Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CATALASE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,279 records · Page 71Linked to original sources
PubMed1989

Endotoxin pretreatment increases endogenous myocardial catalase activity and decreases ischemia-reperfusion injury of isolated rat hearts.

Hearts isolated from rats pretreated 24 hr before with endotoxin had increased myocardial catalase activity, but the same superoxide dismutase, glutathione peroxidase, glutathione reductase, and glucose-6-phosphate dehydrogenase activities, as hearts from untreated rats. Hearts isolated from rats pretreated with endotoxin 24 hr before also had increased myocardial function (decreased injury) after ischemia and reperfusion (Langendorff apparatus, 37 degrees C), as assessed by measurement of ventricular developed pressure, contractility (+dP/dt), and relaxation rate (-dP/dt), compared to control hearts. In contrast, hearts isolated from rats pretreated with endotoxin 1 hr before isolation or hearts perfused with endotoxin did not have increased catalase activity or decreased injury following ischemia and reperfusion. Aminotriazole pretreatment prevented increases in myocardial catalase activity and myocardial function after ischemia-reperfusion in hearts from endotoxin-pretreated rats. The results suggest that endotoxin pretreatment decreases cardiac ischemia-reperfusion injury and that increases in endogenous myocardial catalase activity contribute to protection.

Amitrole↗
PubMed1995

Simultaneous overexpression of copper- and zinc-containing superoxide dismutase and catalase retards age-related oxidative damage and increases metabolic potential in Drosophila melanogaster.

The objective of this study was to elucidate the nature of the mechanisms by which overexpression of copper- and zinc-containing superoxide dismutase (Cu,Zn-SOD) and catalase extends life span of Drosophila melanogaster. Experimental flies containing single extra doses of Drosophila Cu,Zn-SOD and catalase genes were compared with appropriate controls at different ages. Overexpression of Cu,Zn-SOD and catalase caused a retardation in the accumulation of 8-hydroxydeoxyguanosine during aging and in response to the exposure of live flies to x-rays. The age-related loss of glucose-6-phosphate dehydrogenase activity (Glu-6-P dehydrogenase) and the increase in the rate of mitochondrial H2O2 generation were less steep in the experimental than control flies. The rate of in vivo oxygen consumption in the latter two-thirds of life span was higher in the experimental than in the control flies. Furthermore, the metabolic potential, or the total amount of oxygen consumed during an average life span, was about 30% greater in the experimental than the control flies. Altogether, results of this study indicate that overexpression of Cu,Zn-SOD and catalase ameliorates the age-related accumulation of molecular oxidative damage and susceptibility to such damage in response to acute oxidative stress while prolonging the metabolic life of flies. The concept that oxidative stress is a causal factor in the aging process is supported.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1996

Molecular cloning of manganese catalase from Lactobacillus plantarum.

A genomic clone encoding manganese-containing catalase has been isolated from lactic acid bacterium Lactobacillus plantarum, sequenced, and expressed in Escherichia coli cells with an inducible expression system. The primary structure of the enzyme deduced from the nucleotide sequence, that comprises 266 amino acid residues, showed no significant homology with that of any other proteins registered on the available data bases. No peptide motifs conserved among active sites of proteins including manganese-containing enzymes were found. The E. coli cells carrying an expression construct, in which the 5'-noncoding region of the manganese catalase gene was replaced with the lac promoter, highly induced a protein reacting with the antiserum to manganese catalase. The prediction of secondary structure from the deduced primary structure suggested that the L. plantarum manganese catalase, that is classified as a novel protein on the basis of its primary structure, has a main structural motif formed by four near parallel helices between which is the catalytic site manganese.

Amino Acid Sequence↗
PubMed2003

An electrical potential in the access channel of catalases enhances catalysis.

Substrate H2O2 must gain access to the deeply buried active site of catalases through channels of 30-50 A in length. The most prominent or main channel approaches the active site perpendicular to the plane of the heme and contains a number of residues that are conserved in all catalases. Changes in Val169, 8 A from the heme in catalase HPII from Escherichia coli, introducing smaller, larger or polar side chains reduces the catalase activity. Changes in Asp181, 12 A from the heme, reduces activity by up to 90% if the negatively charged side chain is removed when Ala, Gln, Ser, Asn, or Ile are the substituted residues. Only the D181E variant retains wild type activity. Determination of the crystal structures of the Glu181, Ala181, Ser181, and Gln181 variants of HPII reveals lower water occupancy in the main channel of the less active variants, particularly at the position forming the sixth ligand to the heme iron and in the hydrophobic, constricted region adjacent to Val169. It is proposed that an electrical potential exists between the negatively charged aspartate (or glutamate) side chain at position 181 and the positively charged heme iron 12 A distant. The potential field acts upon the electrical dipoles of water generating a common orientation that favors hydrogen bond formation and promotes interaction with the heme iron. Substrate hydrogen peroxide would be affected similarly and would enter the active site oriented optimally for interaction with active site residues.

Arginine↗
PubMed2005

Catalase plays a critical role in the CSF-independent survival of human macrophages via regulation of the expression of BCL-2 family.

M-colony-stimulating factor (M-CSF)-induced monocyte-derived macrophages (M-Mphi) required continuous presence of M-CSF for their survival, and depletion of M-CSF from the culture induced apoptosis, whereas human alveolar macrophages (A-Mphi) and granulocyte-macrophage (GM)-CSF-induced monocyte-derived macrophages (GM-Mphi) survived even in the absence of CSF. The expression of BCL-2 was higher in M-Mphi, and M-CSF withdrawal down-regulated the expression. The expression of BCL-X(L) was higher in A-Mphi and GM-Mphi, and the expression was CSF-independent. The expression of MCL-1 and BAX were not different between M-Mphi and GM-Mphi and were CSF-independent. Down-regulation of the expression of BCL-2 and BCL-X(L) by RNA interference showed the important role of BCL-2 and BCL-X(L) in the survival of M-Mphi and GM-Mphi, respectively. Human erythrocyte catalase (HEC) and conditioned medium obtained from GM-Mphi or A-Mphi cultured in the absence of GM-CSF prevented the M-Mphi from apoptosis and restored the expression of BCL-2. The activity of the conditioned medium was abrogated by pretreatment with anti-HEC antibody. Anti-HEC antibody also induced the apoptosis of M-Mphi cultured in the presence of M-CSF and GM-Mphi and A-Mphi cultured in the presence or absence of GM-CSF and down-regulated the expression of BCL-2 and BCL-X(L) in these Mphis. GM-Mphi and A-Mphi, but not M-Mphi, can produce both extracellular catalase and cell-associated catalase in a CSF-independent manner. Intracellular glutathione levels were kept equivalent in these Mphis, both in the presence or absence of CSF. These results indicate a critical role of extracellular catalase in the survival of human macrophages via regulation of the expression of BCL-2 family genes.

Apoptosis↗
PubMed1996

Exogenous catalase may potentiate oxidant-mediated lung injury in the female Sprague-Dawley rat.

Enhancement of lung antioxidant capacity has been proposed in the therapy of acute lung injuries involving local accumulation of reactive oxygen species (ROS). We have studied in the female Sprague-Dawley rat the effect of intratracheal administration of catalase (CAT) on the acute lung response induced by different ROS generating systems. The lung response was assessed at several time intervals (60-360 min) by monitoring in bronchoalveolar fluid (BALF) the activity of lactate dehydrogenase and the levels of total protein, albumin, and glucose. While CAT (50,000 IU/rat) significantly reduced the biochemical changes induced by hydrogen peroxide produced by a glucose/glucose oxidase system, it markedly exacerbated the lesions induced by phorbol myristate acetate (PMA). Several observations indicate that a particular chemical species formed during the catalase inactivation process is responsible for this effect. Parallel to the development of the lung damage, we noted a rapid reduction of CAT activity (80%) in the BALF of animals treated with PMA and CAT. In vitro an inhibition of CAT activity was observed in the presence of a superoxide anion generating system, and this inhibition was prevented by superoxide dismutase (SOD). A dose of 10,000 IU superoxide dismutase did not prevent the development of the lung lesions induced by PMA plus CAT. Administered alone or in association with PMA, CAT inactivated by heat or 3-aminotriazole also caused severe lung damage. In conclusion, the present study indicates that exogenous catalase may not always protect against the inflammatory reaction resulting from an oxidative stress. In the presence of superoxide anions, catalase may aggravate the lesions, and this possibility should be kept in mind when considering an antioxidant therapy.

Albumins↗
PubMed1987

Effects of peroxide and catalase on near ultraviolet radiation sensitivity in Escherichia coli strains.

The role of peroxide and catalase on NUV radiation sensitivity was examined in two repair competent E. coli strains, AB1157 and B/r. Exponential phase B/r is considerably more sensitive to NUV radiation than exponential phase AB1157. However, resistance to 5 mmol dm-3 H2O2 was induced in both AB1157 and B/r by pretreating growing cells with 30 mumol dm-3 H2O2. Pretreatment also induced resistance to broad-band NUV radiation in these strains. The addition of catalase to the post-irradiation plating medium increased survival to the same extent as that provided by pretreatment with 30 mumol dm-3 H2O2, in both strains. The NUV radiation sensitivity seen in B/r does not appear to be due to a deficiency in enzymes that scavenge H2O2, as a catalase deficient mutant, E. coli UM1, is more resistant to NUV radiation than B/r. Also, assays for H2O2 scavenging ability show little difference between AB1157 and B/r in this respect. Two hypotheses are put forward to account for the sensitivity of exponential phase B/r. Whilst it is apparent that peroxides and catalase do have a role in NUV radiation damage, it is clear that other factors also influence survival under certain conditions.

Catalase↗
PubMed2003

Adenosine deaminase enzyme activity is increased and negatively correlates with catalase, superoxide dismutase and glutathione peroxidase in patients with Behçet's disease: original contributions/clinical and laboratory investigations.

AIM: Behçet's disease (BD) is an inflammatory vasculitis with immunologic, endothelial and neutrophil alterations. Adenosine deaminase (AD) is a marker of T-cell activation and is related to the production of reactive oxygen species by neutrophils with the production of NO(*), O(2)(*-), H(2)O(2) and OH(*). We reported increased tumour necrosis factor-alpha, soluble interleukin-2 receptor, interleukin-6, interleukin-8 and NO(*) in active BD. As there is a relation between cytokines, T cells and oxidative stress in inflammatory diseases, this study further evaluated: (1) plasma AD activity and its correlation with acute phase reactants; (2) thiobarbituric acid-reactive substances (TBARS) as an indicator for lipid peroxidation; and (3) antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GSHPx) and catalase in patients with BD. The effect of disease activity and correlations between the measured parameters were explored. METHODS: A total of 35 active (n=17) or inactive (n=18) patients with BD (16 men, 19 women) satisfying International Study Group criteria, and 20 age-matched and sex-matched controls (nine men, 11 women) were included in this cross-sectional case-control study. AD and TBARS were measured in plasma, catalase in red blood cells (RBC), and SOD and GSHPx in both plasma and RBC in both groups. Acute phase reactants (alpha(1)-antitrypsin, alpha(2)-macroglobulin, neutrophils, erythrocyte sedimentation rate) were used to classify patients as active or inactive. RESULTS: Plasma AD (mean+/-standard error of the mean, 36.1+/-0.7 U/l) and TBARS (4.2+/-0.1 nmol/ml) levels were significantly (for each, p<0.001) higher in BD than in controls (24.1+/-0.8 U/l and 1.6+/-0.1 nmol/ml, respectively). RBC catalase activity was significantly (p<0.001) lower in BD than in controls (120.9+/-3.8 versus 160.3+/-4.1 k/g haemoglobin). SOD and GSHPx activities were significantly lower in both plasma and erythrocytes of patients with BD than in controls (plasma SOD, 442.4+/-8.6 versus 636.4+/-9.2 U/ml, p<0.001; RBC SOD, 3719.2+/-66.0 versus 4849.7+/-49.0 U/g haemoglobin, p<0.001; plasma GSHPx, 73.1+/-1.5 versus 90.6+/-2.9 U/ml, p<0.001; RBC GSHPx, 600.7+/-8.0 versus 670.6+/-10.1 U/g haemoglobin, p<0.001). Active BD patients had significantly lower antioxidant enzymes (except RBC catalase) and higher AD and TBARS levels than inactive subjects (for each, p<0.01). When considering all BD patients, a significant positive correlation was present between AD and TBARS (p<0.001) whereas both AD and TBARS were negatively correlated with antioxidant enzymes (for each, p<0.05). CONCLUSIONS: AD and lipid peroxidation are increased and associated with defective antioxidants in BD, suggesting interactions between activated T cells and neutrophil hyperfunction. Measures of pro-oxidative stress and antioxidative defence with AD activity as an indicator of T-cell activation can be considered as significant supportive diagnostic indicators, especially in active disease. In addition, strengthening the antioxidant defence may contribute to treatment modalities.

Acute-Phase Proteins↗
PubMed2003

Oxidative damage to catalase induced by peroxyl radicals: functional protection by melatonin and other antioxidants.

Thermal decomposition by the azo initiator 2,2' azobis(2-amidinopropane) dihydrochloride (AAPH) has been widely used as a water-soluble source of free radical initiators capable of inducing lipid peroxidation and protein damage. Here, in a lipid-free system, AAPH alone (40 mM) rapidly induced protein modification and inactivation of the enzyme catalase (EC 1.11.1.6). Using SDS-PAGE, it was shown that protein band intensity is dramatically reduced after 4 h of incubation with AAPH, leading to protein aggregation. Several antioxidants including melatonin, glutathione (GSH) and trolox prevented catalase modification when used at a 250 microM concentration whereas ascorbate was only effective at 1 mM concentration. All the antioxidants tested reduced carbonyl formation although melatonin was the most effective in this regard. Enzyme inactivation caused by AAPH was also significantly reduced by the antioxidants and again melatonin was more efficient than the other antioxidants used in this study. Results shown here demonstrate that alkyl peroxyl radicals inactivate catalase and reduce the effectiveness of cells to defend against free radical damage; the damage to catalase can be prevented by antioxidants, especially melatonin.

Amidines↗
PubMed2006

Non-oxygen-forming pathways of hydrogen peroxide degradation by bovine liver catalase at low hydrogen peroxide fluxes.

Heme catalases are considered to degrade two molecules of H(2)O(2) to two molecules of H(2)O and one molecule of O(2) employing the catalatic cycle. We here studied the catalytic behaviour of bovine liver catalase at low fluxes of H(2)O(2) (relative to catalase concentration), adjusted by H(2)O(2)-generating systems. At a ratio of a H(2)O(2) flux (given in microM/min(- 1)) to catalase concentration (given in microM) of 10 min(- 1) and above, H(2)O(2) degradation occurred via the catalatic cycle. At lower ratios, however, H(2)O(2) degradation proceeded with increasingly diminished production of O(2). At a ratio of 1 min(- 1), O(2) formation could no longer be observed, although the enzyme still degraded H(2)O(2). These results strongly suggest that at low physiological H(2)O(2) fluxes H(2)O(2) is preferentially metabolised reductively to H(2)O, without release of O(2). The pathways involved in the reductive metabolism of H(2)O(2) are presumably those previously reported as inactivation and reactivation pathways. They start from compound I and are operative at low and high H(2)O(2) fluxes but kinetically outcompete the reaction of compound I with H(2)O(2) at low H(2)O(2) production rates. In the absence of NADPH, the reducing equivalents for the reductive metabolism of H(2)O(2) are most likely provided by the protein moiety of the enzyme. In the presence of NADPH, they are at least in part provided by the coenzyme.

Animals↗
PubMed1997

Influence of Mycobacterium tuberculosis catalase gene (KatG) expression on nitric oxide production and the intracellular growth of transfected Mycobacterium smegmatis strains within murine macrophages.

Expression or possession of catalase gene may interfere with the iNOS/NO pathway in mycobacteria, hence altering their capacity to survive within macrophages. Therefore, strains of M. smegmatis with an inactive catalase-peroxidase gene (KatG), or into which the KatG gene of Mycobacterium tuberculosis had been transfected, were used to study the influence of catalase on nitric oxide (NO) production and mycobacterial survival within infected murine 1774 macrophages. High levels of nitrite (40-70 nM) were detected in IFN-gamma and LPS activated, infected murine cell culture supernatants, however, NO2- titres produced by infected murine cells did not differ between various catalase phenotype strains. Similarly, no significant difference in mycobacterial killing was also observed among the five strains of M. smegmatis tested over a 3 day infection period.

Animals↗
PubMed1969

Cytochemical localization of peroxidatic activity of catalase in rat hepatic microbodies (peroxisomes).

Prominent staining of rat hepatic microbodies was obtained by incubating sections of aldehyde-fixed rat liver in a modified Graham and Karnovsky's medium for ultrastructural demonstration of peroxidase activity. The electron-opaque reaction product was deposited uniformly over the matrix of the microbodies. The microbodies were identified by their size, shape, presence of tubular nucleoids, and other morphologic characteristics, and by their relative numerical counts. The staining reaction was inhibited by the catalase inhibitor, aminotriazole, and by KCN, azide, high concentrations of H(2)O(2), and by boiling of sections. These inhibition studies suggest that the peroxidatic activity of microbody catalase is responsible for the staining reaction. In the absence of exogenous H(2)O(2) appreciable staining of microbodies was noted only after prolonged incubation. Addition of sodium pyruvate, which inhibits endogenous generation of H(2)O(2) by tissue oxidases, or of crystalline catalase, which decomposes such tissue-generated H(2)O(2), completely abolished microbody staining in the absence of H(2)O(2). Neither diaminobenzidine nor the product of its oxidation had any affinity to bind nonenzymatically to microbody catalase and thus stain these organelles. The staining of microbodies was optimal at alkaline pH of 8.5. The biological significance of this alkaline pH in relation to the similar pH optima of several microbody oxidases is discussed. In addition to staining of microbodies, a heat-resistant peroxidase activity is seen in some of the peribiliary dense bodies. The relation of this reaction to the peroxidase activity of lipofuscin pigment granules is discussed.

Animals↗
PubMed1973

The synthesis and turnover of rat liver peroxisomes. V. Intracellular pathway of catalase synthesis.

The subcellular distribution of the biosynthetic intermediates of catalase was studied in the livers of rats receiving a mixture of [(3)H]leucine and [(14)C]delta-aminolevulinic acid by intraportal injection. Postnuclear supernates were fractionated by a one-step gradient centrifugation technique that separates the main subcellular organelles, partly on the basis of size, and partly on the basis of density. Labeled catalase and its biosynthetic intermediates were separated from the gradient fractions by immunoprecipitation, and the distributions of radioactivity were compared with those of marker enzymes. The results show that catalase protein is synthesized outside the peroxisomes, but rapidly appears in these particles, mostly still in the form of the first hemeless biosynthetic intermediate. Addition of heme and completion of the catalase molecule take place within the peroxisomes. During the first 15 min after [(3)H]leucine administration, more than half of the newly formed first intermediate was recovered in the supernatant fraction, where it was found to exist as an aposubunit of about 60,000 molecular weight.

Aminolevulinic Acid↗
PubMed1970

An ultrastructural study of glomerular permeability in aminonucleoside nephrosis using catalase as a tracer protein.

Beef liver catalase (mol wt 240,000) was injected intravenously into normal rats and rats made nephrotic with aminonucleoside of puromycin. The localization of the tracer in the kidneys was then studied by ultrastructural cytochemistry, 3 min-12 hr after injection. Passage of catalase into the urinary space in normal rats was restricted by the basement membrane and by the epithelial slit pore. Nephrotic glomeruli showed extensive fusion of foot processes and formation of pockets and vacuoles in the fused epithelium; within 3 min after injection, catalase appeared in basal pockets, epithelial vacuoles, and the urinary space. Residual slit pores and close junctions in fused epithelium were impermeable to catalase. These studies indicate that alteration of the epithelial cells and basement membrane is responsible for protein leakage in aminonucleoside nephrosis.

Animals↗
PubMed1991

Catalase-negative listeria monocytogenes causing meningitis in an adult. Clinical and laboratory features.

A 63-year-old previously healthy woman presented with acute meningitis. Cultures of the cerebrospinal fluid yielded a serotype 1/2a isolate of Listeria monocytogenes that was biochemically typical in all respects, other than the reproducible lack of catalase production. During therapy, the patient developed oculomotor dysfunction that was attributed to an abscess in the internal capsule. This case report documents the existence of catalase-negative L. monocytogenes indicating that catalase production should not be a strict criterion for identification of Listeria. Furthermore, this clinical experience extends in vitro and experimental animal studies indicating that catalase production is not a necessary virulence factor for invasion by Listeria.

Abscess↗
PubMed2003

Graft union formation in tomato plants: peroxidase and catalase involvement.

BACKGROUND AND AIMS: The use of grafted plants in vegetable crop production is now being expanded greatly. However, few data are available on the formation of graft unions in vegetables. In this work, the structural development of the graft union formation in tomato plants is studied, together with the possible relationship with activities of peroxidases and catalases. METHODS: Tomato (Lycopersicon esculentum Mill.) seedlings of cultivar Fanny were grafted on the rootstock of cultivar AR-9704 using the 'tongue approach grafting' method, and were grown in a crop chamber. A study of the structural development of the graft union and the involvement of peroxidases and catalases in the process of graft formation was carried out during the first stages of the graft union (4, 8 and 15 d after grafting). KEY RESULTS: Observation of the structure of the graft union showed formation of xylem and phloem vessels through the graft union 8 d after grafting. In addition, root hydraulic conductance, L0, indicate that the graft union is fully functional 8 d after grafting, which coincided with an increase of peroxidase and catalase activities. CONCLUSIONS: These results suggest that increased peroxidase and catalase activities might be implicated in graft development in tomato plants.

Biomechanical Phenomena↗
PubMed1993

Mutagenesis in Escherichia coli K-12 mutants defective in superoxide dismutase or catalase.

Escherichia coli K-12 strains with diminished levels of superoxide dismutase (SOD) due to inactivation of the sodA, sodB or sodA sodB genes were constructed in order to quantify the role of O2. in mutagenesis. Mutagenesis was monitored by selecting forward mutations to L-arabinose resistance (AraR). No sodA sodB mutant inability to grow in aerobic minimal medium was found, in contrast to that previously reported for a different E. coli wild-type genetic background. The role of SOD for coping with the damaging effects of superoxide became evident after the increase in intracellular O2-. flux by growing cells under hyperoxygenation, but particularly by using redox cycling compounds such as plumbagin, paraquat and menadione. Bacteria completely devoid of SOD activity showed very high levels of AraR-induced mutants at doses that were non-mutagenic for the SOD-proficient parental or the sodA or sodB single mutants. The mutagenicity of nifurtimox and quercetin were studied to further compare the responses of the SOD-deficient bacteria to those of their SOD-proficient counterparts. The relative importance of SOD and catalase for coping with the damaging effects of O2-. and H2O2 was quantified by comparing SOD-deficient bacteria with isogenic catalase-deficient cells (a katG katE double mutant). The mutagenicities of plumbagin and menadione were much higher in SOD-deficient than in catalase-deficient bacteria, in agreement with the role of the O2-. radical in the so-called metal-catalyzed Haber-Weiss reaction. The relevance of catalase in protecting against the damaging effects of H2O2 was evident from the hypersensitivity of the katG katE double mutant to the mutagenic and lethal effects of this oxidizing agent. It is concluded that the Ara mutagenicity assay combined with depletion in specific antioxidative enzymes could be a tool in establishing the extent to which DNA damage by oxygen radicals is relevant to mutagenesis.

Bacterial Proteins↗
PubMed1993

Increased formation of 8-hydroxydeoxyguanosine, an oxidative DNA damage, in lymphoblasts from Fanconi's anemia patients due to possible catalase deficiency.

Fanconi's anemia (FA) cells are highly susceptible to both reactive oxygen species and mitomycin C (MMC), a DNA cross-linking agent. In this study we have determined the amounts of 8-hydroxydeoxyguanosine (8OHdG), typical of oxidative DNA damage, in Epstein-Barr virus transformed lymphoblasts from FA patients and normal controls by the use of HPLC combined with electrochemical detection. FA cells (HSC72 and 99 cells being assigned to FA complementation group A) formed 2-3 times more 8OHdG than control cells after incubation with 20 mM H2O2 at 37 degrees C for 30 min. FA cells also formed more 8-hydroxyguanosine, typical of oxidative RNA damage, than control cells. FA cells showed decreased activity to decompose H2O2. Although the activity in FA cells was only 20-30% less than control cells, the remaining, undecomposed H2O2 concentration was almost twice as much in FA cells as in control cells, and the remaining H2O2 concentration correlated well with the amounts of 8OHdG formation. The H2O2 decomposing activity was almost completely inhibited by sodium azide (NaN3) or aminotriazole, both catalase inhibitors. With these inhibitors the amounts of 8OHdG formation were much higher than in those cells without inhibitors, and were almost the same in control cells as in FA cells. Catalase activity in FA cell lysates was 70-80% of controls. MMC also increased 8OHdG formation in FA cells only at ED100 but not at ED50. These results indicate that FA cells, at least FA complementation group A cells, have increased susceptibility to oxidative DNA damage, and that this increased susceptibility is possibly due to decreased catalase activity. These results also suggest that catalase plays an important role in protecting DNA from oxidative damage. However, this increased susceptibility to oxidative DNA damage is considered not to be the major cause of the increased susceptibility to MMC.

8-Hydroxy-2'-Deoxyguanosine↗