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PubMed1988

Catalase in guinea pig hepatocytes is localized in cytoplasm, nuclear matrix and peroxisomes.

We have compared the intracellular localization of catalase and another peroxisomal marker enzyme, alpha-hydroxy acid oxidase (HAOX), in the livers of guinea pig and rat using immunoelectron microscopy and subcellular fractionation combined with immunoblotting and enzyme activity determination. Antibodies against both enzymes were raised in rabbits and their specificities established by immunoblotting. By immunoelectron microscopy, gold particles representing antigenic sites for catalase were found in guinea pig hepatocytes not only in peroxisomes but also in the cytoplasm and the nuclear matrix. In rat liver, however, catalase was localized exclusively in peroxisomes with no cytoplasmic labeling. Moreover, in both species HAOX was found only in peroxisomes. Subcellular fractionation revealed that purified peroxisomes from both species contained comparable levels of each, catalase and HAOX activities. The total catalase activity, however, was substantially higher in guinea pig and most of this excess catalase was in the cytosolic fraction with some activity also in nuclei. In rat liver, 30 to 40% of both enzymes and in guinea pig liver 30% of HAOX were recovered in the supernatant fraction implying that the fragility of peroxisomes in both species is quite comparable. These observations establish the occurrence of extraperoxisomal catalase in guinea pig liver. The catalase in the cytoplasm and nucleus of liver parenchymal cells is most probably involved in scavenging of H2O2, protecting the cell against toxic and mutagenic effects of this noxious agent.

Animals↗
PubMed1996

Active involvement of catalase during hemolytic crises of favism.

The endemic occurrence of favism in certain Mediterranean regions provided an investigative opportunity for testing in vivo the validity of claims as to the role of catalase in protecting human erythrocytes against peroxidative injury. Reduced activity of catalase was found in the erythrocytes of six boys who were deficient in erythrocytic glucose-6-phosphate dehydrogenase (G6PD) and who were studied while suffering hemolysis after ingesting fava beans. Activity of catalase was further reduced when their red blood cells were incubated with aminotriazole. In contrast, minimal reduction of catalase activity was found, both with and without incubation with aminotriazole, in erythrocytes of a G6PD-deficient boy who had ingested fava beans 7 days earlier and in erythrocytes of seven G6PD-deficient men with a past history of favism. These results confirmed earlier studies in vitro indicating that catalase is a major disposer of hydrogen peroxide in human erythrocytes and, like the glutathione peroxidase/reductase pathway, is dependent on the availability of reduced nicotinamide adenine dinucleotide phosphate (NADPH). The effect of divicine on purified catalase and on the catalase of intact G6PD-deficient erythrocytes was similar to the previously demonstrated effect on catalase of a known system for generating hydrogen peroxide. This effect of divicine strengthens earlier arguments that divicine is the toxic peroxidative component of fava beans.

Catalase↗
PubMed1996

[Catalytic properties of catalase in microemulsions of surface-active agents in octane].

The rate constants of H2O2 decomposition, interaction of catalase complex I with H2O2, and the effective rate constants of catalase inactivation during enzymatic catalysis (k(in)) were determined by transformation of complete kinetic curves of H2O2 decomposition by catalase in reversed micelles of Aerosol OT (AOT) in octane and aqueous solution. Effects of hydration of micelles and AOT, H2O2, and catalase concentrations in the micellar systems on each of three kinetic constants were investigated. Optimal conditions were found which provide for high operational stability and catalytic activity of catalase in micellar systems versus aqueous solutions. Stability of catalase enhances (decreased k(in)) in the presence of reduced glutathione and ethanol in AOT micelles. In reversed AOT micelles, catalase partially dissociates to subunits because their peroxidase activity was demonstrable in cumene hydroperoxide-dependent oxidation of tetramethylbenzidine. Catalase dissociation to monomers is significantly decreased in mixed micelles composed of AOT, Triton X-45, Triton X-100, or Tween-85 and octanol.

Catalase↗
PubMed1998

Role of catalase in in vitro acetaldehyde formation by human colonic contents.

Ingested ethanol is transported to the colon via blood circulation, and intracolonic ethanol levels are equal to those of the blood ethanol levels. In the large intestine, ethanol is oxidized by colonic bacteria, and this can lead to extraordinarily high acetaldehyde levels that might be responsible, in part, for ethanol-associated carcinogenicity and gastrointestinal symptoms. It is believed that bacterial acetaldehyde formation is mediated via microbial alcohol dehydrogenases (ADHs). However, almost all cytochrome-containing aerobic and facultative anaerobic bacteria possess catalase activity, and catalase can, in the presence of hydrogen peroxide (H2O2), use several alcohols (e.g., ethanol) as substrates and convert them to their corresponding aldehydes. In this study we demonstrate acetaldehyde production from ethanol in vitro by colonic contents in a reaction catalyzed by both bacterial ADH and catalase. The amount of acetaldehyde produced by the human colonic contents was proportional to the ethanol concentration, the amount of colonic contents, and the length of incubation time, even in the absence of added nicotinamide adenine dinucleotide or H2O2. The catalase inhibitors sodium azide and 3-amino-1,2,4-triazole (3-AT) markedly reduced the amount of acetaldehyde produced from 22 mM ethanol in a concentration dependent manner compared with the control samples (0.1 mM sodium azide to 73% and 10 mM 3-AT to 67% of control). H2O2 generating system [beta-D(+)-glucose + glucose oxidase] and nicotinamide adenine dinucleotide induced acetaldehyde formation up to 6- and 5-fold, respectively, and together these increased acetaldehyde formation up to 11-fold. The mean supernatant catalase activity was 0.53+/-0.1 micromol/min/mg protein after the addition of 10 mM H2O2, and there was a significant (p < 0.05) correlation between catalase activity and acetaldehyde production after the addition of the hydrogen peroxide generating system. Our results demonstrate that colonic contents possess catalase activity, which probably is of bacterial origin, and indicate that in addition to ADH, part of the acetaldehyde produced in the large intestine during ethanol metabolism can be catalase dependent.

Acetaldehyde↗
PubMed1996

The catalase-peroxidase of Synechococcus PCC 7942: purification, nucleotide sequence analysis and expression in Escherichia coli.

Synechococcus PCC 7942, a cyanobacterium, possesses catalaseperoxidase as the sole hydrogen peroxide-scavenging system. The enzyme has been purified to electrophoretic homogenenity from the cells. The native enzyme had a molecular mass of 150 kDa and was composed of two identical subunits of molecular mass 79 kDa. The apparent Km value of the catalase activity for H2O2 was 4.2 +/- 0.27 mM and the kcat value was 2.6 x 10(4) s-1. The enzyme contained high catalase activity and an appreciable peroxidase activity with o-dianisidine and pyrogallol. The catalase activity was not inhibited by 3-amino-1,2,4-triazole but by KCN and NaN3 (apparent Ki values 19.3 +/- 0.84 and 20.2 +/- 0.95 microM respectively). The enzyme showed an absorption spectrum of typical protohaem and contained one protohaem molecule per dimer. The gene encoding catalase-peroxidase was cloned from the chromosomal DNA of Synechococcus PCC 7942. A 2160 bp open reading frame (ORF), coding a catalase-peroxidase of 720 amino acid residues (approx. 79.9 kDa), was observed. The deduced amino acid sequence coincided with that of the N-terminus of the purified enzyme and showed a remarkable similarity to those of a family of catalase-peroxidases of prokaryotic cells. Escherichia coli BL21 (DE3)plysS, harbouring a recombinant plasmid containing the catalase-peroxidase gene, produced a large amount of proteins that co-migrated on SDS/PAGE with the native enzyme. The recombinant enzyme showed the same ratio of catalase activity to peroxidase activity with o-dianisidine and the same Km for H2O2 as the native enzyme.

Amino Acid Sequence↗
PubMed1989

Differential expression of the maize catalase genes during kernel development: the role of steady-state mRNA levels.

In maize three isozymic forms of catalase, CAT-1, CAT-2, and CAT-3 are encoded by three distinct and unliked structural genes (Cat1, Cat2 and Cat3). Catalase activity profiles and zymogram analysis were used to examine the spatial and temporal expression of the three genes during kernel maturation. Three developmental stages of catalase expression were observed in the growing kernel. During stage 1 (6-12 days after pollination), both Cat1 and Cat3 were expressed; during stage 2 (15-18 days after pollination) only Cat1 expression was observed; and during stage 3 (21-30 days after pollination), Cat1 and Cat2 were expressed. The major constituent tissues of the kernel were examined to determine their contribution to total kernel catalase expression. Each of the tissues was found to have a unique pattern of catalase gene expression. RNA blot analysis, using catalase gene-specific nucleic acid probes, suggests that the differential expression of the three catalase genes observed in the kernel is regulated by controlling the distribution of steady-state mRNA species for the three genes.

Blotting, Northern↗
PubMed1989

Characterization of human residual catalase of an acatalasemic patient by isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by electrophoretic blotting and immunodetection.

Isoelectric points and subunit sizes of catalases in human blood and human cultured skin fibroblasts from acatalasemic and normal subjects were analyzed by isoelectric focusing in agarose gel and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively, followed by electroblotting to polyvinylidene difluoride membranes for immunodetection. The results indicated that the isoelectric point of residual catalase in the C fraction prepared from acatalasemic erythrocytes was identical with that of catalase prepared from normal erythrocytes. The residual catalase in homogenates of acatalasemic cultured skin fibroblasts also reacted with anticatalase rabbit serum and had an isoelectric point identical with that of normal catalase. Subunit sizes of normal and acatalasemic catalases in the C fractions of erythrocytes were also found to be identical on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by electroblotting and immunoenzymatic amplification. The results indicated no substantial difference in molecular size and charge of catalase proteins between normal and acatalasemic erythrocytes and fibroblasts.

Acatalasia↗
PubMed1990

Characterization of human catalase by isoelectric focusing in presence of urea.

Human catalase from erythrocytes and liver were analyzed by polyacrylamide gel isoelectric focusing in presence and absence of urea using two different pH gradients, namely pH 6-8 and pH 6.7-7.7. In presence of urea, human catalase focused in the pH range 6.75-7.0, slightly anodal to that of hemoglobin A. In narrow pH gradients, human erythrocyte catalase was microheterogeneous. Neuraminidase from different sources and peptide-N-glycosidase F were applied to investigate the presence of sialic acid and/or carbohydrate chains in human catalase. A shift in the focusing pattern of both erythrocyte and liver catalase towards the anode was observed after treatment with one of the commercially available neuroaminidase preparations. This unusual result could be related to a contaminating protease since no effect was observed when the catalases were treated in presence of a serine protease inhibitor. In contrast, bovine liver and Macaca erythrocyte catalase did not display any detectable change in their focusing patterns after treatment with any of the neuraminidase preparations.

Catalase↗
PubMed2006

24,25-dihydroxyvitamin D3 binds to catalase.

There is increasing evidence that the vitamin D metabolite, 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) has endocrine actions. In the current work, we report that an endogenous binding protein for 24,25(OH)2D3 is catalase, based on sequence analysis of the isolated protein. An antibody (Ab 365) generated against equivalent protein recognized bovine catalase and a 64 kDa band in subcellular fractions of chick intestine. A commercially available anti-catalase antibody reduced specific [3H]24,25(OH)2D3 binding in subcellular fractions of chick intestine by greater than 65%, relative to the same fractions treated with an unrelated antibody (Ab 099). The same commercially available anti-catalase was able to block the inhibitory actions of 24,25(OH)2D3 on 32P uptake in isolated intestinal epithelial cell suspensions. We subsequently characterized binding of steroid to commercially available catalase, and found that between 0 and 5 nM of enzyme added to subcellular fraction P2 (20,000g, 10-min post-nuclear pellet) resulted in a linear increase in the amount of [3H]24,25(OH)2D3 specifically bound. Additional studies indicated that 25(OH)D3 was an effective competitor for binding, whereas 1,25(OH)2D3 only poorly displaced [3H]24,25(OH)2D3. Saturation analyses with added catalase yielded a physiologically relevant affinity constant (KD=5.6+/-2.7 nM) and a Bmax=209+/-34 fmols/mg protein, comparable to previous studies using purified basal lateral membranes or vesicular fractions. Moreover, in a study on subcellular fractions isolated from chickens of varying ages, we found that in females, both specific [3H]24,25(OH)2D3 binding and catalase activity increased from 7- to 58-week-old birds, whereas in males, elevated levels of both parameters were expressed in preparations of 7- and 58-week-old birds. The data suggest that signal transduction may occur through modulation of hydrogen peroxide production.

24,25-Dihydroxyvitamin D 3↗
PubMed2003

Structure of the Clade 1 catalase, CatF of Pseudomonas syringae, at 1.8 A resolution.

Catalase CatF of Pseudomonas syringae has been identified phylogenetically as a clade 1 catalase, closely related to plant catalases, a group from which no structure has been determined. The structure of CatF has been refined at 1.8 A resolution by using X-ray synchrotron data collected from a crystal flash-cooled with liquid nitrogen. The crystallographic agreement factors R and R(free) are, respectively, 18.3% and 24.0%. The asymmetric unit of the crystal contains a whole molecule that shows accurate 222-point group symmetry. The crystallized enzyme is a homotetramer of subunits with 484 residues, some 26 residues shorter than predicted from the DNA sequence. Mass spectrometry analysis confirmed the absence of 26 N-terminal residues, possibly removed by a periplasmic transport system. The core structure of the CatF subunit was closely related to seven other catalases with root-mean-square deviations (RMSDs) of 368 core Calpha atoms of 0.99-1.30 A. The heme component of CatF is heme b in the same orientation that is found in Escherichia coli hydroperoxidase II, an orientation that is flipped 180 degrees with respect the orientation of the heme in bovine liver catalase. NADPH is not found in the structure of CatF because key residues required for nucleotide binding are missing; 2129 water molecules were refined into the model. Water occupancy in the main or perpendicular channel of CatF varied among the four subunits from two to five in the region between the heme and the conserved Asp150. A comparison of the water occupancy in this region with the same region in other catalases reveals significant differences among the catalases.

Binding Sites↗
PubMed2004

Monofunctional catalase P of Paracoccidioides brasiliensis: identification, characterization, molecular cloning and expression analysis.

Within the context of studies on genes from Paracoccidioides brasiliensis (Pb) potentially associated with fungus-host interaction, we isolated a 61 kDa protein, pI 6.2, that was reactive with sera of patients with paracoccidioidomycosis. This protein was identified as a peroxisomal catalase. A complete cDNA encoding this catalase was isolated from a Pb cDNA library and was designated PbcatP. The cDNA contained a 1509 bp ORF containing 502 amino acids, whose molecular mass was 57 kDa, with a pI of 6.5. The translated protein PbCATP revealed canonical motifs of monofunctional typical small subunit catalases and the peroxisome-PTS-1-targeting signal. The deduced and the native PbCATP demonstrated amino acid sequence homology to known monofunctional catalases and was most closely related to catalases from other fungi. The protein and mRNA were diminished in the mycelial saprobic phase compared to the yeast phase of infection. Protein synthesis and mRNA levels increased during the transition from mycelium to yeast. In addition, the catalase protein was induced when cells were exposed to hydrogen peroxide. The identification and characterization of the PbCATP and cloning and characterization of the cDNA are essential steps for investigating the role of catalase as a defence of P. brasiliensis against oxygen-dependent killing mechanisms. These results suggest that this protein exerts an influence in the virulence of P. brasiliensis.

Amino Acid Sequence↗
PubMed1993

Evidence that catalase is a major pathway of ethanol oxidation in vivo: dose-response studies in deer mice using methanol as a selective substrate.

Recently, it was demonstrated that 4-methylpyrazole was not only an inhibitor of alcohol dehydrogenase but also caused competitive inhibition of fatty acyl-CoA synthetase, the enzyme which activates fatty acids (B. U. Bradford, D. T. Forman, and R. G. Thurman, 1993, Mol. Pharmacol. 43, 115-119). Rates of catalase-dependent alcohol metabolism were decreased in alcohol dehydrogenase-negative (ADH-) deer mice because the H2O2 supply for catalase via peroxisomal fatty acid oxidation was inhibited due to substrate limitation. In light of these findings it became necessary to reevaluate the role of catalase and alcohol dehydrogenase in alcohol metabolism. In this study, methanol, a selective substrate for catalase in rodents, was compared with ethanol. Rates of ethanol and methanol metabolism were studied in vivo at blood alcohol levels ranging from 50 to 500 mg/dl. In the ADH- deer mouse, rates of methanol and ethanol metabolism increased when alcohol was elevated from 0 to 100 mg/dl and were maximal at values around 6-8 mmol/kg/h (half-maximal rates were observed at blood alcohol levels around 50 mg/dl). In the ADH+ deer mouse, rates of ethanol metabolism increased to values around 9 mmol/kg/h at 100 mg/dl and remained constant at blood levels up to 500 mg/dl. In contrast, rates of methanol metabolism increased to values of only 5 mmol/kg/h at levels of 100 mg/dl (the half-maximal rate was about 2.5 mmol/kg/h at 50 mg/dl) followed by a steady increase to 9 mmol/kg/h as the blood level was increased from 100 to 500 mg/dl (the half-maximal rate for this second component was around 6 mmol/kg/h at 300 mg/dl). Rates of methanol uptake were 50 +/- 4 nmol/min/mg protein in 10,000g pellets from ADH- deer mouse livers; however, methanol was not metabolized by isolated microsomes. The catalase inhibitor aminotriazole decreased ethanol and methanol metabolism 75% in ADH- deer mice. Further, olive oil, which is rich in oleate, increased methanol metabolism from 7 to 11.5 mmol/kg/h. This stimulation was blocked by fructose, which diminishes ATP and decreases H2O2 supply. In the ADH+ deer mouse, fructose (2 g/kg) stimulated ethanol metabolism as expected; however, inhibition of both ethanol and methanol metabolism was observed with higher doses of fructose (10 g/kg). Taken together, these data support the hypothesis that catalase is the predominant pathway for alcohol metabolism in the ADH- deer mouse. The contribution of catalase was about 50% in the ADH+ mutant at low doses of ethanol and approached 100% as the alcohol concentration was elevated.

Alcohol Dehydrogenase↗
PubMedDate not supplied

A new type of inherited catalase deficiencies: its characterization and comparison to the Japanese and Swiss type of acatalasemia.

Thirteen Hungarian families that exhibited inherited catalase deficiencies have been detected. Differences between the deficiencies reported from Hungary and the previously reported Swiss acatalasemia were characterized using biochemical analysis of the catalase proteins. Molecular biological methods were used to compare the previously reported types of catalase deficiencies in Japan and the Hungarian deficiencies. Three mutations (a GA insertion in exon 2, a G insertion in exon 2, and a T to G substitution in intron 7) are responsible for decreased catalase activity in 7 of the 13 Hungarian kindreds; the other 6 families have not yet been characterized. These are not the mutations observed in Japan. Changes in lipid and carbohydrate metabolism and the high incidence (12.7%) of diabetes mellitus in the Hungarian kindreds suggest that individuals with inherited catalase deficiency are at risk of atherosclerosis and diabetes mellitus. The Hungarian subjects were detected during screening of a large population for catalase activity; no overt disease state was associated with the deficiencies. We hypothesize that the increased risk of disease may be due to prolonged exposure to elevated levels of blood hydrogen peroxide due to the lack of normal removal of hydrogen peroxide by blood catalase.

Acatalasia↗
PubMed1995

Activation of DNA synthesis and expression of the JE gene by catalase in mouse osteoblastic cells: possible involvement of hydrogen peroxide in negative growth regulation.

The addition of catalase isolated from bovine liver to the culture medium of quiescent mouse osteoblastic MC3T3-E1 cells decreased intracellular oxidized state, determined using fluorescent dye and laser-scanning confocal microscopy. The decrease in intracellular oxidized state evoked by catalase seemed to be involved in the arrest of growth, since catalase increased the incorporation of [3H]thymidine in these quiescent cells. On gel filtration of the catalase preparation, catalase activity and the stimulation of DNA synthesis coincided. Of the early response genes, JE, which is induced by competence factors, was induced by catalase in this cell line, whereas c-fos, c-jun, and KC mRNA levels were not affected. Catalase isolated from fungi and glutathione peroxidase+glutathione added to the culture medium also increased the steady-state level of JE mRNA. These results indicate that cells in the quiescent state produce hydrogen peroxide endogenously and that hydrogen peroxide acts as one of the mediators inhibiting DNA synthesis as well as the expression of JE, a growth factor-inducible gene.

3T3 Cells↗
PubMed2000

Identification of epitopes for cross-reaction, auto-reaction and autoantibodies to catalase.

We identified in bovine and rat catalase two epitopes that were responsible for a cross-reaction between the two species using cross-reactive antibodies raised in rabbits by immunization with their respective catalases. The epitopes were(444)TFYLK(448)and(458)LCENIAGHLK(467)in bovine catalase and(445)TFYTK(449)and(459)LCENIANHLK(468)in rat catalase. The two epitopes in rats were also identified as epitopes for auto-reactive antibodies that were raised in rats by immunization with bovine catalase and were reactive with a homologous rat catalase. Furthermore, one of the rat epitopes,(459)LCENIANHLK(468), was identified as the epitope for autoantibodies which were inducible by intensive immunization in rats with the homologous rat catalase. A possible implication of the epitopes in certain human diseases is discussed.

Amino Acid Sequence↗
PubMed1999

Structure of catalase-A from Saccharomyces cerevisiae.

The structure of the peroxisomal catalase A from the budding yeast Saccharomyces cerevisiae, with 515 residues per subunit, has been determined and refined to 2.4 A resolution. The crystallographic agreement factors R and Rfree are 15.4% and 19.8%, respectively. A tetramer with accurate 222-molecular symmetry is located in the asymmetric unit of the crystal. The conformation of the central core of catalase A, about 300 residues, remains similar to the structure of catalases from distantly related organisms. In contrast, catalase A lacks a carboxy-terminal domain equivalent to that found in catalase from Penicillium vitalae, the only other fungal catalase structure available. Structural peculiarities related with the heme and NADP(H) binding pockets can be correlated with biochemical characteristics of the catalase A enzyme. The network of molecular cavities and channels, filled with solvent molecules, supports the existence of one major substrate entry and at least two possible alternative pathways to the heme active site. The structure of the variant protein Val111Ala, also determined by X-ray crystallography at 2.8 A resolution, shows a few, well-localized, differences with respect to the wild-type enzyme. These differences, that include the widening of the entry channel in its narrowest point, provide an explanation for both the increased peroxidatic activity and the reduced catalatic activity of this mutant.

Alanine↗
PubMed2000

Active and inhibited human catalase structures: ligand and NADPH binding and catalytic mechanism.

Human catalase is an heme-containing peroxisomal enzyme that breaks down hydrogen peroxide to water and oxygen; it is implicated in ethanol metabolism, inflammation, apoptosis, aging and cancer. The 1. 5 A resolution human enzyme structure, both with and without bound NADPH, establishes the conserved features of mammalian catalase fold and assembly, implicates Tyr370 as the tyrosine radical, suggests the structural basis for redox-sensitive binding of cognate mRNA via the catalase NADPH binding site, and identifies an unexpectedly substantial number of water-mediated domain contacts. A molecular ruler mechanism based on observed water positions in the 25 A-long channel resolves problems for selecting hydrogen peroxide. Control of water-mediated hydrogen bonds by this ruler selects for the longer hydrogen peroxide and explains the paradoxical effects of mutations that increase active site access but lower catalytic rate. The heme active site is tuned without compromising peroxide binding through a Tyr-Arg-His-Asp charge relay, arginine residue to heme carboxylate group hydrogen bonding, and aromatic stacking. Structures of the non-specific cyanide and specific 3-amino-1,2, 4-triazole inhibitor complexes of human catalase identify their modes of inhibition and help reveal the catalytic mechanism of catalase. Taken together, these resting state and inhibited human catalase structures support specific, structure-based mechanisms for the catalase substrate recognition, reaction and inhibition and provide a molecular basis for understanding ethanol intoxication and the likely effects of human polymorphisms.

Amino Acid Sequence↗
PubMed1999

Peroxide-inducible catalase in Aeromonas salmonicida subsp. salmonicida protects against exogenous hydrogen peroxide and killing by activated rainbow trout, Oncorhynchus mykiss L., macrophages.

Aeromonas salmonicida subsp. salmonicida expresses a single cytoplasmically located catalase which was found to be inducible by exposure to 20 microM hydrogen peroxide in mid-exponential phase resulting in a 4 fold increase in activity. Subsequent exposure to 2 mM peroxide in late-exponential/early-stationary phase resulted in further induction of catalase activity which increased to 20 fold higher levels than those found in uninduced cultures. Exponentially induced cultures were protected against subsequent exposure to 10 mM peroxide which was lethal to non-induced cultures. Bacteria subjected to induction in mid-exponential and early-stationary phase were resistant to 100 mM peroxide, although viability was greatly reduced. Growth of the bacterium under iron-restricted conditions had no effect on the peroxide induction of catalase. As current evidence indicates, the latter is an iron-co-factored heme catalase, this result suggests that catalase induction has a high priority in the metabolism of iron. Furthermore, exposure to peroxide also induces expression of periplasmic MnSOD. A. salmonicida MT423 was resistant to normal rainbow trout macrophages, but was susceptible to killing by activated macrophages. However, if catalase was induced by prior exposure to 20 microM peroxide during mid-exponential phase, A. salmonicida was resistant to killing by activated macrophages. The ability of A. salmonicida to upregulate periplasmic MnSOD and cytoplasmic catalase production under iron restricted conditions and low level peroxide (conditions expected to exist during the early stages of an infection) may be vital for its ability to withstand attack by phagocytic cells in vivo.

Aeromonas↗