Effect of catalase-specific inhibitor 3-amino-1,2,4-triazole on yeast peroxisomal catalase in vivo

3-Amino-1,2,4-triazole (3-AT) is known as an inhibitor of catalase to whose active center it specifically and covalently binds. Subcellular fractionation and immunoelectronmicroscopic observation of the yeast Candida tropicalis revealed that, in 3-AT-treated cells in which the 3-AT was added to the n-alkane medium from the beginning of cultivation, catalase transported into peroxisomes was inactivated and was present as insoluble aggregated forms in the organelle. The aggregation of catalase in peroxisomes occurred only in these 3-AT-treated cells and not in cells in which 3-AT was added at the late exponential growth phase. Furthermore, 3-AT did not affect the transportation of catalase into peroxisomes. The appearance of aggregation only in cells to which 3-AT was added from the beginning of cultivation suggests that, in the process of catalase transportation into yeast peroxisomes, some conformational change may take place and that correct folding may be inhibited by the binding of 3-AT to the active center of catalase. Accordingly, 3-AT will be an interesting compound for investigation of the transport machinery of the peroxisomal tetrameric catalase.     

Effect of chronic ethanol, catalase inhibitor 3-amino-1,2,4-triazole and clofibrate treatment on lipid peroxidation in rat myocardium

1. The effect of chronic alcohol consumption, catalase inhibitor 3-amino-1,2,4-triazole (amino-triazole) and peroxisome proliferator clofibrate on the level of Fe/ADP-ascorbate-induced lipid peroxidation has been studied in the rat myocardium. The intensity of lipid peroxidation was measured using chemiluminescence technique and malondialdehyde formation. 2. Combined us well as separate treatment with ethanol (36% of dietary calories) and aminotriazole caused elevation of the rate of lipid peroxidation in the nuclear-free homogenate or total particulate fraction of the rat heart. The most pronounced effect was noted during combined application of ethanol and aminotriazole. 3. Prolonged clofibrate treatment significantly increased the level of nonenzymatic lipid peroxidation in the rat myocardium. 4. Peroxidative alteration of the myocardial lipids in vivo was evaluated by measurement of conjugated dienes (absorbance at 233 nm). Separate ethanol, aminotriazole or clofibrate treatment did not affect the level of u.v. absorption of lipids from the total particulate fraction. However, when ethanol and aminotriazole were administered simultaneously an increase of conjugated diene formation was observed. 5. The data obtained confirm the hypothesis that ethanol or clofibrate-induced activation of the myocardial lipid peroxidation may be due to the increase of hydrogen peroxide-generating capacity of the heart microperoxisomes.     

Reaction of 3-amino-1:2:4-triazole with lactoperoxidase

Bovine lactoperoxidase (LPO) gradually lost its enzymatic activity when dialyzed against a solution of 3-amino-1:2:4-triazole (AT) and hydrogen peroxide at pH 7.0. Amino acid analysis of the completely inactive enzyme revealed the formation of a new ninhydrin-positive chromatographic peak. This peak which had been observed previously when catalases were similarly reacted with AT in the presence of hydrogen peroxide is attributed to the covalent reaction product of AT with a histidyl residue. Concurrently with the appearance of the new ninhydrin-positive peak, the histidine content of LPO decreased by approximately two residues. Four to five residues of tyrosine were also lost.     

Features of the inhibition of catalase activity by 3-amino-1,2,4-triazole in erythrocytes and liver of rats with streptozotocin diabetes]

Lipid peroxidation was intensified by streptozotocin induced diabetes mellitus in erythrocytes and liver. Activity of antioxidant enzyme superoxide-dismutase was decreased, activity of catalase was increased. Concentration of lipid peroxidation products was decreased after nicotinamide injections. It was investigated liver- and erythrocyte catalase inhibition in the presence of 3-amino-1,2,4-triazole. Effective inhibitor concentration for liver catalase by streptozotocin induced diabetes mellitus was 10 mM, by control-20 mM. Ascorbic acid induced catalase inhibition in the erythrocytes by diabetes mellitus increased by ascorbic acid concentration from 25 to 150 mM. [DHAA]/[AA]-ratio increased from 0.26 by control to 1.6 by diabetes mellitus and decreased to 0.44 after nicotinamide injections.     

3-amino-1,2,4-triazole inhibits macrophage NO synthase.

Murine macrophages activated by interferon-gamma and lipopolysaccharide become leishmanicidal through a process involving L-arginine-derived nitrogen oxidation products. Both nitrite secretion and parasite killing by activated macrophages were inhibited by 3-amino-1,2,4-triazole as well as the related compound, 3-amino-1,2,4-triazine. Moreover, NO synthase activity in cytosolic extracts of activated cells was inhibited by both compounds. 4-amino-1,2,4-triazole, an isomer of 3-amino-1,2,4-triazole, was without effect. Our results suggest that besides its known inhibitory effect on catalases and peroxidases, 3-amino-1,2,4-triazole is an inhibitor of NO synthase. The resemblance between the tautomeric form of 3-amino-1,2,4-triazole and the guanidino group of L-arginine, the natural substrate for NO synthase, might be responsible for the observed inhibition.     

Determination of 3-amino-5-mercapto-1,2,4-triazole in serum

A high performance liquid chromatography (HPLC) method using fluorescence detection to determine 3-amino-5-mercapto-1,2,4-triazole (AMT) levels in serum has been developed. Sample preparation involved treatment with tributylphosphine (TBP) to reduce disulfides formed during storage, precipitation of proteins with acetonitrile (ACN), and precolumn derivatization using the thiol reactive fluorescent probe monobromobimane (MBB). The conjugate (AMT-MBB) was resolved by gradient elution from a C(18) reversed-phase column. The assay method was linear over a concentration range of 0.78-50 microg/ml and had a limit of detection (LOD) of 0.05 microg/ml AMT (10 microl injection). This method provides a sensitive and specific tool for the determination of AMT in serum and may have potential industrial hygiene application.     

Blockade of ethanol induced conditioned taste aversion by 3-amino-1,2,4-triazole: evidence for catalase mediated synthesis of acetaldehyde in rat brain

This investigation seeks to present evidence for the oxidation of ethanol in the brain via the peroxidatic activity of catalase and simultaneously provide evidence for the role of central acetaldehyde (ACH) in the mediation of an ethanol-induced conditioned taste aversion (CTA). Ethanol is capable of inducing a conditioned taste aversion. Pretreatment with the catalase inhibitor, 3-amino-1,2,4-triazole (AT), shows an attenuation of this ethanol-induced CTA. Animals receiving ethanol injections showed a CTA to a novel solution paired with a drug administration, while ethanol injected animals pretreated with AT did not show a CTA to ethanol administration. This effect of AT appears to be specific to the effects of ethanol as CTA's to morphine and lithium chloride were not affected by AT pretreatment. Peripheral levels of ethanol were the same in all animals regardless of pretreatment indicating that AT had no effect on peripheral levels of ethanol. These data increase support for the notion that acetaldehyde is produced directly in the brain and that it may be the agent mediating some of the psychopharmacological properties of ethanol.     

Regulation of hydrogen peroxide in eye humors effect of 3-amino-1H-1,2,4-triazole on catalase and glutathione peroxidase of rabbit eye

Activities of catalase (H₂O₂ : H₂O₂ oxidoreductase, EC 1.11.1.6) and GSH peroxidase (GSH : H₂O₂ oxidoreductase, EC 1.11.1.9) have been measured in iris, ciliary body, retina, corneal epithelium, corneal endothelium, lens capsule-epithelium and decapsulated lens. 3-Amino-1H-1,2,4-triazole is a specific inhibitor of catalase and a potent cataractogenic agent. We observed marked inhibition of catalase activity in these tissues 1–6 h after the administration of a single intravenous dose of 1 g 3-aminotriazole per kg body weight in rabbit. This was associated with a 2–3-fold increase in the H₂O₂ concentrations of aqueous humor and vitreous humor. The increased peroxide concentrations were restored to the physiological levels as the catalase activity of eye tissues gradually returned to normal with time after injection. Under the conditions, GSH peroxidase activity of the afore-mentioned eye tissues was unaltered, GSH and protein sulfhydryl of lens were not changed, and ascorbic acid of aqueous humor and vitreous humor was not significantly altered. Based on these findings our conclusion is that catalase of eye tissues regulates the endogenous H₂O₂ in eye humors to the physiological level. We speculate that H₂O₂ may be the triggering factor in cataract induced by 3-aminotriazole.