Aconitate Hydratase Activity Research Articles

The Key Enzymes of Carbon Metabolism and the Glutathione Antioxidant System Protect Yarrowia lipolytica Yeast Against pH-Induced Stress

In this study, we first thoroughly assayed the response of the key enzymes of energy metabolism and the antioxidant system in Yarrowia lipolytica yeast at extreme pH. The activity of the tricarboxylic acid cycle enzymes, namely NAD-dependent isocitrate dehydrogenase, aconitate hydratase, NAD-dependent malate dehydrogenase, and fumarate hydratase, NADPH-producing enzymes of glucose-6-P dehydrogenase and NADP-dependent isocitrate dehydrogenase, and the enzymes of the glutathione system was assessed. All the enzymes that were tested showed a significant induction contrary to some decrease in the aconitate hydratase activity with acidic and alkaline stress. It is probable that a change in the enzyme activity in the mitochondria matrix is involved in the regulation of the cellular metabolism of Y. lipolytica, which allows the species to prosper at an extreme ambient pH. It distinguishes it from any other type of ascomycete. A close relationship between the induction of the Krebs cycle enzymes and the key enzymes of the glutathione system accompanied by an increased level of reduced glutathione was shown. The assumption that the increased activity of the Krebs cycle dehydrogenases and promotion of the pentose phosphate pathway at pH stress launches a set of events determining the adaptive response of Y. lipolytica yeast.

Hepatotoxic doses of copper sulfate induce metabolic memory in the redox system, which has an age-dependent nature

Abstract. We tested the hypothesis that ageing is a consequence of the formation of metabolic memory and the possible role of the redox system as a basic, evolutionarily ancient system of metabolism regulation in stable metabolic patterns formation or metabolic states chronisation changed during adaptation. Three sequential intraperitoneal administration of copper sulfate to young (3-month-old Wistar rats) and old animals (20 months) at a dose of 1 mg/100 g of body weight (33% of the lethal dose) were used as adaptive inducers of the redox system. The amount of lipid hydroperoxides in mitochondria, cytosol in liver cells and blood serum, the activity of mitochondrial aconitate hydratase as an indicator of oxidative stress and the activity of a number of antioxidant enzymes were determined to assess the initial metabolic states, i. e. before exposure and 1, 30 and 60 days after exposure to copper sulfate on the body. It was shown that the amount of lipid hydroperoxides (LOOHs) in the liver mitochondria and blood serum of old rats before exposure to copper sulfate was more than 30% lower than in young animals, while the aconitase activity (an indicator of oxidative stress) was the same in animals of these ages. A lower amount of LOOHs coincided with an increased glutathione peroxidase activity in old animals. In old rats, the increased amount of LOOHs induced by copper ions was preserved even after eliminating copper from the body 30 days after administration. At the same time, it was restored to the original level in the young animals. The glutathione peroxidase and aconitase activity in mitochondria remained below the control values even after the inducer elimination, and this was age-depending. The obtained results do not contradict the hypothesis of metabolic memory's role in ageing mechanisms. We postulate a relationship between the duration of maintenance of altered metabolic patterns and the polyfunctionality of enzymes and other metabolites. _________________________________________________________________________________________ Keywords: ageing; redox system; metabolic memory; lipid hydroperoxides; antioxidant enzymes; chronic states.

SkQ1 improves immune status and normalises the activity of antioxidant and nadph-generating enzymes in adjuvant-induced rheumatoid arthritis in rats

Rheumatoid arthritis (RA) is a severe systemic autoimmune inflammatory disease. Oxidative stress and excessive formation of mitochondrial reactive oxygen species (ROS) are now considered to be the central pathogenetic mechanisms of connective tissue component destruction and the factors responsible for a highly active inflammatory process and autoimmune response. The aim of the present work was to evaluate the effect of mitochondrial-directed antioxidant 10-(6′-plastoquinonyl)decyltriphenylphosphonium (SkQ1) on immune status, intensity of free radical-induced oxidation and functioning of antioxidant system (AOS) and NADPH-generating enzymes in rats with adjuvant-induced RA. Laboratory animals were divided into 4 groups: a control group; a group of animals with RA; animals injected intraperitoneally with SkQ1 at a dose of 1250 nmol/kg every 24 hours during the next 8 days from day 7 of RA development, and animals given SkQ1 at a dose of 625 nmol/kg according to the above scheme. Material for the study was taken on day 15 after the start of the experiment. The rate of erythrocyte sedimentation, the level of circulating immune complexes, and the concentration of immunoglobulins A, M and G were determined in rats by enzyme immunoassay. The intensity of free radical-induced oxidation was assessed by iron-induced biochemiluminescence, diene conjugate content and aconitate hydratase activity. Enzyme activity and metabolite content in animal tissues were analysed spectrophotometrically. The results of the work showed that the development of RA was associated with an increase in the indicators of immune response and intensity of free radical-induced oxidation. The development of an imbalance in AOS functioning and an increase in the activity of NADPH-generating enzymes was also observed. The administration of SkQ1 resulted in a dose-dependent change in the oxidative status indicators towards the control, which was accompanied by the normalization of the immune status parameters. It seems that the tested compound decreased the level of mitochondrial ROS, resulting in an inhibition of the inflammatory response. The consequence of these changes could be inhibition of free radical generation by immunocompetent cells and subsequent mitigation of the severity of oxidative stress in the tissues.

SkQ1 Improves Immune Status and Normalizes Activity of NADPH-Generating and Antioxidant Enzymes in Rats with Adjuvant-Induced Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is a severe systemic autoimmune inflammatory disease. Oxidative stress and excessive formation of reactive oxygen species (ROS) by the mitochondria are considered as the central pathogenetic mechanisms of connective tissue destruction and factors responsible for a highly active inflammatory process and autoimmune response. The aim of this work was to evaluate the effect of mitochondria-targeted antioxidant 10-(6'-plastoquinonyl)decyltriphenylphosphonium (SkQ1) on the immune status, intensity of free radical-induced oxidation, and functioning of the antioxidant system (AOS) and NADPH-generating enzymes in rats with the adjuvant-induced RA. Laboratory animals were divided into 4 groups: control group; animals with RA; animals injected intraperitoneally with SkQ1 at the doses of 1250 and 625 nmol/kg, respectively, every 24 h for 8 days starting from day 7 of RA development. Tissue samples for analysis were collected on day 15 of the experiment. Erythrocyte sedimentation rate, the content of circulating immune complexes, and the concentration of class A, M, and G immunoglobulins were determined by enzyme immunoassay. The intensity of free radical-induced oxidation was evaluated based on the assessment of the iron-induced biochemiluminescence, diene conjugate content, and activity of aconitate hydratase. Enzymatic activity and metabolite content in the tissue samples were analyzed spectrophotometrically. It was shown that the development of RA was associated with an increase in the manifestation of immune response markers and intensity of free radical-induced oxidation, as well as with disruption of the AOS functioning and activation of NADPH-generating enzymes. SkQ1 administration resulted in a dose-dependent changes in the oxidative status indicators towards the control values and normalization of the immune status parameters. SkQ1 decreased the level of mitochondrial ROS, resulting in the suppression of the inflammatory response, which might cause inhibition of free radical generation by immunocompetent cells and subsequent mitigation of the oxidative stress severity in the tissues.

High Doses of Pesticides Induce mtDNA Damage in Intact Mitochondria of Potato In Vitro and Do Not Impact on mtDNA Integrity of Mitochondria of Shoots and Tubers under In Vivo Exposure.

It is well known that pesticides are toxic for mitochondria of animals. The effect of pesticides on plant mitochondria has not been widely studied. The goal of this research is to study the impact of metribuzin and imidacloprid on the amount of damage in the mtDNA of potato (Solanum tuberosum L.) in various conditions. We developed a set of primers to estimate mtDNA damage for the fragments in three chromosomes of potato mitogenome. We showed that both metribuzin and imidacloprid considerably damage mtDNA in vitro. Imidacloprid reduces the rate of seed germination, but does not impact the rate of the growth and number of mtDNA damage in the potato shoots. Field experiments show that pesticide exposure does not induce change in aconitate hydratase activity, and can cause a decrease in the rate of H2O2 production. We can assume that the mechanism of pesticide-induced mtDNA damage in vitro is not associated with H2O2 production, and pesticides as electrophilic substances directly interact with mtDNA. The effect of pesticides on the integrity of mtDNA in green parts of plants and in crop tubers is insignificant. In general, plant mtDNA is resistant to pesticide exposure in vivo, probably due to the presence of non-coupled respiratory systems in plant mitochondria.

1-benzoyl-6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline exerts a neuroprotective effect and normalises redox homeostasis in a rat model of cerebral ischemia/reperfusion.

Ischemia is one of the main etiological factors of stroke and is associated with the development of energy deficiency, oxidative stress, and inflammation. An abrupt restoration of blood flow, called reperfusion, can worsen the effects of ischemia. In our study, we assessed the neuroprotective potential of 1-benzoyl-6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline (BHDQ) in cerebral ischemia/reperfusion (CIR) in rats. Wistar rats, divided into 4 groups were used in the study: sham-operated animals; animals with CIR caused by occlusion of the common carotid arteries and subsequent removal of the occlusions; rats treated with BHDQ at a dose of 50mg/kg in the presence of pathology; sham-operated animals treated with BHDQ. The analysis of the state of energy metabolism in the brain, the level of the S100B protein and the histological assessment of the brain tissue were carried out. The antioxidant potential of BHDQ was assessed by measuring biochemiluminescence parameters, analysing the level of 8-isoprostane, products of lipid and protein oxidation, concentration of α-tocopherol and citrate, and aconitate hydratase activity during CIR in rats. A study of the effect of BHDQ on the regulation of the enzymatic antioxidant system and the inflammatory processes was performed. We demonstrated that BHDQ has a neuroprotective effect in CIR, reducing histopathological changes in the brain, normalizing pyruvate and lactate concentrations, and the transcripts level of Hif-1α gene. The positive effect of BHDQ was probably due to its antioxidant and anti-inflammatory activity, manifested in a decrease in the parameters of the oxidative stress, decreased mRNA of proinflammatory cytokines and NF-κB factor genes. In addition, BHDQ reduced the load on antioxidant protection enzymes, contributing to a change in their activities, decreased the level of antioxidant gene transcripts and expression of Nrf2 and Foxo1 factors toward control. Thus, BHDQ exhibited a neuroprotective effect due to a decrease in the level of oxidative stress and inflammation and the normalization of redox homeostasis on CIR in rats.

Dietary Mg2+ Intake and the Na+/Mg2+ Exchanger SLC41A1 Influence Components of Mitochondrial Energetics in Murine Cardiomyocytes.

Cardiomyocytes are among the most energy-intensive cell types. Interplay between the components of cellular magnesium (Mg) homeostasis and energy metabolism in cardiomyocytes is poorly understood. We have investigated the effects of dietary Mg content and presence/functionality of the Na+/Mg2+ exchanger SLC41A1 on enzymatic functions of selected constituents of the Krebs cycle and complexes of the electron transport chain (ETC). The activities of aconitate hydratase (ACON), isocitrate dehydrogenase (ICDH), α-ketoglutarate dehydrogenase (KGDH), and ETC complexes CI–CV have been determined in vitro in mitochondria isolated from hearts of wild-type (WT) and Slc41a1−/− mice fed a diet with either normal or low Mg content. Our data demonstrate that both, the type of Mg diet and the Slc41a1 genotype largely impact on the activities of enzymes of the Krebs cycle and ETC. Moreover, a compensatory effect of Slc41a1−/− genotype on the effect of low Mg diet on activities of the tested Krebs cycle enzymes has been identified. A machine-learning analysis identified activities of ICDH, CI, CIV, and CV as common predictors of the type of Mg diet and of CII as suitable predictor of Slc41a1 genotype. Thus, our data delineate the effect of dietary Mg content and of SLC41A1 functionality on the energy-production in cardiac mitochondria.

The Effect of 6-Hydroxy-2,2,4-Trimethyl-1,2-Dihydroquinoline on the Intensity of Free Radical Processes and Activity of Oxidative Metabolism Enzymes in Rats with Toxic Liver Injury

The effect of 6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline on markers of hepatocyte cytolysis (aspartate transaminase, alanine transaminase and gamma-glutamyl transpeptidase), parameters reflecting the state of oxidative status (intensity of biochemical luminescence and the content of conjugated dienes), and on activity of oxidative metabolism enzymes (aconitate hydratase, glucose-6-phosphate dehydrogenase, NADP-isocitrate dehydrogenase) was studied in rats with CCl4-induced liver injury. The results obtained in the course of this study demonstrate the ability of the test compound to reduce oxidative stress severity and the degree of liver cell damage, as well as to change activity of aconitate hydratase and NADP-generating enzymes towards control values. 6-Hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline was more effective in normalizing CCl4-induced changes of most analyzed parameters than carsil used as a reference compound. The tendency to normalize the state of oxidative status and enzyme activity of oxidative metabolism can be attributed to hepatoprotective and antioxidant properties of the test compound.

Influence of 10-(6-plastoquinonyl) decyltriphenylphosphonium on free-radical homeostasis in the heart and blood serum of rats with streptozotocin-induced hyperglycemia.

BACKGROUNDIt is known that under conditions of tissue tolerance to insulin, observed during type 2 diabetes mellitus (DM2), there is an increased production of reactive oxygen species. Moreover, the free radicals can initiate lipid peroxidation (LPO) in lipoprotein particles. The concentration of LPO products can influence the state of insulin receptors, repressing their hormone connection activity, which is expressed as a reduction of the glucose consumption by cells. It is possible that reduction in glucose concentration during administration of 10-(6-plastoquinonyl) decyltriphenylphosphonium (SkQ1) to rats with DM2 may be related to the antioxidant properties of this substance.AIMTo establish the influence of SkQ1 on free-radical homeostasis in the heart and blood serum of rats with streptozotocin-induced hyperglycemia.METHODSTo induce hyperglycemia, rats were fed a high-fat diet for 1 mo and then administered two intra-abdominal injections of streptozotocin with a 7-d interval at a 30 mg/kg of animal weight dose with citrate buffer equal to pH 4.4. SkQ1 solution was administered intraperitoneally at a 1250 nmol/kg dose per day. Tissue samples were taken from control animals, animals with experimental hyperglycemia, rats with streptozotocin-induced glycemia that were administered SkQ1 solution, animals housed under standard vivarium conditions that were administered SkQ1, rats that were administered intraperitoneally citrate buffer equal to pH 4.4 once a week during 2 wk after 1-mo high-fat diet, and animals that were administered intraperitoneally with appropriate amount of solution without SkQ1 (98% ethanol diluted eight times with normal saline solution). To determine the intensity of free radical oxidation and total antioxidant activity, we used the biochemiluminescence method. Aconitate hydratase (AH), superoxide dismutase, and catalase activities were estimated using the Hitachi U-1900 spectrophotometer supplied with software. The amount of citrate was determined by means of the Natelson method. Real-time polymerase chain reaction was carried out using an amplifier ANK-32.RESULTSIt was found that the mitochondrial-directed antioxidant elicits decrease of biochemiluminescence parameter values that increase by pathology as well as the levels of primary products of LPO, such as diene conjugates and carbonyl compounds, which indicate intensity of free radical oxidation. At the same time, the activity of AH, considered a crucial target of free radicals, which decreased during experimental hyperglycemia, increased. Apparently, increasing activity of AH influenced the speed of citrate utilization, whose concentration decreased after administering SkQ1 by pathology. Moreover, the previously applied anti-oxidant during hyperglycemia influenced the rate of antioxidant system mobilization. Thus, superoxide dismutase and catalase activity, as well as the level of gene transcript under influence of SkQ1 at pathology, were changing to the direction of control groups values.CONCLUSIONAccording to the results of performed research, SkQ1 can be considered a promising addition to be included in antioxidant therapy of DM2.

Effect of 6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline on the intensity of free radical processes and the activity of oxidative metabolism enzymes under toxic liver injury in rats

The effect of 6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline on markers of hepatocytes cytolysis (aspartate aminotransferase, alanine aminotransferase and gamma-glutamyl transpeptidase), parameters reflecting the state of oxidative status (intensity of biochemical luminescence and the content of diene conjugates), and the activity of oxidative metabolism enzymes (aconitate hydratase, glucose-6-phosphate dehydrogenase, NADP-isocitrate dehydrogenase) was studied in rats with CCl4-induced liver injury. The results obtained in the course of the work demonstrated the ability of the test compound to reduce the severity of oxidative stress and liver cells damage, as well as to change the activity of aconitate hydratase and NADP-generating enzymes in the direction of control values. 6-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline was more effective in normalizing CCl4-induced changes of the analyzed parameters that Carsil used as a reference compound. The tendency to normalize the state of oxidative status and enzyme activity of oxidative metabolism can attributed to hepatoprotective and antioxidant properties of the tested compound.

Effects of Melaxen and Valdoxan on Free-Radical Oxidation in Rat Heart with Experimental Hyperthyroidism

The rate of free-radical oxidation in rat heart with experimental hyperthyroidism (EH) was estimated after Melaxen and Valdoxan administration. It was found that the content of protein carbonyl groups increased if the pathology developed in cardiomyocytes. This indicated that they were oxidized. Increased concentrations of primary lipid peroxidation products (diene conjugates), inhibition of aconitate hydratase activity, and accumulation of citrate were noted. Injection of Melaxen and Valdoxan to rats with EH normalized these parameters. The melatonin-correcting capability of the used drugs and the antioxidant activity of melatonin probably facilitated normalization of free-radical homeostasis in rat cardiomyocytes with the pathology.

The effect of melaxen administration on the tissue oxidative status in rats with brain ischemia/reperfusion

Melaxen administration to rats with brain ischemia/reperfusion was accompanied by a decrease of the lactate level (an organ ischemia marker), biochemiluminescence parameters characterizing the intensity of free radical processes and total antioxidant activity, the content of lipid peroxidation products, activity of superoxide dismutase and catalase, as compared with the values determined in rats with induced brain ischemia/reperfusion. Activity of aconitate hydratase, a sensitive target of free radicals action, and the citrate level in the brain and blood serum of melaxen-treated animals changed towards control values of intact animals. It is assumed that the effect of melaxen is associated with implementation of the antioxidant and protective properties of melatonin, the melaxen constituent, under conditions of post-ischemic reperfusion injury, accompanied by oxidative stress development.

Effects of Thioctic Acid on the Oxidative Status Tissues in Rheumatoid Arthritis in Rats

Biochemiluminescence, aconitate hydratase activity, and citrate contents were studied in rat serum and muscle in normal animals and in experimental rheumatoid arthritis; the actions of thioctic acid on the background of the development of this pathology were also studied. The development of rheumatoid arthritis in rats was accompanied by increases in marker values and measures of biochemiluminescence, as well as decreases in aconitate hydratase activity, evidently due to the extreme generation of reactive oxygen species associated with the induction of pathology. Suppression of the activity of this enzyme was linked with the accumulation of citrate in the tissues of the experimental rats. Administration of thioctic acid to rats with rheumatoid arthritis was accompanied by changes in values towards the normal, which was evidently linked with the antioxidant action of this compound.

Influence of 10-(6'-Plastoquinonyl)decyltriphenylphosphonium (SkQ1) on Oxidative Status in Rats with Protamine Sulfate-Induced Hyperglycemia.

An influence of 10-(6'-plastoquinonyl)decyltriphenylphosphonium (SkQ1) on oxidative status and activity of some antioxidant enzymes in the liver and blood serum from rats was examined during experimental hyperglycemia developed after injecting protamine sulfate. It was found that SkQ1 lowered glycemic level in rats treated with protamine sulfate. Moreover, it was also accompanied by restoration of the normal range of biochemiluminescence parameters indicating the rate of ongoing free radical processes, magnitude of primary products of lipid peroxidation such as diene conjugates, activity of aconitate hydratase, and level of citrate in rat liver and blood. Hence, it was demonstrated that activity of superoxide dismutase and catalase, increasing during hyperglycemia, was decreased after administering SkQ1. This might be related to the ability of SkQ1 to normalize free-radical homeostasis imbalanced during hyperglycemia.

Воздействие тиоктовой кислоты на оксидативный статус тканей крыс при ревматоидном артрите

Проведено исследование показателей биохемилюминесценции, активности аконитатгидратазы и содержания цитрата в сыворотке крови и мышцах крыс в норме, при экспериментальном ревматоидном артрите и действии тиоктовой кислоты на фоне развития патологии. Развитие ревматоидного артрита у крыс сопровождалось увеличением маркерных показателей и параметров биохемилюминесценции, а также снижением активности аконитатгидратазы, происходящим, по-видимому, вследствие чрезмерной генерации активных форм кислорода при индукции патологии. Угнетение активности данного фермента было сопряжено с накоплением цитрата в тканях крыс. Введение тиоктовой кислоты крысам с ревматоидным артритом сопровождалось изменением исследуемых параметров в сторону нормы, что, очевидно, было сопряжено с антиоксидантным действием данного соединения.

Effect of Succinic Acid and Chitosan Derivatives on Aconitate Hydratase Activity and Citrate Content in Rat Brain Tissues Under Ischemia/Reperfusion Conditions

Succinic-acid and chitosan derivatives administered at various dose to rats with brain ischemia/reperfusion led to a decrease in the level of lactate (an ischemia marker) in brain tissue as compared to the value in pathology. The activity of aconitate hydratase (a sensitive target of free-radical action) increased under these conditions whereas the citrate level in the brain and blood serum of the animals decreased toward the control values. The observed changes were dose-dependent. The results showed that these drugs were capable of reducing the degree of metabolic damage and the development of oxidative stress during post-ischemic reperfusion. Therefore, the investigated substances may be of considerable interest for pharmacological correction of metabolic changes during the development of such pathologies. Chitosan succinate exhibited more pronounced neuroprotective and antioxidant effects than N-succinylchitosan.

Effect of melaxen and valdoxan on free radical processes intensity, aconitate hydratase activity and citrate content in rats tissues under hyperthyroidism

The influence of melaxen and valdoxan on the biochemiluminescence parameters, aconitate hydratase activity and citrate level in rats heart and liver during development of experimental hyperthyroidism has been investigated. Administration of these substances promoted a decrease of biochemiluminescence parameters, which had been increased in tissues of rats in response to the development of oxidative stress under hyperthyroidism. Aconitate hydratase activity and citrate concentration in rats liver and heart, growing at pathological conditions, changed towards control value after administration of the drugs correcting melatonin level. The results indicate the positive effect of valdoxan and melaxen on oxidative status of the organism under the development of experimental hyperthyroidism that is associated with antioxidant action of melatonin.

The influence of N-[imino(1-piperidinyl)methyl]guanidine and N-[imino(4-morpholinyl)methyl]guanidine on citrate content, activities of aconitase and citrate synthase in rats exposed to cerebral ischemia-reperfusion

The effect of guanidine derivatives on citrate content and activity of aconitate hydratase and citrate synthase have been investigated in rats with cerebral ischemia-reperfusion. Administration of N-[imino(1-piperidinyl)methyl]guanidine and N-[imino(4-morpholinyl)methyl]guanidine resulted in changes of specific activities of aconitase and citrate synthase towards control values. Under these conditions the citrate level considerably decreased versus rats with untreated ishemia-reperfusion. Administration of these biguanidines compounds also decreased the degree of DNA fragmentation, which was markedly increased in rats with ischemia-reperfusion. The dose-dependent effects of guanidine derivatives suggest that they exhibit not only antioxidant but also prooxidant effects.

Effects of lipoic acid on citrate content, aconitate hydratase activity, and oxidative status during myocardial ischemia in rats

The effects of lipoic acid on intensity of free radical reactions, citrate content, and aconitate hydratase during myocardial ischemia have been investigated. Treatment with lipoic acid normalized biochemiluminescence parameters and citrate level, which were increased in the myocardial pathology. Treatment with lipoic acid also increased specific activity of aconitate hydratase, which was decreased in myocardium and blood of animals with myocardial ischemia. Administration of lipoic acid decreased DNA fragmentation observed during myocardial ischemia. The data suggest that lipoic acid can be effectively used as a cardioprotector preventing the development of free radical oxidation during myocardial ischemia.

Oxidative status and citrate concentration in rat tissues during experimental hyperthyroidism and melatonin treatment

Biochemiluminescence increased, while aconitate hydratase activity and citrate accumulation in tissues of the liver and heart and blood decreased in rats with experimental hyperthyroidism. These changes reflect activation of free radical oxidation, damage to enzyme molecules with reactive oxygen species, and impaired utilization of citrate under pathological conditions. Melatonin treatment during hyperthyroidism normalized aconitate hydratase activity and citrate concentration. Biochemiluminescence study showed that the effect of melatonin is related to antioxidant activity of this hormone, inhibition of free radical oxidation, and suppression of reactive oxygen species generation.