Production of Catalases by Aspergillus niger Isolates as a Response to Pollutant Stress by Heavy Metals

Isolates of Aspergillus niger, selected from the coal dust of a mine containing arsenic (As; 400 mg/kg) and from the river sediment of mine surroundings (As, 1651 mg/kg, Sb, 362 mg/kg), growing in minimal nitrate medium in the phase of hyphal development and spore formation, exhibited much higher levels of total catalase activity than the same species from the culture collection or a culture adapted to soil contaminated with As (5 mg/L). Electrophoretic resolution of catalases in cell-free extracts revealed three isozymes of catalases and production of individual isozymes was not significantly affected by stress environments. Exogenously added stressors (As⁵⁺, Cd²⁺, Cu²⁺) at final concentrations of 25 and 50 mg/L and H₂O₂ (20 or 40 mM) mostly stimulated production of catalases only in isolates from mines surroundings, and H₂O₂ and Hg²⁺ caused the disappearance of the smallest catalase I. Isolates exhibited a higher tolerance of the toxic effects of heavy metals and H₂O₂, as monitored by growth, than did the strain from the culture collection.     

Salicylic acid and H2O2 function by independent pathways in the induction of freezing tolerance in potato

The effects of salicylic acid (SA) and hydrogen peroxide (H₂O₂) on freezing tolerance were studied in two potato (Solanum tuberosum) cultivars (Alpha and Atlantic) that differ in cold sensitivity, Alpha being more tolerant to freezing than Atlantic. Lowest freezing survival rates were observed in 4-week-old plants. Freezing treatments consisting of exposure to 6° C for 4 h in the dark were applied 24 h after plants had been transferred from in vitro culture to soil. Catalase activity and H₂O₂ were estimated at the following harvest points: stage (a) 4-week-old in vitro plants treated with either 0.1 mM SA or 5 mM H₂O₂; stage (b) as in (a) but 24 h following transfer to soil prior to freezing treatment; stage (c) as in (b) but measured 15 days after a 4-h freezing treatment. The results show that (1) SA induced freezing tolerance in both cultivars; (2) SA inhibited ascorbate peroxidase activities in both cultivars at all harvest points but inhibited catalase activities in only at stage (a); (3) SA induced H₂O₂ accumulation only in Atlantic at stage (a); (4) H₂O₂ enhanced shoot catalase activities in Atlantic at stages (a) and (b) whereas this treatment had no effect on shoot catalase activities in Alpha; (5) H₂O₂ treatment induced freezing tolerance in Atlantic, even though shoot catalase activities were lower than those of the controls following exposure to freezing temperatures. We conclude that SA does not always lead to H₂O₂ accumulation even though catalase and ascorbate peroxidase activities are decreased as a result of the treatment. Moreover, H₂O₂ accumulation is not always associated with the induction of freezing tolerance, for example at stage (a) where SA-induced tolerance in Alpha was not accompanied by H₂O₂ accumulation. H₂O₂ was able to induce freezing tolerance only in Atlantic, even though H₂O₂ accumulated in both cultivars following this treatment.     

Kinetic Characterization of Extracellular Catalases fromPenicillium piceum F-648 and Its Hydrogen Peroxide-Adapted Variants

A comparative kinetic study of extracellular catalases produced by Penicillium piceum F-648 and their variants adapted to H₂O₂ was performed in culture liquid filtrates. The specific activity of catalase, the maximum rate of catalase-induced H₂O₂ degradation (V _max), V _max/K _M ratio, and the catalase inactivation rate constant in the enzymatic reaction (k _in, s^–1) were estimated in phosphate buffer (pH 7.4) at 30°C. The effective constant representing the rate of catalase thermal inactivation (k _in ^*, s^–1) was determined at 45°C. In all samples, the specific activity and K _M for catalase were maximum at a protein concentration in culture liquid filtrates of (2.5–3.5) × 10^–4 mg/ml. The effective constants describing the rate of H₂O₂ degradation (k, s^–1) were similar to that observed in the initial culture. These values reflected a twofold decrease in catalase activity in culture liquid filtrates. We hypothesized that culture liquid filtrates contain two isoforms of extracellular catalase characterized by different activities and affinities for H₂O₂. Catalases from variants 5 and 3 with high and low affinities for H₂O₂, respectively, had a greater operational stability than the enzyme from the initial culture. The method of adaptive selection for H₂O₂ can be used to obtain fungal variants producing extracellular catalases with improved properties.     

Factors determining the degree of anaerobiosis of Bifidobacterium strains

Summary The degree of sensitivity of twelve Bifidobacterium (Lactobacillus bifidus) strains to O₂ was determined by measuring the size of the inhibition zones obtained when the bacteria were grown in deep agar cultures under air, and by measuring growth in aerated cultures. The size of the inhibition zones varied from 1 to 23 mm. Growth in aerated cultures differed markedly for the strains investigated. No strain grew on agar plates under aerobic conditions.The small inhibition zone of three Bifidobacterium strains might be explained by the presence of a weak catalase activity, which removes traces of H₂O₂ possibly formed. It is also possible that the NADH oxidase of these strains does not form H₂O₂ at all. Most probably, the lack of growth on an agar medium results from the fact that these strains only grow below a certain oxidation-reduction potential.One strain, which was rather insensitive to O₂, formed a small amount of H₂O₂ from NADH oxidation. The absence of H₂O₂ in aerated liquid cultures and cell suspensions of this strain, which lacked catalase and NAD peroxidase activity, must be explained by removal of the traces of H₂O₂ formed, by an unknown peroxidase system or by a chemical reaction with pyruvate formed during glucose fermentation.For two strains, which were moderately sensitive to O₂, accumulation of H₂O₂ seems to be the principal reason for anaerobiosis. H₂O₂ turned out to inactivate specifically fructose-6-phosphate phosphoketolase, a key enzyme of the fermentation pathway of bifidobacteria.In the culture medium of two strains, which were extremely sensitive to O₂, no H₂O₂ could be detected after aeration. During anaerobic growth of these strains, the oxidation-reduction potential of the culture decreased so much that neutral red was decolourized. Cell suspensions of these strains only fermented glucose when cysteine was added. It was concluded that these strains required a low oxidation-reduction potential for growth and fermentation.     

A hydrogen peroxide safety valve: The reversible phosphorylation of catalase from the freeze-tolerant North American wood frog,Rana sylvatica

BackgroundThe North American wood frog, Rana sylvatica, endures whole body freezing while wintering on land and has developed multiple biochemical adaptations to elude cell/tissue damage and optimize its freeze tolerance. Blood flow is halted in the frozen state, imparting both ischemic and oxidative stress on cells. A potential build-up of H₂O₂ may occur due to increased superoxide dismutase activity previously discovered. The effect of freezing on catalase (CAT), which catalyzes the breakdown of H₂O₂ into molecular oxygen and water, was investigated as a result.MethodsThe present study investigated the purification and kinetic profile of CAT in relation to the phosphorylation state of CAT from the skeletal muscle of control and frozen R. sylvatica.ResultsCatalase from skeletal muscle of frozen wood frogs showed a significantly higher V_max (1.48 fold) and significantly lower K_m for H₂O₂ (0.64 fold) in comparison to CAT from control frogs (5 °C acclimated). CAT from frozen frogs also showed higher overall phosphorylation (1.73 fold) and significantly higher levels of phosphoserine (1.60 fold) and phosphotyrosine (1.27 fold) compared to control animals. Phosphorylation via protein kinase A or the AMP-activated protein kinase significantly decreased the K_m for H₂O₂ of CAT, whereas protein phosphatase 2B or 2C action significantly increased the K_m.ConclusionThe physiological consequence of freeze-induced CAT phosphorylation appears to improve CAT function to alleviate H₂O₂ build-up in freezing frogs.General significanceAugmented CAT activity via reversible phosphorylation may increase the ability of R. sylvatica to overcome oxidative stress associated with ischemia.     

Resistance of Penicillium piceum F-648 to Hydrogen Peroxide under Short-Term and Prolonged Oxidative Stress

Resistance of Penicillium piceumF-648 to hydrogen peroxide under short-term and prolonged oxidative stress was studied. An increase in the activity of intracellular catalase in fungal cells after short-term exposure to hydrogen peroxide was shown. Activation of fungal cells induced by H₂O₂ depends on the H₂O₂ concentration, time of exposure, and growth phase of the fungus. Variants of P. piceum F-648 that produced two forms of extracellular catalase with different catalytic properties were obtained due to prolonged adaptation to H₂O₂. Catalase with low affinity for substrate was produced predominantly by the parent culture and variant 3; however, a high substrate affinity of catalase was observed in variant 5. Variant 5 of P. piceum F-648 displayed a high catalytic activity and operational stability of catalase in the presence of phosphate ions and a concentration of substrate less than 30 mM at pH more than 7.     

Hydrogen peroxide scavenging is not a virulence determinant in the pathogenesis of Haemophilus influenzae type b strain Eagan

Background  

A potentially lethal flux of hydrogen peroxide (H₂O₂) is continuously generated during aerobic metabolism. It follows that aerobic organisms have equipped themselves with specific H₂O₂ dismutases and H₂O₂ reductases, of which catalase and the alkyl hydroperoxide reductase (AhpR) are the best-studied prokaryotic members. The sequenced Haemophilus influenzae Rd genome reveals one catalase, designated HktE, and no AhpR. However, Haemophilus influenzae type b strain Eagan (Hib), a causative agent of bacterial sepsis and meningitis in young children, disrupted in its hktE gene is not attenuated in virulence, and retains the ability to rapidly scavenge H₂O₂. This redundancy in H₂O₂-scavenging is accounted for by peroxidatic activity which specifically uses glutathione as the reducing substrate.     

Efficiency of bovine liver catalase as a catalyst to cleave H2O2 added continually to buffer solutions

Empirical estimations of H₂O₂ concentration in a system containing bovine liver catalase and continually supplied with H₂O₂ were done to evaluate the efficiency of the enzyme to cleave H₂O₂. It was found that the continuous addition of H₂O₂ leads to the formation of steady-state concentrations of H₂O₂ in the medium. At a constant catalase concentration both the level and the duration of the steady state are dependent on the flow rate of H₂O₂. The increase of the catalase concentration in the medium does not change the steady-state level, it merely leads to the maintenance of the steady state for longer durations. At higher flow rates of H₂O₂, no steady state could be maintained, even when catalase was present in high excess. The incomplete cleavage of H₂O₂ by catalase under these conditions is due to the low affinity of catalase toward H₂O₂ (high K_m value, apparent K_m = 0.1M H₂O₂) and to the rapid inactivation of the enzyme during the continuous addition of H₂O₂.     

Catalase activity and hydrogen peroxide levels are inversely correlated in maize scutella during seed germination

Abstract

Temporal patterns of hydrogen peroxide (H₂O₂) levels and total catalase activity are presented for post-imbibition scutella from six maize inbred lines expressing variable catalase activity. In all lines examined, H₂O₂ levels were highest during the initial days post-imbibition (1–2 dpi) and decreased thereafter, while total catalase activity was lowest during early dpi (1–2 dpi) and reached maximal activity at 4–6 dpi. In three of the six lines tested, a simple inverse correlation between catalase activity and H₂O₂ level was significant by Spearman's rank (P <0.01). In addition to the generaldecline in H₂O₂level throughout the dpi period, a reproducible increase in H₂O₂ level was observed at 4–5 dpi in five of six lines examined. Mutant lines lacking CAT-3 activity demonstrated a temporal shift in the occurrence of this increase. The role of total catalase (and individual isozymes) in controlling H₂O₂ levels during germination and the role of H₂O₂ as a potential regulator of catalase expression during germination are discussed.     

Photosynthetic electron flow affects H2O2 signaling by inactivation of catalase in Chlamydomonas reinhardtii

A specific signaling role for H₂O₂ in Chlamydomonas reinhardtii was demonstrated by the definition of a promoter that specifically responded to this ROS. Expression of a nuclear-encoded reporter gene driven by this promoter was shown to depend not only on the level of exogenously added H₂O₂ but also on light. In the dark, the induction of the reporter gene by H₂O₂ was much lower than in the light. This lower induction was correlated with an accelerated disappearance of H₂O₂ from the culture medium in the dark. Due to a light-induced reduction in catalase activity, H₂O₂ levels in the light remained higher. Photosynthetic electron transport mediated the light-controlled down-regulation of the catalase activity since it was prevented by 3-(3′4′-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II. In the presence of light and DCMU, expression of the reporter gene was low while the addition of aminotriazole, a catalase inhibitor, led to a higher induction of the reporter gene by H₂O₂ in the dark. The role of photosynthetic electron transport and thioredoxin in this regulation was investigated by using mutants deficient in photosynthetic electron flow and by studying the correlation between NADP-malate dehydrogenase and catalase activities. It is proposed that, contrary to expectations, a controlled down-regulation of catalase activity occurs upon a shift of cells from dark to light. This down-regulation apparently is necessary to maintain a certain level of H₂O₂ required to activate H₂O₂-dependent signaling pathways.     

Overexpression of Peroxisomal Malate Dehydrogenase MDH3 Gene Enhances Cell Death on H 2O 2 Stress in the ald5 Mutant of Saccharomyces cerevisiae

Mitochondrial aldehyde dehydrogenase ALD5 of Saccharomyces cerevisiae is involved in the biosynthesis of mitochondrial electron transport chain, and the ald5 mutant is incompetent for respiration. With use of the mutant, we examined the detoxication of H₂O₂ generation by fatty acid -oxidation in peroxisome. The ald5 mutant (AKD321), as well as the 746 ⁰ mutant, was more resistant to H₂O₂ stress than the wild type. However, overexpression of the MDH3 gene that was involved in the reoxidation of NADH during fatty acid -oxidation caused a decrease in cell viability of AKD321 to H₂O₂ stress, while the 746 ⁰ mutant had no such effect. Intracellular H₂O₂ concentration increased approximately fourfold in MDH3 overexpressing ald5 strain (MD3-AKD321), compared with AKD321. The peroxisomal catalase activity of MD3-AKD321 decreased by 83% to that of AKD321. And also, the overexpression of MDH3 had only a weak effect in MDH3 overexpressing 746 ⁰ strain, decreasing by 14% to that of 746 ⁰ mutant. The increased palmitoyl CoA oxidation by overexpression of MDH3 gene was the same in both strains. Under conditions of MDH3 overexpression, peroxisomal catalase (CTA1) appears to be a limiting factor to oxidative stress. These observations point to an important, as yet unidentified, role of mitochondrial aldehyde dehydrogenase (ALD5) to endogeneous oxidative stress in peroxisome.Received: 23 September 2002 / Accepted: 24 October 2002     

Oxidation of Methanol and Formaldehyde by a System Containing Alcohol Oxidase and Catalase Purified from Candida sp. N-16

The oxidation of methanol and formaldehyde was investigated by using some combination systems of alcohol oxidase, catalase, which were purified from Candida N-16, and hydrogen peroxide. The activity of alcohol oxidase was irreversibly inhibited when the enzyme was incubated with 2.5 mm hydrogen peroxide for 15 min. However, the oxidation of methanol to formaldehyde by alcohol oxidase in the presence of catalase was extremely promoted by the addition of 30 mm hydrogen peroxide. Alcohol oxidase could oxidize not only methanol but also formaldehyde as follows: HCHO + 0₂ + H₂O→HCOOH + H₂O₂. The formaldehyde oxidizing activity was inhibited by hydrogen peroxide. The system containing alcohol oxidase and catalase appears to be the entity of the oxygen-dependent oxidation system of formaldehyde previously found in the cell-free extract of the yeast.     

Oxidative stress response in eukaryotes: effect of glutathione,superoxide dismutase and catalase on adaptation to peroxide and menadione stresses in Saccharomyces cerevisiae

Abstract

Aiming to clarify the mechanisms by which eukaryotes acquire tolerance to oxidative stress, adaptive and cross-protection responses to oxidants were investigated in Saccharomyces cerevisiae. Cells treated with sub-lethal concentrations of menadione (a source of superoxide anions) exhibited cross-protection against lethal doses of peroxide; however, cells treated with H₂O₂ did not acquire tolerance to a menadione stress, indicating that menadione response encompasses H₂O₂ adaptation. Although, deficiency in cytoplasmic superoxide dismutase (Sod1) had not interfered with response to superoxide, cells deficient in glutathione (GSH) synthesis were not able to acquire tolerance to H₂O₂ when pretreated with menadione. These results suggest that GSH is an inducible part of the superoxide adaptive stress response, which correlates with a decrease in the levels of intracellular oxidation. On the other hand, neither the deficiency of Sod1 nor in GSH impaired the process of acquisition of tolerance to H₂O₂ achieved by a mild pretreatment with peroxide. Using a strain deficient in the cytosolic catalase, we were able to conclude that the reduction in lipid peroxidation levels produced by the adaptive treatment with H₂O₂ was dependent on this enzyme. Corroborating these results, the pretreatment with low concentrations of H₂O₂ promoted an increase in catalase activity.     

Effects of hydrogen peroxide on the motility, catalase and superoxide dismutase of dam and/or seqA mutant of Salmonella typhimurium

In addition to their role in the virulence attenuation of Salmonella and other pathogens, dam or seqA genes increase the sensitivity towards hydrogen peroxide. The aim of our study is to investigate the effect of H₂O₂ on the motility, the catalase and superoxide dismutase activities of dam and/or seqA mutants of Salmonella typhimurium. Our findings showed significant differences of the effects of H₂O₂ on the motility between wild type strain and all of mutants. Hydrogen peroxide changes SOD isoenzyme profile of these mutants by disappearance of Fe-SOD. Concerning the catalase, an increase of its activity was observed in the wild type, dam and seqA mutant. However, H₂O₂ decreases the activity of this enzyme in the double mutant strain. We can suggest that the dam gene, together with seqA, play a protective role in the oxidative stress response of Salmonella typhimurium.     

Microbial adaptation to hydrogen peroxide and biodegradation of aromatic hydrocarbons

This research investigated microbial responses to bioremediation with hydrogen peroxide (H₂O₂) as a supplemental oxygen source. Columns containing aquifer material from Traverse City, MI, USA, were continuously supplied with benzene, toluene, ethylbenzene, o-xylene and m-xylene (BTEX) and H₂O₂ in increasing concentration. The microbial responses studied were changes in microbial numbers, community structure, degradative ability, and activity of catalase and superoxide dismutase (SOD). Both adaptation to H₂O₂ and stress-related consequences were observed. Adaptation to H₂O₂ was demonstrated by increased catalase and SOD activity during the course of the experiment. The microbial community in the untreated aquifer material used in the columns consisted primarily of Corynebacterium sp and Pseudomonas fluorescens. Following amendment with 500 mg L⁻¹ H₂O₂, the column inlet was dominated by P. fluorescens with few Corynebacterium sp present; Xanthomonas maltophilia dominated the middle and outlet sections. Dimethyl phenols detected in the effluent of two of the biologically active columns were probably metabolic products. The ratio of oxygen to BTEX mass consumed was approximately 0.3 before H₂O₂ addition, 0.7 following 10 mg L⁻¹ H₂O₂ supplementation, and 2.6 over the course of the experiment. Abiotic decomposition H₂O₂ was observed in a sterile column and impeded flow at a feed concentration of 500 mg L⁻¹ H₂O₂. Increasing the BTEX concentration supplied to the biologically active columns eliminated flow disruptions by satisfying the carbon and energy demand of the oxygen evolved by increasing catalase activity. Received 15 February 1996/ Accepted in revised form 15 July 1996     

Low concentration of exogenous abscisic acid increases lead tolerance in rice seedlings

The effects of exogenous abscisic acid (ABA) on lead tolerance in rice (Oryza sativa L.) seedlings were investigated. Pre-treatment with 0.1 g m³ ABA for 2 d restricted amount of Pb translocated from roots to shoots, decreased malondialdehyde and H₂O₂ contents in leaves, and alleviated Pb-induced decrease in plant growth and leaf chlorophyll content. Further, ABA pre-treatment adjusted leaf antioxidative enzyme activities (increased ascorbate peroxidase and catalase activities while decreased superoxide dismutase activity) and so alleviated oxidative stress.     

Hydroxamate-activated peroxidases in potato tuber callus. Interaction with the determination of the cytochrome and the alternative pathways

In potato (Solatium tuberosum L. cv. Bintje and Doré) callus a very active hydrox-amate-stimulated NADH-dependent O₂-uptake develops during the growth of the callus, which is caused by a peroxidase. More than 95% of the peroxidase activity is found in the 40000 g supernatant. The total activity may be as high as 1000 times the respiratory acitivity of the callus tissue. At least two fractions, obtained by Sephadex gel filtration, can be distinguished showing this peroxidase activity, one of about 15 kDa and one > 50 kDa. The main properties of both fractions are: a) Hydroxamate at 0.2–0.5 mM gives half-maximal stimulation. Maximal stimulation is observed with 1–3 mM benzhydroxamate (BHAM) and 1–15 mM salicylhydroxamate (SHAM). Higher concentrations, especially of BHAM, give less or no stimulation. b) Hydroxamates are not consumed during the reaction. c) Both NADH and NADPH can serve as the electron donor for the reaction. The affinity for NAD(P)H is very low (K_m near 10 mM). In the absence of hydroxamates NAD(P)H is only slowly oxidized, with an even lower affinity. d) The peroxidase can carry out two reactions: an O₂-consuming and a H₂O₂-consuming reaction. In both reactions one NAD(P)H is consumed. In the first reaction H₂O₂ is formed which can be consumed in the second reaction, resulting in an overall stoichiometry of 2 NADH consumed for each O₂ molecule and in the production of H₂O. e) The reaction is completely blocked by cyanide, superoxide dismutase (EC 1.15.1.1) and (excess) catalase (EC 1.11.1.6), but not by antimycin A or azide. This peroxidase-mediated O₂-uptake might interfere with respiratory measurements. In experiments with isolated mitochondria this interference can be prevented by the addition of catalase to the reaction mixture. The use of high concentrations of hydroxamate is not allowed because of inhibitory effects on the cytochrome pathway. In intact callus tissue hydroxamates only stimulate O₂-uptake in the presence of exogenous NADH. In vivo the peroxidase does not appear to function in O₂-uptake, probably because of its localization (at least partly in the cell wall) and/or its low affinity for NADH. The use of hydroxamates in the determination of cytochrome and alternative pathway activity is discussed.     

Effects of light and hydrogen peroxide on gene expression of newly identified antioxidant enzymes in the harmful algal bloom species Chattonella marina

ABSTRACT

Antioxidant enzymes are essential proteins that maintain cell proliferation potential by protecting against oxidative stress. They are present in many organisms including harmful algal bloom (HAB) species. We previously identified the antioxidant enzyme 2-Cys peroxiredoxin (PRX) in the raphidophyte Chattonella marina. This enzyme specifically decomposes a hydrogen peroxide (H₂O₂). PRX is the only antioxidant enzyme so far identified in C. marina. This study used mRNA-seq, using Trinity assemble and blastx for annotation, to identify a further five antioxidant enzymes from C. marina: Cu Zn superoxide dismutase (Cu/Zn-SOD), glutathione peroxidase (GPX), catalase (CAT), ascorbate peroxidase (APX) and thioredoxin (TRX). In the gene expression analysis of six enzymes (Cu/Zn-SOD, GPX, CAT, APX, TRX and PRX) using light-acclimated (100 μmol photons m^?2 s^?1) C. marina cells, only PRX gene expression levels were significantly increased by strong light irradiation (1000 μmol photons m^?2 s^?1). H₂O₂ concentration and scavenging activity were also increased and significantly positively correlated with PRX gene expression levels. In dark-acclimated cells, expression levels of all antioxidant enzymes except APX were significantly increased by light irradiation (100 μmol photons m^?2 s^?1). Expression decreased the following day, with the exception of PRX expression. With the exception of CAT, gene expression of antioxidant enzymes was not significantly induced by artificial H₂O₂ treatment, although average gene expression levels were slightly increased in some enzymes. Thus, we suggest that light is the main trigger of gene expression, but the resultant oxidative stress is also a possible factor affecting the gene expression of antioxidant enzymes in C. marina.     

Effect of hydrogen peroxide on antioxidant enzyme activities in Saccharomyces cerevisiae is strain-specific

The effect of hydrogen peroxide on the survival and activity of antioxidant and associated enzymes in Saccharomyces cerevisiae has been studied. A difference found in the response of wild-type yeast strains treated with hydrogen peroxide was probably related to the different protective effects of antioxidant enzymes in these strains. Exposure of wild-type YPH250 cells to 0.25 mM H₂O₂ for 30 min increased activities of catalase and superoxide dismutase (SOD) by 3.4-and 2-fold, respectively. However, no activation of catalase in the EG103 strain, as well as of SOD in the YPH98 and EG103 wild strains was detected, which was in parallel to lower survival of these strains under oxidative stress. There is a strong positive correlation (R ² = 0.95) between activities of catalase and SOD in YPH250 cells treated with different concentrations of hydrogen peroxide. It is conceivable that catalase would protect SOD against inactivation caused by oxidative stress and vice versa. Finally, yeast cell treatment with hydrogen peroxide can lead to either a H₂O₂-induced increase in activities of antioxidant and associated enzymes or their decrease depending on the H₂O₂ concentration used or the yeast strain specificity. Published in Russion in Biokhimiya, 2006, Vol. 71, No. 9, pp. 1243–1252.