Understanding the structure and function of catalases: clues from molecular evolution and in vitro mutagenesis

Guedes HL, Nosanchuk JD, Zancopé-Oliveira RM. Biological function and molecular mapping of M antigen in yeast phase of Histoplasma capsulatum

Histoplasmosis, due to the intracellular fungus Histoplasma capsulatum, can be diagnosed by demonstrating the presence of antibodies specific to the immunodominant M antigen. However, the role of this protein in the pathogenesis of histoplasmosis has not been elucidated. We sought to structurally and immunologically characterize the protein, determine yeast cell surface expression, and confirm catalase activity. A 3D-rendering of the M antigen by homology modeling revealed that the structures and domains closely resemble characterized fungal catalases. We generated monoclonal antibodies (mAbs) to the protein and determined that the M antigen is present on the yeast cell surface and in cell wall/cell membrane preparations. Similarly, we found that the majority of catalase activity was in extracts containing fungal surface antigens and that the M antigen is not significantly secreted by live yeast cells. The mAbs also identified unique epitopes on the M antigen. The localization of the M antigen to the cell surface of H. capsulatum yeast and the characterization of the protein's major epitopes have important implications since it demonstrates that although the protein may participate in protecting the fungus against oxidative stress it is also accessible to host immune cells and antibody.

A Note Concerning Acetate Activation of Peroxidative Activity of Catalases Using 2,2′-Azino-bis(3-ethylbenzthiazoline)-6-sulfonic Acid as a Substrate

Beef liver catalases showed peroxidative activity using 2,2'-azino-bis-(3-ethylbenzthiazoline)-6-sulfonic acid as the electron donor and hydrogen peroxide as the acceptor at a pH of 5. This activity was not observed at pH 7. The reaction depended on acetate concentration, although succinate and propionate could partly replace the acetate as a catalyst. Other haem proteins also catalyzed a peroxidative effect. The reaction using syringaldazine or the coupling between dimethylaminobenzoic acid and 3-methyl-2-benzothiazolinone hydrazone was less effective and less sensitive. Evidence is presented that the reaction is associated with a conformational change of the catalase.

Evolution of catalases from bacteria to humans

Excessive hydrogen peroxide is harmful for almost all cell components, so its rapid and efficient removal is of essential importance for aerobically living organisms. Conversely, hydrogen peroxide acts as a second messenger in signal-transduction pathways. H(2)O(2) is degraded by peroxidases and catalases, the latter being able both to reduce H(2)O(2) to water and to oxidize it to molecular oxygen. Nature has evolved three protein families that are able to catalyze this dismutation at reasonable rates. Two of the protein families are heme enzymes: typical catalases and catalase-peroxidases. Typical catalases comprise the most abundant group found in Eubacteria, Archaeabacteria, Protista, Fungi, Plantae, and Animalia, whereas catalase-peroxidases are not found in plants and animals and exhibit both catalatic and peroxidatic activities. The third group is a minor bacterial protein family with a dimanganese active site called manganese catalases. Although catalyzing the same reaction (2 H(2)O(2)--> 2 H(2)O+ O(2)), the three groups differ significantly in their overall and active-site architecture and the mechanism of reaction. Here, we present an overview of the distribution, phylogeny, structure, and function of these enzymes. Additionally, we report about their physiologic role, response to oxidative stress, and about diseases related to catalase deficiency in humans.

On the functional role of a water molecule in clade 3 catalases: a proposal for the mechanism by which NADPH prevents the formation of compound II

X-ray structures of the 13 different monofunctional heme catalases published to date were scrutinized in order to gain insight in the mechanism by which NADPH in Clade 3 catalases may protect the reactive ferryloxo intermediate Compound I (Cpd I; por (*+)Fe (IV)O) against deactivation to the catalytically inactive intermediate Compound II (Cpd II; porFe (IV)O). Striking similarities in the molecular network of the protein subunits encompassing the heme center and the surface-bound NADPH were found for all of the Clade 3 catalases. Unique features in this region are the presence of a water molecule (W1) adjacent to the 4-vinyl group of heme and a serine residue or a second water molecule hydrogen-bonded to both W1 and the carbonyl group of a threonine-proline linkage, with the proline in van der Waals contact with the dihydronicotinamide group of NADPH. A mechanism is proposed in which a hydroxyl anion released from W1 undergoes reversible nucleophilic addition to the terminal carbon of the 4-vinyl group of Cpd I, thereby producing a neutral porphyrin pi-radical ferryloxo (HO-por (*)Fe (IV)O) species of reduced reactivity. This structure is suggested to be the elusive Cpd II' intermediate proposed in previous studies. An accompanying proton-shifting process along the hydrogen-bonded network is believed to facilitate the NADPH-mediated reduction of Cpd I to ferricatalase and to serve as a funnel for electron transfer from NADPH to the heme center to restore the catalase Fe (III) resting state. The proposed reaction paths were fully supported as chemically reasonable and energetically feasible by means of density functional theory calculations at the (U)B3LYP/6-31G* level. A particularly attractive feature of the present mechanism is that the previously discussed formation of protein-derived radicals is avoided.

Partial characterization and expression of leaf catalase in the CAM-inducible halophyte Mesembryanthemum crystallinum L

Catalase (CAT; EC 1.11.1.6) isolated from leaves of the halophytic plant Mesembryanthemum crystallinum is characterized by a high apparent molecular mass of about 320kDa, and high resistance to denaturing agents (10% ME). SDS-treatment breaks active oligomeric CAT into the less active and putatively dimeric form of 160kDa apparent molecular mass. Three subunits are resolved after denaturing PAGE: 79, 74 and 62kDa. Higher molecular masses of subunits coincide with increased activity of CAT. M. crystallinum leaf CAT reveals a diel variation in the resistance to denaturing factors and the stability of CAT is increased in a light-dependent manner both in C(3)- and in CAM-induced plants. Unchanged level of leaf CAT transcripts is documented in the diurnal cycle of C(3) plants and after salinity-induced crassulacean acid metabolism (CAM).

Purification, characterization, and identification of a novel bifunctional catalase-phenol oxidase from Scytalidium thermophilum

A novel bifunctional catalase with an additional phenol oxidase activity was isolated from a thermophilic fungus, Scytalidium thermophilum. This extracellular enzyme was purified ca. 10-fold with 46% yield and was biochemically characterized. The enzyme contains heme and has a molecular weight of 320 kDa with four 80 kDa subunits and an isoelectric point of 5.0. Catalase and phenol oxidase activities were most stable at pH 7.0. The activation energies of catalase and phenol oxidase activities of the enzyme were found to be 2.7 +/- 0.2 and 10.1 +/- 0.4 kcal/mol, respectively. The pure enzyme can oxidize o-diphenols such as catechol, caffeic acid, and L-DOPA in the absence of hydrogen peroxide and the highest oxidase activity is observed against catechol. No activity is detected against tyrosine and common laccase substrates such as ABTS and syringaldazine with the exception of weak activity with p-hydroquinone. Common catechol oxidase inhibitors, salicylhydroxamic acid and p-coumaric acid, inhibit the oxidase activity. Catechol oxidation activity was also detected in three other catalases tested, from Aspergillus niger, human erythrocyte, and bovine liver, suggesting that this dual catalase-phenol oxidase activity may be a common feature of catalases.

Helicobacter hepaticus catalase shares surface-predicted epitopes with mammalian catalases

Helicobacter hepaticus colonizes the murine intestine and has been associated with hepatic inflammation and neoplasia in susceptible mouse strains. In this study, the catalase of an enterohepatic Helicobacter was characterized for the first time. H. hepaticus catalase is a highly conserved enzyme that may be important for bacterial survival in the mammalian intestine. Recombinant H. hepaticus catalase was expressed in Escherichia coli in order to verify its enzymic activity in vitro. H. hepaticus catalase comprises 478 amino acids with a highly conserved haem-ligand domain. Three conserved motifs (R-F-Y-D, RERIPER and VVHAKG) in the haem-ligand domain and three surface-predicted motifs were identified in H. hepaticus catalase and are shared among bacterial and mammalian catalases. H. hepaticus catalase is present in the cytoplasmic and periplasmic compartments. Mice infected with H. hepaticus demonstrated immune responses to murine and H. hepaticus catalase, suggesting that Helicobacter catalase contains conserved structural motifs and may contribute to autoimmune responses. Antibodies to H. hepaticus catalase recognized murine hepatocyte catalase in hepatic tissue from infected mice. Antibodies from sera of H. hepaticus-infected mice reacted with peptides comprising two conserved surface-predicted motifs in H. hepaticus catalase. Catalases are highly conserved enzymes in bacteria and mammals that may contribute to autoimmune responses in animals infected with catalase-producing pathogens.

Molecular identification and properties of a light-insensitive rice catalase-B expressed in E. coli

Catalase plays a central role in plant stress responses but is highly susceptible to photoinhibition. A rice catalase-B protein avoiding photoinhibition was developed by mutagenesis of specific amino acids: Leu-189 to Trp-189 and His-225 to Thr-225 and then recombinantly expressed in E. coli. In addition, the site specific mutation also induced 2-2.5-fold increase in enzyme velocity with high affinity for its substrate and showed nearly a 3-fold lower K(m) than the wild protein. These characteristic of mutated rice catalase-B is highly promising in transgenic research to increase plant productivity under stress conditions.

Oxidative stress, glucose metabolism, and the prevention of type 2 diabetes: pathophysiological insights

With the rising epidemic of type 2 diabetes worldwide, including the United States, the death and disability due to the suboptimal control of cardiovascular disease associated with this epidemic has made prevention of type 2 diabetes emerge as a primary strategic intervention. Several modalities have been assessed in large randomized controlled trials for diabetes prevention such as lifestyle interventions and various pharmacologic agents. Included in these agents are metformin, thiazolidinediones, acarbose, angiotensin converting enzyme inhibitors, as well as angiotensin receptor blockers. Abrogation of oxidative stress appears to be a common soil hypothesis that explains the favorable effects of these agents on glucose metabolism, including the prevention of diabetes and its complications. This comprehensive review highlights the role of oxidative stress in the pathogenesis of diabetes, with emphasis on the major clinical trials conducted on prevention of type 2 diabetes.

Hydrogen Peroxide Decomposition by a Non-Heme Iron(III) Catalase Mimic: A DFT Study

Non-heme iron(III) complexes of 14-membered tetraaza macrocycles have previously been found to catalytically decompose hydrogen peroxide to water and molecular oxygen, like the native enzyme catalase. Here the mechanism of this reaction is theoretically investigated by DFT calculations at the (U)B3LYP/6-31G* level, with focus on the reactivity of the possible spin states of the FeIII complexes. The computations suggest that H2O2 decomposition follows a homolytic route with intermediate formation of an iron(IV) oxo radical cation species (L.+FeIV==O) that resembles Compound I of natural iron porphyrin systems. Along the whole catalytic cycle, no significant energetic differences were found for the reaction proceeding on the doublet (S=1/2) or on the quartet (S=3/2) hypersurface, with the single exception of the rate-determining O--O bond cleavage of the first associated hydrogen peroxide molecule, for which reaction via the doublet state is preferred. The sextet (S=5/2) state of the FeIII complexes appears to be unreactive in catalase-like reactions.

The structures and electronic configuration of compound I intermediates of Helicobacter pylori and Penicillium vitale catalases determined by X-ray crystallography and QM/MM density functional theory calculations

The structures of Helicobacter pylori (HPC) and Penicillium vitale (PVC) catalases, each with two subunits in the crystal asymmetric unit, oxidized with peroxoacetic acid are reported at 1.8 and 1.7 A resolution, respectively. Despite the similar oxidation conditions employed, the iron-oxygen coordination length is 1.72 A for PVC, close to what is expected for a Fe=O double bond, and 1.80 and 1.85 A for HPC, suggestive of a Fe-O single bond. The structure and electronic configuration of the oxoferryl heme and immediate protein environment is investigated further by QM/MM density functional theory calculations. Four different active site electronic configurations are considered, Por*+-FeIV=O, Por*+-FeIV=O...HisH+, Por*+-FeIV-OH+ and Por-FeIV-OH (a protein radical is assumed in the latter configuration). The electronic structure of the primary oxidized species, Por*+-FeIV=O, differs qualitatively between HPC and PVC with an A2u-like porphyrin radical delocalized on the porphyrin in HPC and a mixed A1u-like "fluctuating" radical partially delocalized over the essential distal histidine, the porphyrin, and, to a lesser extent, the proximal tyrosine residue. This difference is rationalized in terms of HPC containing heme b and PVC containing heme d. It is concluded that compound I of PVC contains an oxoferryl Por*+-FeIV=O species with partial protonation of the distal histidine and compound I of HPC contains a hydroxoferryl Por-FeIV-OH with the second oxidation equivalent delocalized as a protein radical. The findings support the idea that there is a relation between radical migration to the protein and protonation of the oxoferryl bond in catalase.

Mammalian catalase: a venerable enzyme with new mysteries

Mammalian catalase has been the subject of many classic biochemical studies. Despite our detailed knowledge of its functional mechanisms and its three-dimensional structure, however, several unexpected features of mammalian catalase have been recently discovered. For example, some mammalian catalases seem to have oxidase activity and produce reactive oxygen species when exposed to UVB light. In addition, bovine catalase uses unbound NAD(P)H to prevent substrate inactivation without displacing catalase-bound NADP(+). Coupled with the earlier discovery of catalase-bound NADPH, these developments indicate that serendipity and new investigative approaches can reveal unexpected features, even for an enzyme that has been studied for over 100 years.

Degradation of phenolic compounds with hydrogen peroxide catalyzed by enzyme from Serratia marcescens AB 90027

In this paper, the degradation of phenolic compounds using hydrogen peroxide as oxidizer and the enzyme extract from Serratia marcescens AB 90027 as catalyst was reported. With such an enzyme/H2O2 combination treatment, a high chemical oxygen demand (COD) removal efficiency was achieved, e.g., degradation of hydroquinone exceeded 96%. From UV-visible and IR spectra, the degradation mechanisms were judged as a process of phenyl ring cleavage. HPLC analysis shows that in the degradation p-benzoquinone, maleic acid and oxalic acid were formed as intermediates and that they were ultimately converted to CO2 and H2O. With the enzyme/H2O2 treatment, vanillin, hydroquinone, catechol, o-aminophenol, p-aminophenol, phloroglucinol and p-hydroxybenzaldehyde were readily degraded, whereas the degradation of phenol, salicylic acid, resorcinol, p-cholorophenol and p-nitrophenol were limited. Their degradability was closely related to the properties and positions of their side chain groups. Electron-donating groups, such as -OH, -NH2 and -OCH3 enhanced the degradation, whereas electron-withdrawing groups, such as -NO2, -Cl and -COOH, had a negative effect on the degradation of these compounds in the presence of enzyme/H2O2. Compounds with -OH at ortho and para positions were more readily degraded than those with -OH at meta positions.

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.

Iron(II) and hydrogen peroxide detoxification by human H-chain ferritin. An EPR spin-trapping study

Overexpression of human H-chain ferritin (HuHF) is known to impart a degree of protection to cells against oxidative stress and the associated damage to DNA and other cellular components. However, whether this protective activity resides in the protein's ability to inhibit Fenton chemistry as found for Dps proteins has never been established. Such inhibition does not occur with the related mitochondrial ferritin which displays much of the same iron chemistry as HuHF, including an Fe(II)/H(2)O(2) oxidation stoichiometry of approximately 2:1. In the present study, the ability of HuHF to attenuate hydroxyl radical production by the Fenton reaction (Fe(2+) + H(2)O(2) --> Fe(3+) + OH(-) + *OH) was examined by electron paramagnetic resonance (EPR) spin-trapping methods. The data demonstrate that the presence of wild-type HuHF during Fe(2+) oxidation by H(2)O(2) greatly decreases the amount of .OH radical produced from Fenton chemistry whereas the ferroxidase site mutant 222 (H62K + H65G) and human L-chain ferritin (HuLF) lack this activity. HuHF catalyzes the pairwise oxidation of Fe(2+) by the detoxification reaction [2Fe(2+) + H(2)O(2) + 2H(2)O --> 2Fe(O)OH(core) + 4H(+)] that occurs at the ferroxidase site of the protein, thereby preventing the production of hydroxyl radical. The small amount of *OH radical that is produced in the presence of ferritin (<or=1% of the iron oxidized) appears to arise from the reaction of H(2)O(2) with Fe(III) in the protein rather than from simple Fenton chemistry. The results are discussed in terms of recent experiments reporting both protective and degradative effects of ferritin iron on the integrity of nuclear DNA.

Cold adapted features of Vibrio salmonicida catalase: characterisation and comparison to the mesophilic counterpart from Proteus mirabilis

The gene encoding catalase from the psychrophilic marine bacterium Vibrio salmonicida LFI1238 was identified, cloned and expressed in the catalase-deficient Escherichia coli UM2. Recombinant catalase from V. salmonicida (VSC) was purified to apparent homogeneity as a tetramer with a molecular mass of 235 kDa. VSC contained 67% heme b and 25% protoporphyrin IX. VSC was able to bind NADPH, react with cyanide and form compounds I and II as other monofunctional small subunit heme catalases. Amino acid sequence alignment of VSC and catalase from the mesophilic Proteus mirabilis (PMC) revealed 71% identity. As for cold adapted enzymes in general, VSC possessed a lower temperature optimum and higher catalytic efficiency (k (cat)/K (m)) compared to PMC. VSC have higher affinity for hydrogen peroxide (apparent K (m)) at all temperatures. For VSC the turnover rate (k (cat)) is slightly lower while the catalytic efficiency is slightly higher compared to PMC over the temperature range measured, except at 4 degrees C. Moreover, the catalytic efficiency of VSC and PMC is almost temperature independent, except at 4 degrees C where PMC has a twofold lower efficiency compared to VSC. This may indicate that VSC has evolved to maintain a high efficiency at low temperatures.

Molecular identification, heterologous expression and properties of light-insensitive plant catalases

Most catalases are inactivated by light in a heme-sensitized and O2-dependent reaction. In leaves of the alpine plant Homogyne alpina and in the peroxisomal cores of Helianthus annuus, light-insensitive catalases were observed. For the catalases Hacat1 of H. alpina and HnncatA3 of H. annuus, cDNA clones were obtained. Expression of recombinant active enzymes in insect cells confirmed that they coded for light-insensitive catalases. Kinetic and catalytic properties of light-sensitive or light-insensitive catalases did not differ substantially. However, the specific activity of the latter was markedly lower. The light-insensitive catalase HaCAT-1 was not resistant against inactivation by superoxide. Amino acid sequences of the light-insensitive catalases HaCAT-1 and HNNCATA3 were highly identical. They showed only a few exceptional amino acid substitutions at positions that are highly conserved in other catalases. These appeared to be localized mainly in a surface cavity at the entrance of a minor channel leading to the central heme, suggesting that this region played some, though yet undefined, role for light sensitivity. While the replacement of a highly conserved His by Thr225 was the most unique substitution, a single exchange of His225 by Thr in the light-sensitive catalase SaCAT-1 by mutagenesis was not sufficient to reduce its sensitivity to photoinactivation.

Crystallization and preliminary X-ray diffraction analysis of a cold-adapted catalase from Vibrio salmonicida

Catalase (EC 1.11.1.6) catalyses the breakdown of hydrogen peroxide to water and molecular oxygen. Recombinant Vibrio salmonicida catalase (VSC) possesses typical cold-adapted features, with higher catalytic efficiency, lower thermal stability and a lower temperature optimum than its mesophilic counterpart from Proteus mirabilis. Crystals of VSC were produced by the hanging-drop vapour-diffusion method using ammonium sulfate as precipitant. The crystals belong to the monoclinic space group P2(1), with unit-cell parameters a = 98.15, b = 217.76, c = 99.28 A, beta = 110.48 degrees. Data were collected to 1.96 A and a molecular-replacement solution was found with eight molecules in the asymmetric unit.

Ergot alkaloids--biology and molecular biology

EA have been a major benefit, and a major detriment, to humans since early in recorded history. Their medicinal properties have been used, and continue to be used, to aid in childbirth, with new uses being found in the treatment of neurological and cardiovascular disorders. The surprisingly broad range of pharmaceutical uses for EA stems from their affinities for multiple receptors for three distinct neurotransmitters (serotonin, dopamine, and adrenaline), from the great structural diversity of natural EA, and from the application of chemical techniques that further expand that structural diversity. The dangers posed by EA to humans and their livestock stem from the ubiquity of ergot fungi (Claviceps species) as parasites of cereals, and of related grass endophytes (Epichloë, Neotyphodium, and Balansia species) that may inhabit pasture grasses and produce toxic levels of EA. Further concerns stem from saprophytic EA producers in the genera Aspergillus and Penicillium, especially A. fumigatus, an opportunistic pathogen of humans. Numerous fungal species produce EA with a wide variety of structures and properties. These alkaloids are associated with plants in the families Poaceae, Cyperaceae, and Convolvulaceae, apparently because these plants can have symbiotic fungi that produce EA. Pharmacological activities of EA relate to their specific structures. Known as potent vasoconstrictors, the ergopeptines include a lysergic acid substituent with an amide linkage to a complex cyclol-lactam ring structure generated from three amino acids. Simpler lysergyl amides and clavines are more apt to have oxytonic or psychotropic activities. One of the lysergyl amides is LSD (5), the most potent hallucinogen known. The EA biosynthetic pathway in Claviceps species has been studied extensively for many decades, and recent studies have also employed epichloës and A. fumigatus. The early pathway, shared among these fungi, begins with the action of an aromatic prenyl transferase, DMATrp synthase, which links a dimethylallyl chain to L-tryptophan. When the dmaW gene encoding DMATrp synthase was cloned and sequenced, the predicted product bore no identifiable resemblance to other known prenyl transferases. The dma W genes of Claviceps species are present in clusters of genes, several of which also have demonstrated roles in EA biosynthesis. In many other fungi, dma W homologues are identifiable in otherwise very different gene clusters. The roles of DMA Trp synthase homologues in these other fungi are probably quite variable. One of them is thought to prenylate the phenolic oxygen of L-tyrosine, and another catalyzes the unusual reverse prenylation reaction in the biosynthesis of fumigaclavine C(10), an EA characteristic of A. fumigatus. The second step of the EA pathway is N-methylation of DMATrp (12) to form 13, which is then subjected to a series of oxidation/oxygenation and reduction reactions to generate, in order, chanoclavine-I (16), agroclavine (19), and elymoclavine (6). Shunt reactions generate a wide variety of other clavines. Two epimerizations occur in this pathway: one from 12 to 16, the other from 16 to 19. Further oxidation of 6, catalyzed by the cytochrome-P450 CloA, generates lysergic acid (1). An unusual NRPS complex, lysergyl peptide synthetase (LPS), is responsible for linking 1 to three hydrophobic L-amino acids to generate the ergopeptide lactams. The LPS complex includes two polypeptides, one (LPS 2) possessing a single module for activation of 1, and the other (LPS 1) possessing three modules, each specifying one of the L-amino acids. Variations in LPS 1 sequences are associated with variations in the incorporated amino acids, leading to differences between strain chemotypes, and even multiple ergopeptines within strains. For example, C. purpurea P1 produces two distinct ergopeptines (ergotamine (4) and ergocryptine (Table I)), each of which is believed to be generated by multiple LPS 1 subunits encoded by separate, but related, genes (lpsA1 and lpsA2). The main ecological roles of EA in nature are probably to protect the fungi from consumption by vertebrate and invertebrate animals. The EA produced by plant-symbiotic fungi (such as epichloë endophytes) may protect the fungus by protecting the health and productivity of the host, which may otherwise suffer excessive grazing by animals. The EA, at levels typical of plants bearing these symbionts, can negatively affect the health of large mammals as well herbivorous insects. Some clavines have substantial anti-bacterial properties, which might protect the fungus and, in some cases, their host plants from infection. However, the fact that a large number of epichloë, and even several Claviceps species, produce no detectable EA indicates that the selection for their production is not universal. An unfortunate fact for many livestock producers is that some of the most popular forage grasses tend to possess EA-producing epichloë endophytes. Such endophytes are easily eliminated, but confer such fitness enhancements to their hosts that their presence is often preferred, despite the toxic EA. The future looks promising for continued interest in EA. Research continues into their pharmacological properties, medicinal uses, and structure-function relationships. New clavines and lysergic acid derivatives are identified regularly from new sources, such as marine animals. Also, programs are well underway to modify or replace epichloë endophytes of forage grasses in order to produce new grass cultivars that lack these toxins.

A minor catalase/peroxidase from Burkholderia cenocepacia is required for normal aconitase activity

The opportunistic bacterium Burkholderia cenocepacia C5424 contains two catalase/peroxidase genes, katA and katB. To investigate the functions of these genes, katA and katB mutants were generated by targeted integration of suicide plasmids into the katA and katB genes. The catalase/peroxidase activity of the katA mutant was not affected as compared with that of the parental strain, while no catalase/peroxidase activity was detected in the katB mutant. However, the katA mutant displayed reduced resistance to hydrogen peroxide under iron limitation, while the katB mutant showed hypersensitivity to hydrogen peroxide, and reduced growth under all conditions tested. The katA mutant displayed reduced growth only in the presence of carbon sources that are metabolized through the tricarboxylic acid (TCA) cycle, as the growth defect was abrogated in cultures supplemented with glucose or glycerol. This phenotype was also correlated with a marked reduction in aconitase activity. In contrast, aconitase activity was not reduced in the katB mutant and parental strains. The authors conclude that the KatA protein is a specialized catalase/peroxidase that has a novel function by contributing to maintain the normal activity of the TCA cycle, while KatB is a classical catalase/peroxidase that plays a global role in cellular protection against oxidative stress.

Characterization of the Oxidase Activity in Mammalian Catalase

Catalase is a highly conserved heme-containing antioxidant enzyme known for its ability to degrade hydrogen peroxide into water and oxygen. In low concentrations of hydrogen peroxide, the enzyme also exhibits peroxidase activity. We report that mammalian catalase also possesses oxidase activity. This activity, which is detected in purified catalases, cell lysates, and intact cells, requires oxygen and utilizes electron donor substrates in the absence of hydrogen peroxide or any added cofactors. Using purified bovine catalase and 10-acetyl-3,7-dihydroxyphenoxazine as the substrate, the oxidase activity was found to be temperature-dependent and displays a pH optimum of 7-9. The Km for the substrate is 2.4 x 10(-4) m, and Vmax is 4.7 x 10(-5) m/s. Endogenous substrates, including the tryptophan precursor indole, the neurotransmitter precursor beta-phenylethylamine, and a variety of peroxidase and laccase substrates, as well as carcinogenic benzidines, were found to be oxidized by catalase or to inhibit this activity. Several dietary plant micronutrients that inhibit carcinogenesis, including indole-3-carbinol, indole-3-carboxaldehyde, ferulic acid, vanillic acid, and epigallocatechin-3-gallate, were effective inhibitors of the activity of catalase oxidase. Difference spectroscopy revealed that catalase oxidase/substrate interactions involve the heme-iron; the resulting spectra show time-dependent decreases in the ferric heme of the enzyme with corresponding increases in the formation of an oxyferryl intermediate, potentially reflecting a compound II-like intermediate. These data suggest a mechanism of oxidase activity involving the formation of an oxygen-bound, substrate-facilitated reductive intermediate. Our results describe a novel function for catalase potentially important in metabolism of endogenous substrates and in the action of carcinogens and chemopreventative agents.

(salen)MnIII compounds as nonpeptidyl mimics of catalase. Mechanism-based tuning of catalase activity: a theoretical study

We present the results of the first theoretical investigation of salen-manganese complexes as synthetic catalytic scavengers of hydrogen peroxide molecules that mimic catalase enzymes. Catalase mimics can be used as therapeutic agents against oxidative stress in treatment of many diseases, including Alzheimer's disease, stroke, heart disease, aging, and cancer. A ping-pong mechanism approach has been considered to describe the H2O2 dismutation reaction. The real compounds reacting with a peroxide molecule were utilized in our BP density functional calculations to avoid uncertainties connected with using incomplete models. Part I of the dismutation reaction-converting a peroxide molecule into a water molecule with simultaneous oxidation of the metal atom of the catalyst-can be done quite effectively at the Mn catalytic center. To act as catalytic scavengers of hydrogen peroxide, the oxomanganese salen complexes have to be deoxidized during part II of the dismutation reaction. It has been shown that there are two possible reaction routes for the second part of the dismutation reaction: the top and the side substrate approach routes. Our results suggest that the catalyst could be at least temporarily deactivated (poisoned) in the side approach reaction route due to the formation of a kinetically stable intermediate. Overall, the side approach reaction route for the catalyst recovery is the bottleneck for the whole dismutation process. On the basis of the detailed knowledge of the mode of action of the (salen)MnIII catalase mimics, we suggest and rationalize structural changes of the catalyst that should lead to better therapeutic properties. The available experimental data support our conclusions. Our findings on the reaction dismutation mechanism could be the starting point for further improvement of salen-manganese complexes as synthetic catalytic scavengers of reactive oxygen species.

Catalase from the silkworm, Bombyx mori: gene sequence, distribution, and overexpression

Living organisms require mechanisms regulating reactive oxygen species (ROS) such as hydrogen peroxide and superoxide anion. Catalase is one of the regulatory enzymes and facilitates the degradation of hydrogen peroxide to oxygen and water. Biochemical information on an insect catalase is, however, insufficient. Using mRNA from fat body of the silkworm, Bombyx mori, a cDNA encoding a putative catalase was amplified by reverse transcriptase-polymerase chain reaction and sequenced. The deduced amino acid sequence comprised 507 residues with more than seventy residues forming a scaffold for a heme cofactor conserved. The sequence showed 71% and 66% identities to those of the Drosophila melanogaster and Apis mellifera catalases, respectively; the catalase from B. mori was estimated to be phylogenetically close to that from A. mellifera. The transcripts of the gene and the catalase activity were distributed in diverse tissues of B. mori, suggesting its ubiquitous nature. Using the gene, a recombinant catalase (rCAT) was functionally overexpressed in a soluble form using Escherichia coli, purified to homogeneity, and characterized. The pH-optimum of rCAT was broad around pH 8.0. More than 80% of the original rCAT activity was retained after incubation in the following conditions: at pH 8-11 and 4 degrees C for 24 h; at pH 7 and temperatures below 50 degrees C for 30 min. The Michaelis constant for hydrogen peroxide was evaluated to be 28 mM at pH 6.5 and 30 degrees C. rCAT was suggested to be a member of the typical catalase family.

Use of an antisense RNA strategy to investigate the functional significance of Mn-catalase in the extreme thermophile Thermus thermophilus

The expression of an antisense RNA revealed that an Mn-catalase was required in Thermus thermophilus for aerobic but not for anaerobic growth. The antisense system is based on the constitutive expression of a "bicistronic" transcript consisting of the kanamycin resistance gene mRNA followed by the antisense RNA against the selected target.

Microbial detoxification of superoxide: the non-heme iron reductive paradigm for combating oxidative stress

A reductive paradigm has emerged in recent years for detoxification of superoxide and other redox active diatomic molecules in air-sensitive bacteria and archaea. Adventitiously generated superoxide in many anaerobic or microaerophilic bacteria and archaea is scavenged by superoxide reductase (SOR) rather than the classical superoxide dismutases characteristic of aerobic microbes. SORs contain a novel five-coordinate, square-pyramidal [Fe(His)4(Cys)] ferrous active site, which adds a sixth glutamate ligand upon oxidation. This Account summarizes the recently elucidated structural and mechanistic features of SORs. The non-heme iron reductive scavenging paradigm in these air-sensitive microbes also extends to recently characterized enzymes that scavenge hydrogen peroxide and nitric oxide and to oxygen sensing proteins.

Unusual Cys-Tyr covalent bond in a large catalase

Catalase-1, one of four catalase activities of Neurospora crassa, is associated with non-growing cells and accumulates in asexual spores. It is a large, tetrameric, highly efficient, and durable enzyme that is active even at molar concentrations of hydrogen peroxide. Catalase-1 is oxidized at the heme by singlet oxygen without significant effects on enzyme activity. Here we present the crystal structure of catalase-1 at 1.75A resolution. Compared to structures of other catalases of the large class, the main differences were found at the carboxy-terminal domain. The heme group is rotated 180 degrees around the alpha-gamma-meso carbon axis with respect to clade 3 small catalases. There is no co-ordination bond of the ferric ion at the heme distal side in catalase-1. The catalase-1 structure exhibited partial oxidation of heme b to heme d. Singlet oxygen, produced catalytically or by photosensitization, may hydroxylate C5 and C6 of pyrrole ring III with a subsequent formation of a gamma-spirolactone in C6. The modification site in catalases depends on the way dioxygen exits the protein: mainly through the central channel or the main channel in large and small catalases, respectively. The catalase-1 structure revealed an unusual covalent bond between a cysteine sulphur atom and the essential tyrosine residue of the proximal side of the active site. A peptide with the predicted theoretical mass of the two bound tryptic peptides was detected by mass spectrometry. A mechanism for the Cys-Tyr covalent bond formation is proposed. The tyrosine bound to the cysteine residue would be less prone to donate electrons to compound I to form compound II, explaining catalase-1 resistance to substrate inhibition and inactivation. An apparent constriction of the main channel at Ser198 lead us to propose a gate that opens the narrow part of the channel when there is sufficient hydrogen peroxide in the small cavity before the gate. This mechanism would explain the increase in catalytic velocity as the hydrogen peroxide concentration rises.

Phylogenetic relationships in class I of the superfamily of bacterial, fungal, and plant peroxidases

Molecular phylogeny among catalase-peroxidases, cytochrome c peroxidases, and ascorbate peroxidases was analysed. Sixty representative sequences covering all known subgroups of class I of the superfamily of bacterial, fungal, and plant heme peroxidases were selected. Each sequence analysed contained the typical peroxidase motifs evolved to bind effectively the prosthetic heme group, enabling peroxidatic activity. The N-terminal and C-terminal domains of catalase-peroxidases matching the ancestral tandem gene duplication event were treated separately in the phylogenetic analysis to reveal their specific evolutionary history. The inferred unrooted phylogenetic tree obtained by three different methods revealed the existence of four clearly separated clades (C-terminal and N-terminal domains of catalase-peroxidases, ascorbate peroxidases, and cytochrome c peroxidases) which were segregated early in the evolution of this superfamily. From the results, it is obvious that the duplication event in the gene for catalase-peroxidase occurred in the later phase of evolution, in which the individual specificities of the peroxidase families distinguished were already formed. Evidence is presented that class I of the heme peroxidase superfamily is spread among prokaryotes and eukaryotes, obeying the birth-and-death process of multigene family evolution.

Mechanism of H2O2 Dismutation Catalyzed by a New Catalase Mimic (a Non-Heme Dibenzotetraaza[14]annulene−Fe(III) Complex): A Density Functional Theory Investigation

The mechanism of H(2)O(2) dismutation catalyzed by the dibenzotetraaza[14]annulene-Fe(III) complex ([Fe(C(24)H(22)N(4)O(4))](+)) which was recently reported (Paschke, J.; Kirsch, M.; Korth, H. G.; de Groot, H.; Sustmann, R. J. Am. Chem. Soc. 2001, 123, 11099) has been investigated by density functional theory using the B3LYP hybrid functional. The quartet potential energy profile of the catalytic reaction has been explored. In the whole catalytic cycle, the rate-determining step is found to be the O-O bond homolytic cleavage, without the assistance of solvent molecules in the second coordination shell. The calculated free energy barrier for this step is 10.8 kcal/mol, which is in reasonable agreement with the experimental facts. The calculations also show that the hydroxyl and hydroperoxyl radicals may be generated in the reaction processes, but they can be efficiently quenched in strongly exothermic steps. This study provides a satisfactory explanation to the observed efficiency of the H(2)O(2) dismutation catalyzed by this complex.

A perspective on mechanisms of protein tetramer formation

Homotetrameric proteins can assemble by several different pathways, but have only been observed to use one, in which two monomers associate to form a homodimer, and then two homodimers associate to form a homotetramer. To determine why this pathway should be so uniformly dominant, we have modeled the kinetics of tetramerization for the possible pathways as a function of the rate constants for each step. We have found that competition with the other pathways, in which homotetramers can be formed either by the association of two different types of homodimers or by the successive addition of monomers to homodimers and homotrimers, can cause substantial amounts of protein to be trapped as intermediates of the assembly pathway. We propose that this could lead to undesirable consequences for an organism, and that selective pressure may have caused homotetrameric proteins to evolve to assemble by a single pathway.

Expression, purification, and sequence analysis of catalase-1 from the soil bacterium Comamonas terrigena N3H

Catalases are essential components of the cellular equipment to cope with oxidative stress. We have purified and characterize herein the most abundant heme-containing catalase-1 from the soil bacterium Comamonas terrigena N3H. This oxidative stress-induced enzyme was isolated from exponential phase cells grown in the presence of peroxyacetic acid. We have used consecutive steps of hydrophobic, molecular sieve, and ion exchange chromatography to achieve a high state of purity for this metalloenzyme. The purified sample of catalase exhibited a specific catalytic activity of 55,900 U/mg, allosteric behavior in peroxidic reaction, a broad pH optimum, and a rather atypical electronic spectrum. The sample of highest purity was subjected to mass spectrometry analysis. The molecular weight of the subunit of this homodimeric protein was determined as 55,417 Da. The Qq-TOF mass analysis method allowed us to sequence short tryptic fragments of this catalase. Five such fragments with a total length of 57 amino acids together with several enzymatic properties allowed the classification of this hydroperoxidase as belonging to clade III of monofunctional catalases. The highest sequence similarity is with the catalase from Vibrio fischeri. The presented results imply the significance of this inducible enzyme in the prevention of toxic effects of oxidative stress for bacterial cells.

Catalytic Activity for Decomposition of Hydrogen Peroxide by Metal Complexes of Water-Soluble Thiacalix[4]arenetetrasulfonate on the Modified Anion-Exchangers

The catalytic activity for the decomposition of hydrogen peroxide by anion-exchangers modified with metal complexes of thiacalix[4]arenetetrasulfonate (Me(n+)-TCAS[4], Me(n+)=Mn(3+), Mn(2+), Fe(3+), Co(3+), Co(2+), Cu(2+), Zn(2+) and Ni(2+)) was investigated. As a reference, calix[4]arenetetrasulfonate, calix[6]arenehexasulfonate and calix[8]areneoctasulfonate were also examined. Mn(3+)- and Fe(3+)-TCAS[4] on the modified anion-exchangers showed high catalytic activity in alkaline buffer solutions among metal complexes tested. Mn(3+)- and Fe(3+)-TCAS[4] on the modified anion-exchangers exhibited high and constant levels of catalytic activity even after having been used 5 times, and showed catalytic activity in the presence of an excess of H(2)O(2) over Mn(3+)- and Fe(3+)-TCAS[4] on the modified anion-exchangers. Only Mn(3+)-TCAS[4] on the modified anion-exchangers exhibited high catalytic activity at around a neutral pH.

Catalase activity in human healthy and inflamed dental pulps

AIM

To examine the catalase activity in clinically healthy and symptomatic human dental pulps to verify if an active defence system against oxidizing agents is present as a response to bacterial invasion.

METHODOLOGY

Thirty-three systemically healthy patients, 18 females and 15 males (ages: 11.0-25.9 years; mean 18.8 +/- 3.6), were the source of the pulp tissue. The condition of the pulps was assessed using clinical and radiographic evaluations. The specimens were recovered by longitudinally grooving and splitting the teeth (if extracted) or during endodontic treatment, and were matched for age and sex between the healthy and inflamed specimen groups. Catalase activity was determined through spectrophotometric methods.

RESULTS

Enzymatic activity was 1126 +/- 343 and 3074 +/- 698 mU mL(-1) x mg of total protein in the healthy and inflamed pulp tissue specimens, respectively. This difference was statistically significant (P<0.01).

CONCLUSIONS

These results indicate a role for catalase during dental pulp inflammation in humans, and may represent an inherent biological defence system against reactive oxidants of this tissue.

Influence of vitamin C diet supplementation on endogenous antioxidant defences during exhaustive exercise

We determined the effects of dietary vitamin C supplementation on erythrocyte antioxidant enzymes and on plasma antioxidants during athletic competition and short-term recovery. Blood samples were taken from 16 volunteer endurance athletes, participating in a duathlon competition, under basal conditions and both immediately and 1 h after the competition. The results were analysed taking into account the individual vitamin C intake and the plasma levels. Athletes were assigned to either the vitamin C-supplemented or control groups ( n=8 each). The control group had normal plasma ascorbate levels, the supplemented group high levels as a result of the higher vitamin C intake. Uric acid and lactate dehydrogenase increased after the competition only in the control group. Plasma ascorbate decreased after short-term recovery in the supplemented group. Erythrocyte catalase activity increased after the competition in the supplemented group. Glutathione peroxidase activity (determined with cumene hydroperoxide as substrate) increased only in the control group after short-term recovery. This pattern may suggest an important role for plasma ascorbate, and dietary vitamin C supplementation, in the defence against oxidative stress induced by exercise and in avoiding negative effects on erythrocyte integrity.

The Dictyostelium discoideum prespore-specific catalase B functions to control late development and to protect spore viability

Changes in the levels of reactive oxygen species (ROS) have been associated previously with cell differentiation and development in several systems. Thus, there is interest in studying the developmental regulation of antioxidant enzymes, whose activities may modulate ROS levels and subsequent oxidant-mediated signal transduction events in specific tissues. Our recent identification in Dictyostelium discoideum of the prespore-specific catalase B (CatB) enzyme suggested (a) that the CatB enzyme functions to provide protection to the mature spores, and (b) that the CatB enzyme may have a regulatory role in cell differentiation and morphogenesis. We have now confirmed both these hypotheses. We specifically disrupted the catB gene by homologous recombination. The resulting catB null strain displays a 4-h delay in development at the time of normal catB gene expression, followed by slow and asynchronous development of fruiting bodies, taking 10 h longer than the isogenic parent strain. The expression of both prestalk- and prespore-specific genes was altered in the mutant both temporally and quantitatively, and the resultant mutant spores had increased sensitivity to H(2)O(2). This study supports the idea that CatB functions in the development of D. discoideum by regulating the level of ROS, and adds to the growing body of evidence for regulatory roles for ROS.