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PubMed1985

A comparison of two catalase preparations used to examine vascular permeability.

Beef liver catalase has been used as a tracer in cytochemical studies of vascular permeability. The use of Sigma catalase C-40 and C-100 preparations in capillary permeability studies of the ileojejunum and choriocapillaris was examined. Catalase C-40 is restricted by the fenestrated capillaries of the ileojejunum in contrast to their permeability to C-100. The choriocapillaris restricts both catalase preparations. Sephadex G-200 chromatography of plasma samples incubated with catalase C-40, or from C-40-injected animals, demonstrated an increase in the molecular weight of the tracer. No increase in molecular weight was evident for catalase C-100. The isoelectric point of both preparations was 5.4-5.7. These findings indicate that Sigma catalase C-100 is the preferred preparation for use in vascular permeability studies.

Animals↗
PubMed1992

Relationship between catalase activity, life span and some parameters associated with antioxidant defenses in Drosophila melanogaster.

This study was conducted on Drosophila melanogaster mutants with different levels of catalase activity in order to assess the role of antioxidant defenses in the aging process. We present here the analysis of two mutant strains: the catn1/catn4 heterozygote which exhibits no detectable catalase activity and the catn2 homozygote which exhibits approximately 14% that of the parent reference strain. Since insects lack glutathione peroxidase activity, catalase activity provides the sole enzymatic mechanism for the removal of H2O2. Average and maximum life spans of flies were unaffected by the absence or low levels of catalase activity. The mutants however exhibited adaptive responses in their metabolic rate or glutathione content. The metabolic rate of flies was significantly lowered in the null mutants. Glutathione concentration tended to increase in flies with the hypomorphic catalase allele (exhibiting 14% of the normal catalase activity). Gamma-glutamylcysteine synthetase activity was significantly higher in the null flies. Activities of superoxide dismutase and glutathione reductase were unaffected. Results of this study indicate that 14% of the normal level of catalase activity allows flies to achieve both a normal life span and a normal metabolic potential. Small decreases in certain antioxidant defenses, frequently observed during aging, may be functionally not very consequential.

Aging↗
PubMed1989

Catalase: its role in xenobiotic detoxification.

Catalase activity is found primarily in peroxisomes although in some species and in some organ systems, cytosolic catalase also may be involved in intracellular oxidant stress protection. Toxicology studies with repeat exposures to xenobiotics producing hydrogen peroxide either directly or indirectly generally indicate that the organisms develop resistance to the toxin (adaptation). This adaptation would result from induction of catalase activity in most target organs. The induction of hepatic peroxisomes accompanied by less than compensatory increase in catalase activity is now recognized as suggesting a potential for hepatotoxic and hepatocarcinogenic effects. Although these effects seem to also require mobilization of fatty acids, it is not clear if such mobilization is an absolute requirement. As would be expected, there are great differences among species in catalase activity thus making animal-human extrapolations difficult. Finally, with the exception of premature and neonatal animals, age-related variations in catalase activity do not seem to be large enough to have toxicological relevance. However, in old animals, their apparent inability to replace lost catalase activity after repeated stress may have major significance in explaining observed young-old differences in toxicity resulting from oxidant stress.

Aging↗
PubMed1988

Characterization of catalase transcripts and their differential expression in maize.

In maize, the three unlinked catalase (EC 1.11.1.6) structural genes (Cat1, Cat2 and Cat3) are differentially expressed temporally, spatially and in response to environmental signals in the developing seedling. In order to understand more fully the molecular mechanisms involved in catalase gene expression, full-length cDNA clones representing the maize Cat1, Cat2 and Cat3 transcripts were isolated and characterized. DNA sequence analysis confirmed that each cDNA encodes a unique catalase protein. Gene-specific probes for the three maize catalase cDNAs were isolated and used to probe blots of poly(A)+ RNA isolated from various maize tissues. Cat1 mRNA was found in scutella, milky endosperm of immature kernels, leaves and epicotyls. The Cat2 mRNA was present primarily in post-germinative scutella, with lower levels in leaves and epicotyls. Cat3 mRNA was detected primarily in epicotyls and, to a lesser extent, in leaves and scutella. The gene-specific probes hybridized with maize genomic DNA blots in simple, but unique patterns, indicating that there is one, or a very few copies of each catalase gene. The coding region of the Cat3 cDNA comprised 66% G + C, which led to a strong codon usage bias in this gene. This codon bias was also seen with the Cat2 transcripts, but not with those for Cat1. A high degree of similarity was found between the maize catalase nucleic acid and deduced amino-acid sequences and those of sweet potato and rat liver catalase.

Amino Acid Sequence↗
PubMed1990

Inhibition of catalase and epoxide hydrolase by the renal cystogen 2-amino-4,5-diphenylthiazole and its metabolites.

Subchronic feeding of 2-amino-4,5-diphenylthiazole (DPT) to rats results in the development of renal cysts and has been used as a model system to study polycystic kidney disease. Because previous studies revealed changes in renal enzymes following DPT administration, a possible direct effect of DPT and its phenolic metabolites on catalase and a related enzyme, epoxide hydrolase, was examined. Experiments with three in vitro systems (suspensions of rabbit renal tubules, rat kidney homogenates, and commercially obtained bovine liver catalase) revealed direct inhibition of catalase activity by the diphenolic metabolite (diOH- DPT: 2-amino-4,5di(4'-hydroxyphenyl)-thiazole), the known renal cystogen nordihydroquaiaretic acid (NDGA) 2-amino-4(4'-hydroxyphenyl),5-phenyl-thiazole (4OH-DPT), and the known catalase inhibitor 3-amino-1,2,4-triazole; DPT did not inhibit catalase activity. Following oral administration to rats of the DPT congeners, 4OH-DPT caused the greatest decrease in both renal catalase and cytosolic epoxide hydrolase activities and the shortest time to onset of cystic lesions. In vitro, mouse liver cytosolic epoxide hydrolase activity was substantially inhibited by 4OH-DPT and dioH-DPT, and NDGA, but not by 2-amino-4-phenyl,5-(4'-hydroxyphenyl)-thiazole (5OH-DPT) or DPT itself. Microsomal epoxide hydrolase (mEH) activity was inhibited by 4OH-DPT, unaffected by DPT or dioH-DPT, and stimulated 2-fold by 5OH-DPT. Finally, mEH activity was substantially higher in samples of normal human kidney than in samples of kidney derived from a patient with autosomal recessive polycystic kidney disease; no differences were observed in cEH activity in these samples. Although the role of altered catalase and epoxide hydrolase activities in cystogenesis is unknown, DPT-induced cyst formation is associated with loss of these enzyme activities in kidney tissue. To our knowledge, this is the first report of an in vivo diminution of cytosolic epoxide hydrolase activity by xenobiotics.

8,11,14-Eicosatrienoic Acid↗
PubMedDate not supplied

A correlation between voluntary ethanol consumption and brain catalase activity in the rat.

The relationship between voluntary ethanol consumption and brain catalase activity was investigated in male Long Evans rats. In the first study, rats which were voluntarily consuming alcohol or water for 25 days were sacrificed by decapitation immediately (group A) or 15 days (group B) following withdrawal of alcohol and their brains analysed for catalase activity. Mean brain catalase activity did not differ among the two groups of rats exposed to ethanol and the ones exposed to water only. Furthermore, there were significant positive correlations between individual voluntary ethanol intake and catalase activity in both groups, (group A:r = .69, p less than or equal to 0.05; group B:r = .54, p less than or equal to 0.05). In the second study, rats were forced to drink high levels of ethanol presented as the only source of fluid for 25 days. Rats were sacrificed and brain, liver, muscle and heart tissue were extracted and analysed for catalase activity. There were no differences in mean brain catalase activity between water and forced ethanol drinking rats indicating that the enzyme was not inducible by high volume ethanol consumption. The results suggest that inherent differences in brain catalase activity may be one of the factors in determining an animal's propensity to voluntarily consume ethanol.

Acetaldehyde↗
PubMed1993

Roles of catalase and cytochrome c in hydroperoxide-dependent lipid peroxidation and chemiluminescence in rat heart and kidney mitochondria.

A recent report (Radi et al., J. Biol. Chem. 266:22028-22034, 1991) showed that rat heart mitochondria contain catalase. The protective role of mitochondrial catalase was tested by exposing heart or kidney mitochondria and mitoplasts to two oxidants (H2O2) or tert-butyl hydroperoxide, t-BOOH), estimating lipid peroxidation (as thiobarbituric acid-reactive substances, TBARS) and overall oxidative stress (as chemiluminescence). Additional controls included heart and kidney preparations from aminotriazole-treated (catalase-depleted) rats. Both oxidants increased TBARS in catalase-free preparations to similar extents over their respective controls (between 200 to 350%). In catalase-containing preparations, H2O2 lipid peroxidation increased by only 40 to 96% over controls. Similar qualitative results were obtained when measuring chemiluminescence. The catalytic role of cytochrome c in mitochondrial lipid peroxidation was investigated by exposing either control or cytochrome-c-depleted kidney mitoplasts (catalase free) to either H2O2 or t-BOOH. Hydrogen-peroxide-dependent mitochondrial lipid peroxidation varied with cytochrome c concentration, remaining close to controls when cytochrome c concentration decreased by 66%, even though there was no catalase present. Tert-butyl hydroperoxide-dependent lipid peroxidation was less affected by cytochrome c remaining 2.3-fold above controls under the same conditions, suggesting that organic peroxides are more likely to remain in the less polar membrane environment being decomposed by heme or nonheme iron imbedded in the inner mitochondrial membrane. Chemiluminescence was less affected by cytochrome c depletion. Comparing control and cytochrome-c-deficient mitochondria, chemiluminescence was 1.7-fold and 2.8-fold higher when control preparations were challenged with t-BOOH or H2O2, respectively.

Animals↗
PubMed2004

Spectrophotometric analysis of the protective effect of ascorbate against spontaneous oxidation of tetrahydrobiopterin in aqueous solution: kinetic characteristics and potentiation by catalase of ascorbate action.

Tetrahydrobiopterin (BH(4)) is oxidized by O(2) readily in aqueous solutions and physiological concentrations of ascorbate have been shown to inhibit this reaction. In order to gain insight into the mechanism of ascorbate effect, a spectrophotometric analysis was applied for the study of the time course of BH(4) oxidation in the presence of various concentrations of ascorbate and the effect of various temperatures on the apparent second-order rate constant of BH(4) oxidation (k(ox)) in the presence or absence of catalase. In 100 micromol/l concentration, ascorbate alone prolonged the half-life time of 36 micromol/l BH(4) 1.4-fold whereas in the presence of catalase 1.85-fold. In the presence of catalase ascorbate decreased the value of k(ox) to 51 +/- 0.67%, whereas in the absence of it only to 64 +/- 0.77% of control (P < 0.01). The extent of ascorbate effect was not dependent on temperature, at least between 22 and 37 degrees C, either in the presence or absence of catalase. In the absence of catalase the apparent Arrhenius activation energies: 57.02 +/- 0.09 kJ/mol (-ascorbate) and 56.77 +/- 2.21 kJ/mol (+ascorbate) whereas in the presence of catalase: 62.72 +/- 1.37 kJ/mol (-ascorbate) and 59.93 +/- 2.84 kJ/mol (+ascorbate, mean +/- S.E.M., n=3) were obtained. The study shows that catalase potentiates the BH(4)-stabilizing effect of ascorbate. It is concluded that removal of H(2)O(2) generated from BH(4) during oxidation by O(2) prevents a decrease of ascorbate concentration, and in the presence of ascorbate the pacemaker step in the overall reaction is the oxidation of BH(4) and not the reduction of the quinonoid BH(2) back to BH(4) by ascorbate.

Antioxidants↗
PubMed2006

Direct electrochemistry and electrocatalytic activity of catalase immobilized onto electrodeposited nano-scale islands of nickel oxide.

Cyclic voltammetry was used for simultaneous formation and immobilization of nickel oxide nano-scale islands and catalase on glassy carbon electrode. Electrodeposited nickel oxide may be a promising material for enzyme immobilization owing to its high biocompatibility and large surface. The catalase films assembled on nickel oxide exhibited a pair of well defined, stable and nearly reversible CV peaks at about -0.05 V vs. SCE at pH 7, characteristic of the heme Fe (III)/Fe (II) redox couple. The formal potential of catalase in nickel oxide film were linearly varied in the range 1-12 with slope of 58.426 mV/pH, indicating that the electron transfer is accompanied by single proton transportation. The electron transfer between catalase and electrode surface, (k(s)) of 3.7(+/-0.1) s(-1) was greatly facilitated in the microenvironment of nickel oxide film. The electrocatalytic reduction of hydrogen peroxide at glassy carbon electrode modified with nickel oxide nano-scale islands and catalase enzyme has been studied. The embedded catalase in NiO nanoparticles showed excellent electrocatalytic activity toward hydrogen peroxide reduction. Also the modified rotating disk electrode shows good analytical performance for amperometric determination of hydrogen peroxide. The resultant catalase/nickel oxide modified glassy carbon electrodes exhibited fast amperometric response (within 2 s) to hydrogen peroxide reduction (with a linear range from 1 microM to 1 mM), excellent stability, long term life and good reproducibility. The apparent Michaelis-Menten constant is calculated to be 0.96(+/-0.05)mM, which shows a large catalytic activity of catalase in the nickel oxide film toward hydrogen peroxide. The excellent electrochemical reversibility of redox couple, high stability, technical simplicity, lake of need for mediators and short preparations times are advantages of this electrode. Finally the activity of biosensor for nitrite reduction was also investigated.

Biosensing Techniques↗
PubMed2005

Catalase inhibition by amino triazole induces oxidative stress in goldfish brain.

The effects of in vivo inhibition of catalase by 3-amino 1,2,4-triazole (AMT) on the levels of damage products resulting from reactive oxygen species attack on proteins and lipids as well as on the activities of five antioxidant and associated enzymes were studied in the brain of goldfish, Carassius auratus. Intraperitoneal injection of AMT at a concentration of 0.1 mg/g wet weight caused a gradual decrease in brain catalase activity over 72 h, whereas higher AMT concentrations (0.5 or 1.0 mg/g) reduced catalase activity by about two-thirds within 5-10 h. AMT effects on antioxidant enzyme activities and oxidative stress markers were studied in detail using fish treated with 0.5 mg/g AMT for 24 or 168 h. The levels of thiobarbituric acid-reactive substances (a lipid damage product) increased 6.5-fold by 24 h after AMT injection but fell again after 168 h. The content of carbonylproteins (CP) also rose within 24 h (by approximately 2-fold) and remained 1.5-fold higher compared with respective sham-injected fish after 168 h. CP levels correlated inversely with catalase activity (R(2) = 0.83) suggesting that catalase may protect proteins in vivo against oxidative modification. The activities of both glutathione peroxidase and glutathione-S-transferase increased by approximately 50% and 80%, respectively, in brain of AMT-treated fish and this might represent a compensatory response to lowered catalase activity. Possible functions of catalase in the maintenance of prooxidant/antioxidant balance in goldfish brain are discussed.

Alcohol Oxidoreductases↗
PubMed2004

Catalase from the white shrimp Penaeus (Litopenaeus) vannamei: molecular cloning and protein detection.

Catalase is an antioxidant enzyme that plays a very important role in the protection against oxidative damage by breaking down hydrogen peroxide. It is a very highly conserved enzyme that has been identified from numerous species including bacteria, fungi, plants and animals, but the information about catalase in crustaceans is very limited. A cDNA containing the complete coding sequence for catalase from the shrimp Penaeus (Litopenaeus) vannamei was sequenced and the mRNA was detected by RT-PCR in selected tissues. Catalase was detected in hepatopancreas crude extracts by Western blot analysis with anti-human catalase polyclonal antibodies. The nucleotide sequence is 1692 bp long, including a 72-bp 5'-UTR, a coding sequence of 1515 bp and a 104-bp 3'-UTR. The deduced amino acid sequence corresponds to 505 amino acids with high identity to invertebrate, vertebrate and even bacterial catalases and contains the catalytic residues His71, Asn144, and Tyr354. The predicted protein has a calculated molecular mass of 57 kDa; which coincides with the size of the subunit (approximately 55 kDa) and the tetrameric protein (approximately 230 kDa) detected in hepatopancreas extracts under native conditions. Catalase mRNA level was higher in hepatopancreas, followed by gills and was not detected in muscle.

3' Untranslated Regions↗
PubMed2004

SHP2 binds catalase and acquires a hydrogen peroxide-resistant phosphatase activity via integrin-signaling.

Here, we examined whether catalase binds SHP2 and alters SHP2 susceptibility to H2O2. Our results indicated that serum and fibrinogen commonly evoked catalase binding to SHP2 in HeLa and A549 cells in a herbimycin-A and TNFalpha sensitive manner. Expression of active catalase nearly 15-fold over control levels in tet-off HeLa cells substantially increased the SHP2 binding, and the catalase-associated SHP2 displayed significantly high phosphatase activities with a H2O2-resistance compared to those with little catalase. Site-directed mutagenesis at 280 abolished the binding capability of catalase to SHP2-SH2 in vitro. These results suggest that catalase-280pYIQV binds SHP2 via integrin-signaling to increase a H2O2-resistant SHP2 activity.

Benzoquinones↗
PubMed2006

Catalase characterization and implication in bleaching of a symbiotic sea anemone.

Symbiotic cnidarians are marine invertebrates harboring photosynthesizing microalgae (named zooxanthellae), which produce great amounts of oxygen and free radicals upon illumination. Studying antioxidative balance is then crucial to understanding how symbiotic cnidarians cope with ROS production. In particular, it is suspected that oxidative stress triggers cnidarian bleaching, i.e., the expulsion of zooxanthellae from the animal host, responsible for symbiotic cnidarian mass mortality worldwide. This study therefore investigates catalase antioxidant enzymes and their role in bleaching of the temperate symbiotic sea anemone Anemonia viridis. Using specific separation of animal tissues (ectoderm and endoderm) from the symbionts (zooxanthellae), spectrophotometric assays and native PAGE revealed both tissue-specific and activity pattern distribution of two catalase electrophoretypes, E1 and E2. E1, expressed in all three tissues, presents high sensitivity to the catalase inhibitor aminotriazole (ATZ) and elevated temperatures. The ectodermal E1 form is responsible for 67% of total catalase activity. The E2 form, expressed only within zooxanthellae and their host endodermal cells, displays low sensitivity to ATZ and relative thermostability. We further cloned an ectodermal catalase, which shares 68% identity with mammalian monofunctional catalases. Last, 6 days of exposure of whole sea anemones to ATZ (0.5 mM) led to effective catalase inhibition and initiated symbiont expulsion. This demonstrates the crucial role of this enzyme in cnidarian bleaching, a phenomenon responsible for worldwide climate-change-induced mass mortalities, with catastrophic consequences for marine biodiversity.

Amino Acid Sequence↗
PubMed2004

Expression of the catalase gene katA in starter culture Lactobacillus plantarum TISTR850 tolerates oxidative stress and reduces lipid oxidation in fermented meat product.

The catalase gene katA of Lactobacillus sakei SR911 was cloned and expressed in Escherichia coli UM2 and Lactobacillus plantarum TISTR850 under strong lactococcal promoter P59 in E. coli-lactococcus expression vector pIL1020. The L. plantarum TISTR850 is a catalase-deficient strain isolated from local fermented meat product. The recombinant L. plantarum TISTR850 was shown to decompose hydrogen peroxide, and catalase activity approximately three times higher that of natural catalase-producing strain L. sakei SR911. The recombinant protein was also detected by in situ activity staining of the catalase enzyme. The recombinant L. plantarum TISTR850 did not accumulate hydrogen peroxide under glucose-limited aerobic conditions and remained viable after 60 h of incubation. The recombinant and host strain L. plantarum TISTR850 were used as starter cultures in the fermented meat product, and lipid oxidation was monitored over a 7-day storage at 20 degrees C determined as thiobarbituric acid-reactive substances (TBARS) value. The lipid oxidation level in the fermented meat product seeded with the catalase genetically modified starter culture L. plantarum TISTR850 was significantly lower than that of the natural catalase-deficient strain.

Catalase↗
PubMed2005

Cocaine alters catalase activity in prefrontal cortex and striatum of mice.

Catalase is one of the enzymes that convert hydrogen peroxide (H2O2) to H2O presenting a protective role against free radicals. In this study, catalase activity was determined in homogenates of striatum (ST) and prefrontal cortex (PFC) in order to examine the participation of oxidative stress (OS) on cocaine actions in mice brain. Male Swiss mice were injected (i.p.) with cocaine at low (10 and 30 mg/kg) and high doses (90 mg/kg), and observed for 1 h. After cocaine overdose (90 mg/kg) some animals presented only status epilepticus (SE) while others died after seizures. These animals were dissected and divided in two groups, SE and death. Catalase activity was also determined after pretreatment with the anticonvulsant drug, diazepam, alone or injected before cocaine 90 mg/kg, and after seizures induced by a high dose of bupropion, a known inhibitor of NE and DA reuptake used for comparison. Results showed a decrease in catalase activity of the PFC and ST after SE and death induced by cocaine and bupropion overdoses. Cocaine at low doses decreased the enzyme activity only in ST. Diazepam treatment alone and before cocaine overdose did not interfere with catalase activity. This reduction in catalase activity may reflect an increase in H2O2 content in PFC and ST. Previous data reports that H2O2 inhibits dopamine transporter activity, suggesting that the decrease in catalase activity may potentiate the toxic mechanism of drugs that inhibit monoamines reuptake. As far as we know, this is the first report showing an involvement of OS in the cocaine's central mechanism of action.

Adrenergic Uptake Inhibitors↗
PubMed2006

Acute administration of 3-nitropropionic acid, a reactive oxygen species generator, boosts ethanol-induced locomotor stimulation. New support for the role of brain catalase in the behavioural effects of ethanol.

The antioxidant enzyme catalase by reacting with H(2)O(2), forms the compound known as compound I (catalase-H(2)O(2)). This compound is able to oxidise ethanol to acetaldehyde in the CNS. It has been demonstrated that 3-nitropropionic acid (3-NPA) induces the activity of the brain catalase-H(2)O(2) system. In this study, we tested the effect of 3-NPA on both the brain catalase-H(2)O(2) system and on the acute locomotor effect of ethanol. To find the optimal interval for the 3-NPA-ethanol interaction mice were treated with 3-NPA 0, 45, 90 and 135min before an ethanol injection (2.4mg/kg). In a second study, 3-NPA (0, 15, 30 or 45mg/kg) was administered SC to animals 90min before saline or several doses of ethanol (1.6 or 2.4g/kg), and the open-field behaviour was registered. The specificity of the effect of 3-NPA (45mg/kg) was evaluated on caffeine (10mg/kg IP) and cocaine (4mg/kg)-induced locomotion. The prevention of 3-NPA effects on both ethanol-induced locomotion and brain catalase activity by L-carnitine, a potent antioxidant, was also studied. Nitropropionic acid boosted ethanol-induced locomotion and brain catalase activity after 90min. The effect of 3-NPA was prevented by l-carnitine administration. These results indicate that 3-NPA enhanced ethanol-induced locomotion by increasing the activity of the brain catalase system.

Acetaldehyde↗
PubMed2004

Significant contamination of superoxide dismutases and catalases with lipopolysaccharide-like substances.

Commercially available superoxide dismutase (SOD) and catalase induced remarkable morphological changes in cultured peritoneal resident macrophages (PRMs). The morphology resembled that of cells stimulated with various macrophage-activating substances such as bacterial lipopolysaccharides (LPS). PRMs treated with SOD and catalase for 24 h produced a significant amount of nitric oxide. Peritoneal thioglycollate-exudated macrophages (PEMs) that were induced to die by combined treatment with LPS and cycloheximide (protein synthesis inhibitor) were killed by the treatment with SOD and catalase in the presence of cycloheximide. The effect of SOD and catalase was heat-resistant and was not found in PEMs of the C3H/HeJ mouse, an LPS low responder strain. These results strongly indicated the presence of LPS-like substances in the sample of SOD and catalase used. An examination of commercially available SOD and catalase samples for the presence of LPS-like substances demonstrated that many were contaminated. The LPS contamination was directly confirmed by bacterial endotixins test. It is quite important to take into consideration that commercially available SODs and catalases may be contaminated with LPS and the contaminants may affect the results of studies.

Animals↗
PubMed2003

Bio-effectiveness of Tat-catalase conjugate: a potential tool for the identification of H2O2-dependent cellular signal transduction pathways.

Reactive oxygen species such as hydrogen peroxide (H(2)O(2)) have taken center stage as bona fide second messengers in various signaling pathways. Here, we report the synthesis, metabolic fate, and effectiveness in modulating such pathways of a Tat-catalase conjugate. Incubation of L2 cells with Tat-catalase greatly increased cell-associated enzymatic activity, reaching close to a plateau by 30 min. The cell-associated catalase activity and antibody-detectable Tat-derivatives declined over time after changing medium, although still remaining at significantly higher levels than baseline even at 4h. While most cell-associated Tat-catalase was apparently tightly attached to the cell surface, a small fraction entered the cells as the proteasome inhibitor MG-132 slightly prevented the disappearance of the enzyme. Tat-catalase, either membrane-bound or intracellular, but not native catalase, inhibited serum-induced Elk phosphorylation and anisomycin- and/or MG-132-induced ERK phosphorylation, suggesting the involvement of H(2)O(2). Thus, Tat-catalase should be a useful tool to dissect H(2)O(2)-dependent events in signaling pathways.

Animals↗