyl-CoA) (Identification of a Putative Acyl-CoA:Fatty Alcohol Acyltransferase.

Abstract: Jojoba (Simmondsia chinensis, Link) is the only plant known that synthesizes liquid wax. The final step in liquid wax biosynthesis is catalyzed by an integral membrane enzyme, fatty acyl-coenzyme A (CoA):fatty alcohol acyltransferase, which transfers an acyl chain from acyl-CoA to a fatty alcohol to form the wax ester. To purify the acyltransferase, we have labeled the enzyme with a radioiodinated, photoreactive analog of acyl-CoA, 12-[N-(4-azidosalicyl)amino] dodecanoyl-CoA (ASD-CoA). This molecule acts as an inhibitor of acyltransferase activity in the dark and as an irreversible inhibitor upon exposure to ultraviolet light. Oleoyl-CoA protects enzymatic activity in a concentration-dependent manner. Photolysis of microsomal membranes with labeled ASD-CoA resulted in strong labeling of two polypeptides of 57 and 52 kD. Increasing concentrations of oleoyl-CoA reduced the labeling of the 57-kD polypeptide dramatically, whereas the labeling of the 52-kD polypeptide was much less responsive to oleoyl-CoA. Also, unlike the other polypeptide, the labeling of the 57-kD polypeptide was enhanced considerably when photolyzed in the presence of dodecanol. These results suggest that a 57-kD polypeptide from jojoba microsomes may be the acyl-CoA:fatty alcohol acyltransferase.

Effects of CoA and acyl-CoA on Ca(2+)-permeability of endoplasmic-reticulum membranes from rat liver.

Abstract: We have studied the effects of CoA and palmitoyl-CoA on Ca2+ movements and GTP-dependent vesicle fusion in rat liver microsomes. (1) Inhibition of membrane fusion by CoA depends on esterification of CoA to long-chain acyl-CoA using endogenous non-esterified fatty acids. (2) Binding of long-chain acyl-CoA to microsomal membranes is inhibited by BSA, which also relieves inhibition of membrane fusion. (3) Under conditions where acyl-CoA binding is inhibited, CoA causes increased Ca2+ accumulation, apparently by decreasing the Ca2+ leak rate. (4) Conversely, palmitoyl-CoA, in the presence of BSA, causes Ca2+ efflux. (5) The decrease in Ca(2+)-permeability caused by CoA does not depend on the presence of ATP or GTP, and is irreversible in the short term. (6) Using 14C-labelled CoA we show that CoA derivatives can be formed from endogenous components of microsomal membranes in the absence of ATP. (7) The results are interpreted in terms of a Ca(2+)-permeability which is controlled by CoA and/or long-chain acyl-CoA esters.

Erythrocyte membrane reacylation in juvenile neuronal ceroid‐lipofuscinosis: Measurement of membrane‐bound carnitine palmitoyl transferase, acyl‐CoA synthetase, and lysophospholipid: Acyl‐CoA acyltransferase activities

Abstract: In order to study the biochemical mechanisms responsible for the membrane fatty acid deficiency in juvenile neuronal ceroid-lipofuscinosis, we have analyzed the reacylation pathway in isolated erythrocyte membranes in 5 patients. We studied membrane carnitine palmitoyl transferase, and developed a combined assay to study acyl-CoA synthetase and lysophospholipid acyl-CoA acyltransferase activities. There were no significant differences between control and patient membranes, suggesting that abnormalities in these 3 putative candidate enzymes are not responsible for the disease.

Identification of Jojoba Seed acyl-CoA:Fatty Alcohol Acyltransferase by Photolabeling with acyl-CoA Analog

Abstract: The desert shrub jojoba (Simmondsia chinensis, Link) appears to be the only plant system that synthesizes large quantities of liquid wax. Two enzymes are specific to the wax biosynthetic pathway: fatty acyl-CoA reductase, which catalyzes the NADPH-specific reduction of the fatty acyl moiety of acyl-CoA to fatty alcohol, and acyl-CoA:fatty alcohol acyltransferase, which catalyzes the coupling of fatty acid to fatty alcohol.

Accumulation of fatty acids and their carnitine derivatives during myocardial ischemia

Abstract: Fatty acids are important substrates for the heart. Under normal conditions fatty acids are continuously extracted from the extracellular space, transported through the cytoplasm to the mitochondria by fatty acid-binding proteins (FABP), and converted to fatty acyl CoA. Part of acyl CoA is used for the formation of complex lipids (triacylglycerols and phospholipids), the majority of the acyl residues is channeled across the mitochondrial inner membrane into the mitochondrial matrix with the use of a carnitine-mediated transport system [1].

Comparison of metabolic fluxes of cis-5-enoyl-CoA and saturated acyl-CoA through the beta-oxidation pathway.

Abstract: The metabolic fluxes of cis-5-enoyl-CoAs through the beta-oxidation cycle were studied in solubilized rat liver mitochondrial samples and compared with saturated acyl-CoAs of equal chain length. These studies were accomplished using either spectrophotometric assay of enzyme activities and/or the analysis of metabolites and precursors using a gas chromatographic method after conversion of CoA esters into their free acids. Cis-5-enoyl-CoAs were dehydrogenated by acyl-CoA oxidase or acyl-CoA dehydrogenases at significantly lower rates (10-44%) than saturated acyl-CoAs. However, enoyl-CoA hydratase hydrated trans-2-cis-5-enoyl-CoA at a faster rate (at least 1.5-fold) than trans-2-enoyl-CoA. The combined activities of 3-hydroxyacyl-CoA dehydrogenase and 3-ketoacyl-CoA thiolase for 3-hydroxy-cis-5-enoyl-CoAs derived from cis-5-enoyl-CoAs were less than 40% of the activity for the corresponding 3-hydroxyacyl-CoAs prepared from saturated acyl-CoAs. Rat liver mitochondrial beta-oxidation enzymes were capable of metabolizing cis-5-enoyl-CoA via one cycle of beta-oxidation to cis-3-enoyl-CoA with two less carbons. However, the overall rates of one cycle of beta-oxidation, as determined with stable-isotope-labelled tracer, was only 15-25%, for cis-5-enoyl-CoA, of that for saturated acyl-CoA. In the presence of NADPH, the metabolism of cis-5-enoyl-CoAs was switched to the reduction pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

ACYL CoA BINDING PROTEINS IN BRASSICA NAPUS L.: AMINO ACID SEQUENCE, GENES AND EXPRESSION

Abstract: Acyl-CoAs lie at the centre of lipid metabolism in developing seeds since they are the products of fatty acid synthesis by the plastid which are transferred to the ER where they act as substrates for triacylglycerol and phospholipid synthesis [2]. At present it is not clear how the acyl-CoAs are transported within the plant cell and whether the pool of acyl-CoAs resides free in the cytosol or is bound to membranes or proteins. Acyl CoA binding proteins (ACBP) were first reported by [1] as a factor which stimulated fatty acid synthesis in mammary gland extracts. They have been found subsequently in several animals, Drosophila and yeast. ACBPs are cytoplasmic proteins with an Mr of about 10 kDa and they have a very high affinity for binding long chain acyl-CoAs, but they do not bind fatty acids or CoA individually. The concentration of ACBP in some animal systems has been calculated to be higher than that of the acyl-CoA suggesting that the entire cellular pool of acyl-CoA is bound to ACBP. Over expression of the ACBP gene in yeast causes a corresponding increase in acyl-CoA concentration suggesting that the acyl-CoA pool size is influenced by the expression of ACBP genes. Some recent in vitro studies showed that phospholipid and TAG synthesis by microsomes isolated from rat liver are strongly influenced by the ratio of [ACBP] to [acyl-CoA]. When ACBP was in excess, TAG synthesis was strongly reduced but phospholipid synthesis remained unaffected. It is therefore important to determine whether ACBPs are present in plants.