The inhibition of adenine nucleotide translocase activity by oleoyl CoA and its reversal in rat liver mitochondria

Improvement of myocardial function in diabetic rats after treatment with L-carnitine

The effects of L-carnitine administration on the severity of diabetes were investigated. Serum glucose, free fatty acids (FFA), triglycerides, and ketones from diabetic and normal rats injected for 2 weeks with 3 g/kg/d of either L-carnitine or saline were assayed. Hearts were analyzed for carnitine and long-chain acyl coenzyme A. L-carnitine treatment to diabetic rats significantly reduced serum glucose, FFA, triglycerides, and ketones. In nondiabetic rats, carnitine increased serum ketones while FFA and triglycerides were decreased. L-carnitine treatment to diabetic rats prevented a decrease in myocardial total carnitine content. Long-chain acyl carnitine increased while long-chain acyl coenzyme A decreased. In another experiment, L-carnitine administration (750 mg/kg/d for 14 days) significantly improved the recovery of cardiac output after 60, 90, and 120 minutes of ischemia in diabetic perfused hearts. These results suggest that L-carnitine therapy may reduce the severity of diabetes mellitus and improve myocardial performance.

Acyl-carnitine effects on isolated cardiac mitochondria and erythrocytes

The effects of various long-chain acyl-carnitines (AC) on mitochondrial functions and red cell membrane stability were studied. Lower concentrations slightly stimulate respiration-dependent functions such as phosphorylation rate and Ca++ uptake velocity, whereas higher concentrations inhibit these functions with concomitant depression of the ATP/O ratio. The order of effectiveness among the AC is very similar for different mitochondrial functions. The differences among AC in their actions on red cell stability in hypotonic media and their differences in influence on mitochondrial functions exhibit less resemblance. The relative order of erythrolytic concentrations of AC follows the order of their critical micellar concentrations. Model calculations indicate that the concentrations of AC found in ischemic hearts are below those which exhibit inhibitory effects in vitro. Ultrastructural changes in mitochondria incubated with AC are different from those found in ischemic tissue. From this, it seems questionable whether the elevated AC levels in ischemic hearts are indeed as important for the development of membrane damage as is often supposed.

Fatty acid oxidation intermediates and the effect of fasting on oxidation in red and white skeletal muscle

In vitro oxidation of U-[14C]glucose-6-phosphate, 2-[14C]pyruvate, and 1-[14C]pyruvate was significantly reduced in red skeletal muscle from fasting rats. Over the same time interval of fasting, 1-[14C]palmitate oxidation remained unchanged. Pyruvate dehydrogenase activity, assayed before in vitro activation, was also reduced in red muscle. Long chain acylcarnitine and long chain acyl CoA increased over the same time period in red muscle. Changes in long chain fatty acid derivatives and pyruvate oxidation were much less dramatic in white muscle. We propose that the rise in levels of long chain fatty acid derivatives may be directly related to the inhibition of carbohydrate oxidation during fasting in red skeletal muscle.

Regulation of citrate efflux from mitochondria of oleaginous and non-oleaginous yeasts by long-chain fatty acyl-CoA esters

1. Citrate efflux from a wide range of yeast mitochondria was inhibited by long-chain fatty-acyl-CoA esters. 2. Fatty-acyl-CoA esters with chain lengths of between 14 and 18 carbons were the most potent inhibitors of citrate efflux which was unaffected by the fatty acids themselves. 3. 50% inhibition of citrate transport was observed using palmitoyl-CoA and oleoyl-CoA at approx. 4-5 microM when the tricarboxylate carrier was saturated with L-malate as counter-anion. 4. The inhibition with palmitoyl-CoA and oleoyl-CoA was competitive with L-malate. 5. The possibility that the fatty-acyl-CoA esters were exerting their effect by acting as detergent was eliminated because of the low concentrations used and appropriate comparisons being made with non-specific detergents. Although detergents inhibited citrate efflux they also released citrate by causing membrane damage. 6. The effect of fatty-acyl-CoA esters on citrate efflux could be decreased by using higher mitochondrial protein levels and by adding bovine serum albumin. 7. The possibility is discussed that this inhibition represents a genuine feedback inhibition which could regulate the amount of lipid being synthesized by an oleaginous yeast.

The influence of linoleic acid intake on the kinetics of adenine nucleotide translocase

Dietary enrichment of mitochondrial polyenoic fatty acid content was associated with increased respiratory activity (Abuirmeileh and Elson). The influence of the membrane lipid composition on the adenine nucleotide translocase (AdNT) was studied in rats that were fed diets formulated with beef tallow (BT) to provide low or safflower oil (SO) to provide high contents of linoleic acid. The phosphatidylcholine/phosphatidylethanolamine ratio was 40% higher in the SO mitochondria due primarily to an increase in phosphatidylcholine. SO mitochondria exhibited 25% higher state 3 respiration, 50% higher state 4 respiration and 13% higher net ADP-dependent respiration than did the BT mitochondria. The relative RCR and ADP/O values of the SO mitochondria were slightly but significantly (p less than 0.01) lower. The kinetics of the AdNT were determined by the back exchange method (Pfaff and Klingenberg). At all assay temperatures, SO mitochondria exhibited a higher Km for ADP. However, addition of 5 mM carnitine to the assay mixture increased the affinity of the SO-AdNT giving Km values similar to that of the BT-AdNT. Washing the mitochondria with fat-free BSA had a similar, but lesser, effect. At 25 C and 37 C, the Vmax of the SO-AdNT were increased by 11-15% (p less than 0.05) which was independent of either BSA-wash or the presence of carnitine. According to Dixon plot studies, the SO-AdNT had a comparable Ki for atractylate but a slightly lower Ki for palmitoyl-CoA inhibition. The accumulation of acyl-CoA esters in the SO mitochondria was not ruled out. The overall results suggest that changes in mitochondrial membrane lipids accommodated an increased Vmax of the SO-AdNT, which in turn accounted for that part of the increased state 3 respiration dependent on ADP translocation.

Switch on and switch off phenomenon of liver gluconeogenic function in lamprey (Lampetra fluviatilis L.) under the influence of season and temperature

The potential activity of pyruvate carboxylase in lamprey liver is the same as in mammals. However, at certain stages of the life cycle this reaction does not take place because of ATP deficiency in mitochondria. Energy charge potential of liver cells ranges from 0.76 to 0.11 throughout a year. Heat adaptation of lampreys leads to a rapid increase of the ATP level and of the NAD+/NADH ratio in liver. The intensity of gluconeogenesis and glycogen levels are also enhanced. Cold reacclimation reverses the effect. A scheme accounting for the temperature changes in energy status of hepatocytes has been proposed.

Distinctive roles of oleate and glucagen in gluconeogenesis

1. The effect of oleate on the subcellular distribution of ATP, 2-oxoglutarate, glutamate, citrate, malate and phosphoenolpyruvate was studied in hepatocytes from rats starved for 48 h by applying a modified digitonin method. The results markedly differ from those observed after glucagon [Siess, E. A., Brocks, D. G., Lattke, H. K., and Wieland, O. H. (1977) Biochem J. 166, 225-235]. Total cellular amounts and the distribution of ATP and 2-oxoglutarate remained unchanged. In the mitochondrial matrix glutamate was increased, while mitochondrial phospho-enolpyruvate was decreased. Citrate and malate were increased both in the mitochondrial and cytosolic space. 2. In contrast to the effect of glucagon, gluconeogenesis from dihydroxyacetone, fructose or glutamine was not stimulated by oleate. Gluconeogenesis from propionate was even inhibited by the fatty acid. 3. The stimulation by glucagon of glucose production from dihydroxyacetone or fructose was undiminished in biotin-deficient hepatocytes. Glucose formation from lactate, however, was stimulated only in biotin-substituted hepatocytes. 4. The results indicate that oleate stimulates gluconeogenesis by increasing pyruvate carboxylase activity (EC 6.4.1.1), whereas glucagon displays a more complex mode of action.

Inhibition of adenine nucleotide translocase by oleoylcarnitine, oleoylcoa and oleate in isolated arterial mitochondria

Adenine nucleotide translocase (AdNT) activity was studied in isolated mitochondria from normal rabbit aortas. The enzyme was inhibited by oleic acid, oleoylCoA, and oleoylcarnitine with 50% inhibition occurring at 5 muM, 6 muM and 14 muM, respectively (corresponding to 8, 10, and 23 nmol/mg protein). PalmitoylCoA and palmitoylcarnitine displayed similar potency to oleylCoA and oleoylcarnitine. The possibility that inhibition by fatty acid, acylCoA, and acylcarnitine could be attributed to non-specific detergency effects seems remote in that these compounds were more potent inhibitors of AdNT than equimolar concentrations of laurylsulfate. In addition, by use of the fluorescent probe N-phenyl-1-naphthylamine, it was shown that under the experimental conditions, inhibition of AdNT occurred at concentrations not exceeding a critical micelle concentration (CMC). Specificity was also suggested in that octanoylCoA was a weak inhibitor of AdNT and acetylcarnitine, butyrylcarnitine, cholesteryl oleate, and sphingomyelin were not inhibitory to the enzyme. In contrast to the observed inhibition of arterial AdNT by oleoylCoA and oleoylcarnitine, AdNT in isolated rabbit and rat heart mitochondria was inhibited only by oleoylCoA.

Comparison of the adenine nucleotide translocase in hepatomas and rat liver mitochondria

Various biochemical properties of the adenine nucleotide translocase were compared with mitochondria prepared from control and host liver, and Morris hepatomas 7777, 7800 and 5123C. The transport of phosphoenolpyruvate on the adenine nucleotide translocase was found to be three to four times more active, and inhibition of the transporter by palmitoyl-CoA and atractylate considerably less in hepatoma the active transport of phosphoenolypyruvate was associated with a greater stimulation of calcium egress from the mitochondria matrix by the anion in the hepatoma. The diminished sensitivity of the adenine nucleotide translocase to palmitoyl-CoA in hepatoma mitochondria was associated with lower levels of long chain acyl-CoA esters in the whole tissue. A change in activation energy at 6 degrees C for the adenine nucleotide translocase was found in host liver mitochondria while no break point in the temperature curve was observed in hepatoma mitochondria. These results are most consistent with a change in the structure-function relationship of hepatoma mitochondria due to differences in lipid composition.

On the capacity of the beta-oxidation of palmitate and palmitoyl-esters in rat liver mitochondria

The beta-oxidation of palmitate, palmitoyl-CoA and palmitoyl-L-carnitine proceeded at a high rate in isolated rat liver mitochondria. At high concentrations (100 nmol/mg protein) the oxidation of palmitate and palmitoyl-CoA was only partly carnitine dependent. All substrates were most rapidly oxidized in the presence of oxaloacetate and state 3 conditions. Succinate inhibited beta-oxidation especially in state 4 conditions. beta-Oxidation was faster in hypotonic than in isotonic medium both in state 3 and state 4 conditions. Hypertonicity inhibited beta-oxidation. The initial formation of palmitoyl-CoA from palmitate, CoA and ATP was faster than the oxidation of palmitate under identical conditions. The presence of bovine serum albumin inhibited the beta-oxidation, especially with palmitoyl-CoA or free palmitate as the substrates. Mitochondria contain a palmitoyl-CoA hydrolase which may influence the available intramitochondrial palmitoyl-CoA. The present results demonstrate no single rate limiting step in the beta-oxidation in vitro. Both the NADH/NAD ratio, competition for the respiratory chain, the level of ADP, binding of palmitoyl-CoA to extramitochondrial protein, and possibly intramitochondrial hydrolysis of palmitoyl-CoA all seem to influence the rate of beta-oxidation in vitro. It is suggested that in vivo the most important factor is the availability of acyl-CoA to the outer carnitine palmitoyl-transferase of the mitochondria.

Adenine nucleotide transport in sonic submitochondrial particles. Kinetic properties and binding of specific inhibitors

1. A procedure for preparation of sonic submitochondrial particles competent for adenine nucleotide transport is described. ADP or ATP transport was assayed, in the presence of oligomycin, in a saline medium made of 0.125 M KCl, 1 mM EDTA, 10 mM 4-morpholinopropane sulfonic acid buffer, pH 6.5. 2. Sonic particles transport ADP and ATP by an exchange diffusion process. Externally added ADP (or ATP) is exchanged with internal ADP and ATP with a stoichiometry of one to one. The V value for ADP transport 5 degrees C was between 2 and 3 nmol/min per mg protein. 3. The transport system in sonic particles is specific for ADP and ATP. It is strongly dependent on temperature. The activation energy between 0 and 9 degrees C is approx. 35 kcal/mol. The optimum pH is 6.5, 4, Like in intact mitochondria, externally added ADP is transported into sonic particles faster at a given concentration than externally added ATP. The V value for ADP transport is 1.5-2 times higher than the V value for ATP transport. 5. The transition from the energized to the deenergized state in sonic particles results in a decrease of the pH gradient across the membrane (internal pH less than external pH) and in a 2-4 fold increase in the Km value for ATP. This latter effect is opposite that found for transport of added ATP in intact mitochondria (Souverijn, J.H.M., Huisman, L.A., Rosing J. and Kemp, Jr., A. (1973) Biochim. Biophys. Acta 305, 185-198). Energization has no effect on the V value of ATP transport in sonic particles. 6. In contrast to intact mitochondria, inhibition of ADP transport in sonic particles by bongkrekic acid does not have any lag-time and does not depend on pH. The inhibition caused by bongkrekic acid is a mixed type inhibition with a Ki value of 1.2 micronM. Atractyloside and carboxyatractyloside do not inhibit ADP transport in sonic particles, unless the particles have been preloaded with these inhibitors during the sonication. 7. Palmityl-CoA added to sonic particles inhibits efficiently ADP transport. The mixed type inhibition found with palmityl-CoA has a Ki value of 1.6 micronM. 8. [3H]Bongkrekic acid binds to sonic particles readily and with high affinity. Bongkrekic acic binding to sonic particles does not depend on pH and it has a saturation plateau, corresponding approximately to 1.3 mol of site per mol of cytochrome a. The number of [3H]atracytloside binding sites is much lower (one-fifth of the bongkrekic acid). External carboxyatractyloside does not compete with [3H]bongkrekic acid for binding to sonic particles. However, when carboxyatractyloside is present inside the particles, it inhibits the binding of [3H]bongkrekic acid.

Interrelationship in the regulation of pyruvate dehydrogenase and adenine-nucleotide translocase by palmitoyl-CoA in isolated mitochondria

Full activation of rat liver pyruvate dehydrogenase in vitro by ADP was prevented by palmitoyl-CoA at a concentration sufficiently low to preclude substrate effects secondary to its oxidation by mitochondria. Activation of pyruvate dehydrogenase by ADP in livers of fat-fed rats was less than in the control animal. The results are consistent with the experiments demonstrating an inhibition of adenine nucleotide translocase and on increased intramitochondrial ATP/ADP ratio by palmitoyl-CoA which could account for the effect on pyruvate dehydrogenase. Inactivation of brain pyruvate dehydrogenase by ATP was also diminished by palmitoyl-CoA indicating that the effect was at the level of the adenine nucleotides rather than at either the pyruvate dehydrogenase kinase or phosphatase enzymes.

Effect of long-chain fatty acids and acyl-CoA on mitochondrial permeability, transport, and energy-coupling processes

The following effects of fatty acids and acyl-CoA thioesters on energy metabolism of mitochondria can now be assumed: (1) Inhibition of adenine nucleotide translocation. This effect may increase the energy state of mitochondria respiring under state 3 conditions and decrease phosphorylation potential in the surrounding medium (the cytoplasm). (2) Increased permeability to monovalent cations. This may lead to a partial energy dissipation due to a futile recycling of K+ (or another cation), namely and energy-dependent uptake and a passive outflow. (3) True uncoupling due to increased permeability to protons. This effect probably occurs at high concentrations of fatty acids only. (4) Substrate effect. Fatty acids in the form of acyl-CoA are excellent respiratory substrates for mitochondria of most tissues. Their oxidation is coupled to the generation of high energy state of the mitochondrial membrane and, consequently, to ATP synthesis.

Effects of thyroid hormone deficiency on the distribution of hepatic metabolites and control of pathways of carbohydrate metabolism in liver and adipose tissue of the rat

1. Measurements have been made of the hepatic metabolites in normal and thyroidectomized rats and enzymes of the glycolytic route, the pentose phosphate pathway, the tricarboxylic acid cycle and lipogenesis together with the flux of glucose through alternative pathways of glucose metabolism and into lipid. 2. There is a significant fall in the content of ADP, AMP, citrate, long-chain acyl-CoA derivatives and a rise of 3-phosphoglycerate, 2-phosphoglycerate and phosphoenolpyruvate following thyroidectomy. The observed changes in the glycolytic intermediates may be correlated with the increased activity of phosphofructokinase relative to pyruvate kinase and fructose bisphosphatase. 3. The NAD+/NADH quotient of the mitochondrial compartment, calculated from the reactants and Keq of 3-hydroxybutyrate dehydrogenase, becomes significantly more oxidized in hypothyroid animals. The redox state of the cytosolic NAD and NADP couples remains relatively unchanged. 4. The changes in the hepatic content of CoA derivatives and citrate and in the mitochondrial redox state are interpreted as indicating a depressed rate of lipid oxidation. 5. Calculations of the compartmentation of metabolites between the cytosol and mitochondria indicate a very marked decrease in mitochondrial citrate, 2-oxoglutarate and glutamate with smaller changes in aspartate and malate. These changes are interpreted as providing evidence for the importance of modifications in the malate-aspartate shuttle in hypothyroidism; this is further supported by measured changes in the distribution and activities of the component enzymes of the hydrogen shuttles. 6. There is a diminished activity of glucokinase and of enzymes of the glycolytic pathway below phosphofructokinase in livers from hypothyroid rats. The oxidative enzymes of the pentose phosphate pathway, ATP-citrate lyase, 'malic' enzyme and fatty acid synthetase also decrease markedly. There is a striking parallelism between the changes of enzyme profile of liver and adipose tissue in hypothyroidism. 7. Adrenal glands from hypothyroid rats showed a generalized delcine in enzyme activity in parallel with the fall in tissue weight. Cytosolic glycerol-3-phosphate dehydrogenase decreased sharply. 8. The present results are discussed in relation to data in the literature on the increased activities of cyclic AMP and cyclic GMP phosphodiesterases in hypothyroidism, observations which integrate the relationships between anabolic and catabolic pathways of carbohydrate and lipid metabolism with alterations in hormone sensitivity in hypothyroidism.

The inhibition of isocitrate oxidation by palmitoyl-l-carnitine and palmitoyl-C0 A in rat liver mitochondria

Palmitoyl-L carnitine decreases the oxidation of isocitrate in rat liver mitochondria in state 3 by 25-30%. Palmitoyl-L-carnitine acts as an additional substrate raising the rate of oxidative phosphorylation, NAD reduction and ATP/ADP ratio in mitochondria. Palmitoyl-CoA added to mitochondria oxidizing isocitrate in state 3 causes a strong inhibition of isocitrate oxidation and of oxidative phosphorylation and a considerable elevation of intramitochondrial NADH/NAD and ATP/ADP ratios. The effect of palmitoyl-CoA is dependent on its concentration and is competitive with ADP. Carnitine restores only oxidative phosphorylation, but the oxidation of isocitrate remains inhibited. Evidence is presented that the transport of isocitrate is not affected by palmitoyl-CoA is due to the inhibition of adenine nucleotide translocation. The kinetic studies of NAD-dependent isocitrate dehydrogenase in the soluble fraction of sonicated mitochondria revealed that the enzyme is very sensitive towards the inhibition by NADH and only very slightly affected by ATP (Ki for NADH and ATP are 0.017 and 3.6 mM respectively). On the basis of the kinetic data the relative contribution of NADH and ATP in the inhibition of isocitrate oxidation by fatty acids was calculated. It is concluded that the inhibition of isocitrate oxidation caused by palmitoyl-L-carnitine and palmitoyl-CoA is primarily due to the increased reduction of NAD, whereas the increase of ATP/ADP ratio is much less important.