Enzymology and structure of catalases. Advances in Inorganic Chemistry Volume 51. Elsevier; 2000. pp. 51-106. [DOI: 10.1016/s0898-8838(00)51001-0]

High dietary fat selectively increases catalase expression within cardiac mitochondria

Obesity is a predictor of diabetes and cardiovascular disease. One consequence of obesity is dyslipidemia characterized by high blood triglycerides. It has been proposed that oxidative stress, driven by utilization of lipids for energy, contributes to these diseases. The effects of oxidative stress are mitigated by an endogenous antioxidant enzyme network, but little is known about its response to high fat utilization. Our experiments used a multiplexed quantitative proteomics method to measure antioxidant enzyme expression in heart tissue in a mouse model of diet-induced obesity. This experiment showed a rapid and specific up-regulation of catalase protein, with subsequent assays showing increases in activity and mRNA. Catalase, traditionally considered a peroxisomal protein, was found to be present in cardiac mitochondria and significantly increased in content and activity during high fat feeding. These data, coupled with the fact that fatty acid oxidation enhances mitochondrial H(2)O(2) production, suggest that a localized catalase increase is needed to consume excessive mitochondrial H(2)O(2) produced by increased fat metabolism. To determine whether the catalase-specific response is a common feature of physiological conditions that increase blood triglycerides and fatty acid oxidation, we measured changes in antioxidant expression in fasted versus fed mice. Indeed, a similar specific catalase increase was observed in mice fasted for 24 h. Our findings suggest a fundamental metabolic process in which catalase expression is regulated to prevent damage while preserving an H(2)O(2)-mediated sensing of diet composition that appropriately adjusts insulin sensitivity in the short term as needed to prioritize lipid metabolism for complete utilization.

Ascorbic acid reduction of compound I of mammalian catalases proceeds via specific binding to the NADPH binding pocket

Mammalian (Clade 3) catalases utilize NADPH as a protective cofactor to prevent one-electron reduction of the central reactive intermediate Compound I (Cpd I) to the catalytically inactive Compound II (Cpd II) species by re-reduction of Cpd I to the enzyme's resting state (ferricatalase). It has long been known that ascorbate/ascorbic acid is capable of reducing Cpd I of NADPH-binding catalases to Cpd II, but the mode of this one-electron reduction had hitherto not been explored. We here demonstrate that ascorbate-mediated reduction of Cpd I, generated by addition of peroxoacetic acid to NADPH-free bovine liver catalase (BLC), requires specific binding of the ascorbate anion to the NADPH binding pocket. Ascorbate-mediated Cpd II formation was found to be suppressed by added NADPH in a concentration-dependent manner, for the achievement of complete suppression at a stoichiometric 1:1 NADPH:heme concentration ratio. Cpd I → Cpd II reduction by ascorbate was similarly inhibited by addition of NADH, NADP(+), thio-NADP(+), or NAD(+), though with 0.5-, 0.1-, 0.1-, and 0.01-fold reduced efficiencies, respectively, in agreement with the relative binding affinities of these dinucleotides. Unexpected was the observation that although Cpd II formation is not observed in the presence of NADP(+), the decay of Cpd I is slightly accelerated by ascorbate rather than retarded, leading to direct regeneration of ferricatalase. The experimental findings are supported by molecular mechanics docking computations, which show a similar binding of NADPH, NADP(+), and NADH, but not NAD(+), as found in the X-ray structure of NADPH-loaded human erythrocyte catalase. The computations suggest that two ascorbate molecules may occupy the empty NADPH pocket, preferably binding to the adenine binding site. The biological relevance of these findings is discussed.

Cytochrome P450-type hydroxylation and epoxidation in a tyrosine-liganded hemoprotein, catalase-related allene oxide synthase

The ability of hemoproteins to catalyze epoxidation or hydroxylation reactions is usually associated with a cysteine as the proximal ligand to the heme, as in cytochrome P450 or nitric oxide synthase. Catalase-related allene oxide synthase (cAOS) from the coral Plexaura homomalla, like catalase itself, has tyrosine as the proximal heme ligand. Its natural reaction is to convert 8R-hydroperoxy-eicosatetraenoic acid (8R-HPETE) to an allene epoxide, a reaction activated by the ferric heme, forming product via the Fe(IV)-OH intermediate, Compound II. Here we oxidized cAOS to Compound I (Fe(V)=O) using the oxygen donor iodosylbenzene and investigated the catalytic competence of the enzyme. 8R-hydroxyeicosatetraenoic acid (8R-HETE), the hydroxy analog of the natural substrate, normally unreactive with cAOS, was thereby epoxidized stereospecifically on the 9,10 double bond to form 8R-hydroxy-9R,10R-trans-epoxy-eicosa-5Z,11Z,14Z-trienoic acid as the predominant product; the turnover was 1/s using 100 μm iodosylbenzene. The enantiomer, 8S-HETE, was epoxidized stereospecifically, although with less regiospecificity, and was hydroxylated on the 13- and 16-carbons. Arachidonic acid was converted to two major products, 8R-HETE and 8R,9S-eicosatrienoic acid (8R,9S-EET), plus other chiral monoepoxides and bis-allylic 10S-HETE. Linoleic acid was epoxidized, whereas stearic acid was not metabolized. We conclude that when cAOS is charged with an oxygen donor, it can act as a stereospecific monooxygenase. Our results indicate that in the tyrosine-liganded cAOS, a catalase-related hemoprotein in which a polyunsaturated fatty acid can enter the active site, the enzyme has the potential to mimic the activities of typical P450 epoxygenases and some capabilities of P450 hydroxylases.

The reaction mechanisms of heme catalases: an atomistic view by ab initio molecular dynamics

Catalases are ubiquitous enzymes that prevent cell oxidative damage by degrading hydrogen peroxide to water and oxygen (2H(2)O(2) → 2H(2)O+O(2)) with high efficiency. The enzyme is first oxidized to a high-valent iron intermediate, known as Compound I (Cpd I, Por(·+)-Fe(IV)=O) which, at difference from other hydroperoxidases, is reduced back to the resting state by further reacting with H(2)O(2). The normal catalase activity is reduced if Cpd I is consumed in a competing side reaction, forming a species named Cpd I*. In recent years, Density Functional Theory (DFT) methods have unraveled the electronic configuration of these high-valent iron species, helping to assign the intermediates trapped in the crystal structures of oxidized catalases. It has been demonstrated that the a priori assumption that the H(+)/H(-) type of mechanism for Cpd I reduction leads to the generation of singlet oxygen is not justified. Moreover, it has been shown by ab initio metadynamics simulations that two pathways are operative for Cpd I reduction: a His-mediated mechanism (described as H·/H(+) + e(-)) in which the distal His acts as an acid-base catalyst and a direct mechanism (described as H·/H·) in which the distal His does not play a direct role. Independently of the mechanism, the reaction proceeds by two one-electron transfers rather than one two-electron transfer, as previously assumed. Electron transfer to Cpd I, regardless of whether the electron is exogenous or endogenous, facilitates protonation of the oxoferryl group, to the point that formation of Cpd I* may be controlled by the easiness of protonation of reduced Cpd I.

Classical catalase: ancient and modern

This review describes the historical difficulties in devising a kinetically satisfactory mechanism for the classical catalase after its identification as a unique catalytic entity in 1902 and prior to the breakthrough 1947 analysis by Chance and co-workers which led to the identification of peroxide compounds I and II. The role of protons in the formation of these two ferryl complexes is discussed and current problems of inhibitory ligand and hydrogen donor binding at the active site are outlined, especially the multiple roles involving formate or formic acid. A previous mechanism of NADPH-dependent catalase protection against substrate inhibition is defended. A revised model linking the catalytic ('catalatic') action and the one-electron side reactions involving compound II is suggested. And it is concluded that, contrary to an idea proposed in 1963 that eukaryotic catalase might be a 'fossil enzyme', current thinking gives it a central role in the redox protective processes of long term importance for human and other eukaryotic and prokaryotic life.

Spectroscopic studies of peroxo/hydroperoxo derivatives of heme proteins and model compounds

The spectroscopic characterization of peroxo- and hydroperoxo- intermediates of heme proteins and enzymes has long interested scientists studying the structure and function of these important biochemical systems. Until very recently, little progress had been made in studying these fleeting intermediates by vibrational spectroscopic methods. In this brief review, recent studies reporting the Resonance Raman and Infrared spectra of such intermediates and pertinent model compounds are reviewed and compared to corresponding studies utilizing electronic absorption and electron paramagnetic resonance spectrometric methods.

Expression and purification of soluble bio-active rice plant catalase-A from recombinant Escherichia coli

Catalase in plants is a heme-coordinated tetrameric protein that primarily disproportionates hydrogen peroxide into water and oxygen. It plays an important role in maintaining cellular concentration of hydrogen peroxide to a level, necessary for all aspects of normal plant growth and development. Except for its recombinant expression in transgenic plants and insect cell line, the protein is yet to be synthesized in its bio-active form in prokaryotic expression system. Attempts made in past for recombinant expression of plant catalase in Escherichia coli consistently resulted in formation of insoluble and inactive aggregates of inclusion body. Here we have shown the specific requirement of a thioredoxin fusion partner, the involvement of trigger factor protein and the low temperature treatment during induction period for synthesis of completely solubilized rice plant catalase-A in recombinant E. coli. Furthermore, the bacteria required the supplementation of δ-aminolevulinic acid to produce bio-active recombinant rice catalase-A. The molecular and biochemical properties of the purified recombinant protein showed the characteristic features of a typical mono-functional plant catalase. These results attest to the usefulness of the present protocol for production of plant catalase using E. coli as heterologous expression system.

Polyelectrolyte complex optimization for macrophage delivery of redox enzyme nanoparticles

BACKGROUND

We posit that cell-mediated drug delivery can improve transport of therapeutic enzymes to the brain and decrease inflammation and neurodegeneration seen during Parkinson's disease. Our prior works demonstrated that macrophages loaded with nanoformulated catalase ('nanozyme') then parenterally injected protect the nigrostriatum in a murine model of Parkinson's disease. Packaging of catalase into block ionomer complex with a synthetic polyelectrolyte block copolymer precludes enzyme degradation in macrophages.

METHODS

We examined relationships between the composition and structure of block ionomer complexes with a range of block copolymers, their physicochemical characteristics, and loading, release and catalase enzymatic activity in bone marrow-derived macrophages.

RESULTS

Formation of block ionomer complexes resulted in improved aggregation stability. Block ionomer complexes with ε-polylysine and poly(L-glutamic acid)-poly(ethylene glycol) demonstrated the least cytotoxicity and high loading and release rates. However, these formulations did not efficiently protect catalase inside macrophages.

CONCLUSION

Nanozymes with polyethyleneimine- and poly(L-lysine)(10)-poly(ethylene glycol) provided the best protection of enzymatic activity for cell-mediated drug delivery.

ABA controls H₂O₂ accumulation through the induction of OsCATB in rice leaves under water stress

The production of both ABA and H₂O₂ is induced by drought and can act as signals under stress conditions. We investigated the relationships between ABA, H₂O₂ and catalase (CAT) in rice leaves when rice seedlings were treated with polyethylene glycol as water stress treatment. As a key gene in ABA biosynthesis, OsNCED3 was significantly induced in rice by water stress treatment and such induction preceded the rapid increase in ABA. Water stress inhibited the expression of CATA and CATC but substantially enhanced the expression of CATB. Exogenously applied ABA promoted the expression of CATB also and inhibited the expression of CATC in a concentration-dependent manner. When ABA production was inhibited by using ABA biosynthesis inhibitors nordihydroguaiaretic acid and tungstate, expression of CATB was also subdued while CATC was enhanced under the water stress. Accumulation of H₂O₂ was also reduced when endogenous ABA production was inhibited and showed a correlation with the total activity of catalases. Our results suggest that water stress-induced ABA prevents the excessive accumulation of H₂O₂, through the induction of the expression of CATB gene during water stress.

Ethyl gallate, a scavenger of hydrogen peroxide that inhibits lysozyme-induced hydrogen peroxide signaling in vitro, reverses hypotension in canine septic shock

Although hydrogen peroxide (H2O2) is a well-described reactive oxygen species that is known for its cytotoxic effects and associated tissue injury, H2O2 has recently been established as an important signaling molecule. We previously demonstrated that lysozyme (Lzm-S), a mediator of sepsis that is released from leukocytes, could produce vasodilation in a phenylephrine-constricted carotid artery preparation by H2O2 signaling. We found that Lzm-S could intrinsically generate H2O2 and that this generation activated H2O2-dependent pathways. In the present study, we used this carotid artery preparation as a bioassay to define those antioxidants that could inhibit Lzm-S's vasodilatory effect. We then determined whether this antioxidant could reverse the hypotension that developed in an Escherichia coli bacteremic model. Of the many antioxidants tested, we found that ethyl gallate (EG), a nonflavonoid phenolic compound, was favorable in inhibiting Lzm-S-induced vasodilation. In our E. coli model, we found that EG reversed the hypotension that developed in this model and attenuated end-organ dysfunction. By fluorometric H2O2 assay and electrochemical probe techniques, we showed that EG could scavenge H2O2 and that it could reduce H2O2 production in model systems. These results show that EG, an antioxidant that was found to scavenge H2O2 in vitro, was able to attenuate cardiovascular dysfunction in a canine in vivo preparation. Antioxidants such as EG may be useful in the treatment of hemodynamic deterioration in septic shock.

Human catalase: looking for complete identity

Catalases are well studied enzymes that play critical roles in protecting cells against the toxic effects of hydrogen peroxide. The ubiquity of the enzyme and the availability of substrates made heme catalases the focus of many biochemical and molecular biology studies over 100 years. In human, this has been implicated in various physiological and pathological conditions. Advancement in proteomics revealed many of novel and previously unknown features of this mysterious enzyme, but some functional aspects are yet to be explained. Along with discussion on future research area, this mini-review compile the information available on the structure, function and mechanism of action of human catalase.

The dynamic role of distal side residues in heme hydroperoxidase catalysis. Interplay between X-ray crystallography and ab initio MD simulations

The enzymatic cycle of hydroperoxidases involves the resting Fe(III) state of the enzyme and the high-valent iron intermediates Compound I and Compound II. These states might be characterized by X-ray crystallography and the transition pathways between each state can be investigated using atomistic simulations. Here we review our recent work in the modeling of two key steps of the enzymatic reaction of hydroperoxidases: the formation of Cpd I in peroxidase and the reduction of Cpd I in catalase. It will be shown that small conformational motions of distal side residues (His in peroxidases and His/Asn in catalases), not,or only partially, revealed by the available X-ray structures, play an important role in the catalytic processes examined.

B3LYP study on reduction mechanisms from O2 to H2O at the catalytic sites of fully reduced and mixed-valence bovine cytochrome c oxidases

Reduction mechanisms of oxygen molecule to water molecules in the fully reduced (FR) and mixed-valence (MV) bovine cytochrome c oxidases (CcO) have been systematically examined based on the B3LYP calculations. The catalytic cycle using four electrons and four protons has been also shown consistently. The MV CcO catalyses reduction to produce one water molecule, while the FR CcO catalyses to produce two water molecules. One water molecule is added into vacant space between His240 and His290 in the catalytic site. This water molecule constructs the network of hydrogen bonds of Tyr244, farnesyl ethyl, and Thr316 that is a terminal residue of the K-pathway. It plays crucial roles for the proton transfer to the dioxygen to produce the water molecules in both MV and FR CcOs. Tyr244 functions as a relay of the proton transfer from the K-pathway to the added water molecule, not as donors of a proton and an electron to the dioxygen. The reduction mechanisms of MV and FR CcOs are strictly distinguished. In the FR CcO, the Cu atom at the Cu(B) site maintains the reduced state Cu(I) during the process of formation of first water molecule and plays an electron storage. At the final stage of formation of first water molecule, the Cu(I) atom releases an electron to Fe-O. During the process of formation of second water molecule, the Cu atom maintains the oxidized state Cu(II). In contrast with experimental proposals, the K-pathway functions for formation of first water molecule, while the D-pathway functions for second water molecule. The intermediates, P(M), P(R), F, and O, obtained in this work are compared with those proposed experimentally.

Retracted Article: On the enzymatic activity of catalase: an iron L-edge X-ray absorption study of the active centre

Fe L_2,3-edge X-ray absorption spectra of a catalase active centre in a physiological solution reveals a partial ferryl character, which stems from the proximal tyrosine residue.

The effect of intracellular delivery of catalase and antisense oligonucleotides to NF-kappaB using albumin microcapsules in the endotoxic shock model

Microencapsulated (MC) catalase has been shown to inhibit H(2)O(2) and tumor necrosis factor (TNF) in vitro after endotoxin stimulation. It is the purpose of this study to determine whether MC catalase improves pro-inflammatory cytokine inhibition and mortality in an endotoxic shock model in vivo. We also examined whether MC catalase and antisense oligonucleotides (ASO) to nuclear factor kappaB (NF-kappaB) together improved survival by inhibiting pro-inflammatory cytokines using different mechanisms.

METHODS

Albumin microcapsules containing catalase and ASO to NF-kappaB were prepared 2-7 microm in size by using a Büchi spray dryer. Progressively increasing doses of MC catalase, MC ASO to NF-kappaB, and the combination were given to rats before the administration of Escherichia coli endotoxin. Results demonstrated 60% survival in rats given 15 mg/kg MC catalase, 70% survival with 20 mg/kg MC ASO NF-kappaB, and 80% survival with the combination. TNF was inhibited by 53% in the MC catalase group 4 h after endotoxin administration, 43% in the ASO NF-kappaB group, and 78% in the combination group compared to controls. In conclusion, this study demonstrates the effectiveness of MC intracellular delivery of the naturally occurring antioxidant catalase in improving animal survival. The addition of ASO to NF-kappaB improved both cytokine inhibition and animal survival in endotoxic shock.

Catalytic scavenging of peroxynitrite by catalase

Peroxynitrite (ONOO(-)/ONOOH), the product of the diffusion controlled reaction between nitric oxide (*NO) and superoxide anion (O(2)(-)*), is a strong oxidizing and nitrating agent. Several heme proteins react rapidly with peroxynitrite, some of them catalyze its decomposition. In this work we found, contrary to previous reports, that catalase, a ferriheme enzyme, catalytically scavenges peroxynitrite. The second-order reaction rate constants of peroxynitrite decay catalyzed by catalase increase with decreasing pH and are equal to (2.7+/-0.2) x 10(6), (1.7+/-0.1) x 10(6) and (0.8+/-0.1) x 10(6) M(-1) s(-1) at pH 6.1, 7.1 and 8.0, respectively. This dependence suggests that peroxynitrous acid, ONOOH, is the species that reacts with heme center of catalase. The possible reaction mechanisms of the decay of peroxynitrite catalyzed by catalase and physiological relevance of this reaction are discussed.

The influence of X-rays on the structural studies of peroxide-derived myoglobin intermediates

In recent years, the awareness of potential radiation damage of metal centers in protein crystals during crystallographic data collection has received increasing attention. The radiation damage can lead to radiation-induced changes and reduction of the metal sites. One of the research fields where these concerns have been comprehensively addressed is the study of the reaction intermediates of the heme peroxidase and oxygenase reaction cycles. For both the resting states and the high-valent intermediates, the X-rays used in the structure determination have given undesired side effects through radiation-induced changes to the trapped intermediates. However, X-rays have been used to generate and trap the peroxy/hydroperoxy state in crystals. In this review, the structural work and the influence of X-rays on these intermediates in myoglobin are summarized and viewed in light of analogous studies on similar intermediates in peroxidases and oxygenases.

Catalase-peroxidase activity of iron(III)-TAML activators of hydrogen peroxide

Exceptionally high peroxidase-like and catalase-like activities of iron(III)-TAML activators of H 2O 2 ( 1: Tetra-Amidato-Macrocyclic-Ligand Fe (III) complexes [ F e{1,2-X 2C 6H 2-4,5-( NCOCMe 2 NCO) 2CR 2}(OH 2)] (-)) are reported from pH 6-12.4 and 25-45 degrees C. Oxidation of the cyclometalated 2-phenylpyridine organometallic complex, [Ru (II)( o-C 6H 4py)(phen) 2]PF 6 ( 2) or "ruthenium dye", occurs via the equation [ Ru II ] + 1/2 H 2 O 2 + H +-->(Fe III - TAML) [ Ru III ] + H 2 O, following a simple rate law rate = k obs (per)[ 1][H 2O 2], that is, the rate is independent of the concentration of 2 at all pHs and temperatures studied. The kinetics of the catalase-like activity (H 2 O 2 -->(Fe III - TAML) H 2 O + 1/2 O 2) obeys a similar rate law: rate = k obs (cat)[ 1][H 2O 2]). The rate constants, k obs (per) and k obs (cat), are strongly and similarly pH dependent, with a maximum around pH 10. Both bell-shaped pH profiles are quantitatively accounted for in terms of a common mechanism based on the known speciation of 1 and H 2O 2 in this pH range. Complexes 1 exist as axial diaqua species [FeL(H 2O) 2] (-) ( 1 aqua) which are deprotonated to afford [FeL(OH)(H 2O)] (2-) ( 1 OH) at pH 9-10. The pathways 1 aqua + H 2O 2 ( k 1), 1 OH + H 2O 2 ( k 2), and 1 OH + HO 2 (-) ( k 4) afford one or more oxidized Fe-TAML species that further rapidly oxidize the dye (peroxidase-like activity) or a second H 2O 2 molecule (catalase-like activity). This mechanism is supported by the observations that (i) the catalase-like activity of 1 is controllably retarded by addition of reducing agents into solution and (ii) second order kinetics in H 2O 2 has been observed when the rate of O 2 evolution was monitored in the presence of added reducing agents. The performances of the 1 complexes in catalyzing H 2O 2 oxidations are shown to compare favorably with the peroxidases further establishing Fe (III)-TAML activators as miniaturized enzyme replicas with the potential to greatly expand the technological utility of hydrogen peroxide.

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.

Role of the conserved distal heme asparagine of coral allene oxide synthase (Asn137) and human catalase (Asn148): mutations affect the rate but not the essential chemistry of the enzymatic transformations

A catalase-related allene oxide synthase (cAOS) and true catalases that metabolize hydrogen peroxide have similar structure around the heme. One of the distal heme residues considered to help control catalysis is a highly conserved asparagine. Here we addressed the role of this residue in metabolism of the natural substrate 8R-hydroperoxyeicosatetraenoic acid by cAOS and in H(2)O(2) breakdown by catalase. In cAOS, the mutations N137A, N137Q, N137S, N137D, and N137H drastically reduced the rate of reaction (to 0.8-4% of wild-type), yet the mutants all formed the allene oxide as product. This is remarkable because there are many potential heme-catalyzed transformations of fatty acid hydroperoxides and special enzymatic control must be required. In human catalase, the N148A, N148S, or N148D mutations only reduced rates to approximately 20% of wild-type. The distal heme Asn is not essential in either catalase or cAOS. Its conservation throughout evolution may relate to a role in optimizing catalysis.

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.

The potential of Angeli's salt to decrease nitric oxide scavenging by plasma hemoglobin

Release of hemoglobin from the erythrocyte during intravascular hemolysis contributes to the pathology of a variety of diseased states. This effect is partially due to the enhanced ability of cell-free plasma hemoglobin, which is primarily found in the ferrous, oxygenated state, to scavenge nitric oxide. Oxidation of the cell-free hemoglobin to methemoglobin, which does not effectively scavenge nitric oxide, using inhaled nitric oxide has been shown to be effective in limiting pulmonary and systemic vasoconstriction. However, the ferric heme species may be reduced back to ferrous hemoglobin in plasma and has the potential to drive injurious redox chemistry. We propose that compounds that selectively convert cell-free hemoglobin to ferric, and ideally iron-nitrosylated heme species that do not actively scavenge nitric oxide, would effectively treat intravascular hemolysis. We show here that nitroxyl generated by Angeli's salt (sodium alpha-oxyhyponitrite, Na2N2O3) preferentially reacts with cell-free hemoglobin compared to that encapsulated in the red blood cell under physiologically relevant conditions. Nitroxyl oxidizes oxygenated ferrous hemoglobin to methemoglobin and can convert the methemoglobin to a more stable, less toxic species, iron-nitrosyl hemoglobin. These results support the notion that Angeli's salt or a similar compound could be used to effectively treat conditions associated with intravascular hemolysis.

Protecting peroxidase activity of multilayer enzyme-polyion films using outer catalase layers

Films constructed layer-by-layer on electrodes with architecture {protein/hyaluronic acid (HA)}n containing myoglobin (Mb) or horseradish peroxidase (HRP) were protected against protein damage by H2O2 by using outer catalase layers. Peroxidase activity for substrate oxidation requires activation by H2O2, but {protein/HA}n films without outer catalase layers are damaged slowly and irreversibly by H2O2. The rate and extent of damage were decreased dramatically by adding outer catalase layers to decompose H2O2. Comparative studies suggest that protection results from catalase decomposing a fraction of the H2O2 as it enters the film, rather than by an in-film diffusion barrier. The outer catalase layers controlled the rate of H2O2 entry into inner regions of the film, and they biased the system to favor electrocatalytic peroxide reduction over enzyme damage. Catalase-protected {protein/HA}n films had an increased linear concentration range for H2O2 detection. This approach offers an effective way to protect biosensors from damage by H2O2.

Potential role of thiol:disulfide oxidoreductases in the pathogenesis ofHelicobacter pylori

Helicobacter pylori infections are responsible for a sequence of molecular events which ultimately result in the development of gastric diseases. The pathogenesis of H. pylori has been studied extensively with strong focus on the identification of virulence factors. In contrast, the involvement of thiol:disulfide oxidoreductases in bacterial pathogenesis is less well understood. This paper provides a review of the current knowledge of H. pylori putative thiol:disulfide oxidoreductases, and their potential role in promoting virulence and colonization. Several bioinformatic analyses served to complete the information on these oxidoreductases of H. pylori.

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.

Phylogenetic distribution of catalase-peroxidases: are there patches of order in chaos?

Hydrogen peroxide features in many biological oxidative processes and must be continuously degraded enzymatically either via a catalatic or a peroxidatic mechanism. For this purpose ancestral bacteria evolved a battery of different heme and non-heme enzymes, among which heme-containing catalase-peroxidases (CP) are one of the most widespread representatives. They are unique since they can follow both H(2)O(2)-degrading mechanisms, the catalase activity being clearly dominant. With the fast increasing amount of genomic data available, we were able to perform an extensive search for CP and found almost 300 sequences covering a large range of microorganisms. Most of them were encoded by bacterial genomes, but we could also find some in eukaryotic organisms other than fungi, which has never been shown until now. Our screen also reveals that approximately 60% of the bacteria do not possess CP genes. Chaotic distribution among species and incongruous phylogenetic reconstruction indicated existence of numerous lateral gene transfers in addition to duplication events and regular speciation. The results obtained show an impressively complex gene transmission pattern, and give some new insights about the role of CP and the origin of life on earth. Finally, we propose for the first time bacterial candidates that may have participated in the transfer of CP from bacteria to eukaryotes.

Catalases of Aspergillus fumigatus and inflammation in aspergillosis

The article describes various features of aspergillosis and a discussed the role of calatases produced by Aspergillus fumigatus during infection. Since a large body of invasive Aspergillus infection occurs as an opportunistic infection in variously impaired defense mechanisms, there is a wide spectrum of histopathological features of lesions demonstrated at the site of infection. Accordingly, histopathology of the lesions can be understood as a phenotypical representation of interaction between differently impaired functions of neutrophils and macrophages and virulence factors of invading Aspergilli. Consideration of previous pathological knowledge regarding infection and inflammation provides much important information to predict the pathophysiology of a patient. Meanwhile, detoxification of hydrogen peroxide by catalases has been proposed as a way to overcome this host response. A. fumigatus produces three active catalases, one from conidia and two from mycelia. CatAp, a spore specific monofunctional catalase, is resistant to heat and metal ions. In spite of their increased sensitivity to H(2)O(2), killing of catA conidia by alveolar macrophages, virulence in animals was similar to wild type conidia. In contrast to mycelial Cat1p, and CatAp catalases, the mycelial Cat2p is a bifunctional catalase-peroxidase enzyme and is also sensitive to heat, metal ions and detergent. Surprisingly, the mycelium of the double cat1 cat2 mutant with no catalase activity has only a slightly increased sensitivity to H(2)O(2) and was as sensitive to the killing of polymorphonuclear neutrophils as the wild type strain. However, it showed a delayed infection in the rat model of aspergillosis compared to the wild type strain. Consequently, it should be emphasized that conidial catalase is not a virulence factor but that mycelial catalases transiently protect the fungus from the host defence reactions.

Spectroscopic description of an unusual protonated ferryl species in the catalase from Proteus mirabilis and density functional theory calculations on related models. Consequences for the ferryl protonation state in catalase, peroxidase and chloroperoxidase

The catalase from Proteus mirabilis peroxide-resistant bacteria is one of the most efficient heme-containing catalases. It forms a relatively stable compound II. We were able to prepare samples of compound II from P. mirabilis catalase enriched in (57)Fe and to study them by spectroscopic methods. Two different forms of compound II, namely, low-pH compound II (LpH II) and high-pH compound II (HpH II), have been characterized by Mössbauer, extended X-ray absorption fine structure (EXAFS) and UV-vis absorption spectroscopies. The proportions of the two forms are pH-dependent and the pH conversion between HpH II and LpH II is irreversible. Considering (1) the Mössbauer parameters evaluated for four related models by density functional theory methods, (2) the existence of two different Fe-O(ferryl) bond lengths (1.80 and 1.66 A) compatible with our EXAFS data and (3) the pH dependence of the alpha band to beta band intensity ratio in the absorption spectra, we attribute the LpH II compound to a protonated ferryl Fe(IV)-OH complex (Fe-O approximately 1.80 A), whereas the HpH II compound corresponds to the classic ferryl Fe(IV)=O complex (Fe=O approximately 1.66 A). The large quadrupole splitting value of LpH II (measured 2.29 mm s(-1) vs. computed 2.15 mm s(-1)) compared with that of HpH II (measured 1.47 mm s(-1) vs. computed 1.46 mm s(-1)) reflects the protonation of the ferryl group. The relevancy and involvement of such (Fe(IV)=O/Fe(IV)-OH) species in the reactivity of catalase, peroxidase and chloroperoxidase are discussed.

Structure, protonation state and dynamics of catalase compound II

Density functional calculations are performed to investigate the protonation state of the compound II intermediate (Cpd II) of the catalase reaction cycle. Several scenarios are considered, depending on the protonation state of the active center (heme) and the catalytic His residue. Only the form with a protonated Fe==O unit (i.e. Fe--OH) is in agreement with the recent high-resolution crystal structure, while the traditional description of Cpd II as an oxoferryl species corresponds to a configuration slightly higher in energy. The computed Fe--O stretch frequency is in agreement with the available experimental data. Molecular dynamics simulations show that the pocket water remains in the region between the His61 and Asn133 catalytic residues, but it occasionally tries to escape towards the main channel in a concerted motion with the Asn133 residue. A possible role for this residue in the process of ligand entry/escape from the binding pocket is proposed.

Hydrogen peroxide oxidation by catalase-peroxidase follows a non-scrambling mechanism

Despite catalyzing the same reaction (2 H2O2-->2 H2O+O2) heme-containing monofunctional catalases and bifunctional catalase-peroxidases (KatGs) do not share sequence or structural similarities raising the question of whether or not the reaction pathways are similar or different. The production of dioxygen from hydrogen peroxide by monofunctional catalases has been shown to be a two-step process involving the redox intermediate compound I which oxidizes H2O2 directly to O2. In order to investigate the origin of O2 released in KatG mediated H2O2 degradation we performed a gas chromatography-mass spectrometry investigation of the evolved O2 from a 50:50 mixture of H2(18)O2/H2(16)O2 solution containing KatGs from Mycobacterium tuberculosis and Synechocystis PCC 6803. The GC-MS analysis clearly demonstrated the formation of (18)O2 (m/e = 36) and (16)O2 (m/e = 32) but not (16)O(18)O (m/e = 34) in the pH range 5.6-8.5 implying that O2 is formed by two-electron oxidation without breaking the O-O bond. Also active site variants of Synechocystis KatG with very low catalase but normal or even enhanced peroxidase activity (D152S, H123E, W122F, Y249F and R439A) are shown to oxidize H2O2 by a non-scrambling mechanism. The results are discussed with respect to the catalatic mechanism of KatG.

Stereochemical control of H2O2 dismutation by Hangman porphyrins

Incorporation of a disparate set of aryl groups appended to the meso-positions of Hangman porphyrin xanthene architectures dramatically impacts the ability of such systems to catalyze the disproportionation of H2O(2)via the catalase reaction.

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.

Modification of the active site of Mycobacterium tuberculosis KatG after disruption of the Met-Tyr-Trp cross-linked adduct

Mycobacterium tuberculosis catalase-peroxidase (Mtb KatG) is a bifunctional enzyme that possesses both catalase and peroxidase activities and is responsible for the activation of the antituberculosis drug isoniazid. Mtb KatG contains an unusual adduct in its distal heme-pocket that consists of the covalently linked Trp107, Tyr229, and Met255. The KatG(Y229F) mutant lacks this adduct and has decreased steady-state catalase activity and enhanced peroxidase activity. In order to test a potential structural role of the adduct that supports catalase activity, we have used resonance Raman spectroscopy to probe the local heme environment of KatG(Y229F). In comparison to wild-type KatG, resting KatG(Y229F) contains a significant amount of 6-coordinate, low-spin heme and a more planar heme. Resonance Raman spectroscopy of the ferrous-CO complex of KatG(Y229F) suggest a non-linear Fe-CO binding geometry that is less tilted than in wild-type KatG. These data provide evidence that the Met-Tyr-Trp adduct imparts structural stability to the active site of KatG that seems to be important for sustaining catalase activity.

The diverse antioxidant systems of Helicobacter pylori

The gastric pathogen Helicobacter pylori induces a strong inflammatory host response, yet the bacterium maintains long-term persistence in the host. H. pylori combats oxidative stress via a battery of diverse activities, some of which are unique or newly described. In addition to using the well-studied bacterial oxidative stress resistance enzymes superoxide dismutase and catalase, H. pylori depends on a family of peroxiredoxins (alkylhydroperoxide reductase, bacterioferritin co-migratory protein and a thiol-peroxidase) that function to detoxify organic peroxides. Newly described antioxidant proteins include a soluble NADPH quinone reductase (MdaB) and an iron sequestering protein (NapA) that has dual roles - host inflammation stimulation and minimizing reactive oxygen species production within H. pylori. An H. pylori arginase attenuates host inflammation, a thioredoxin required as a reductant for many oxidative stress enzymes is also a chaperon, and some novel properties of KatA and AhpC were discovered. To repair oxidative DNA damage, H. pylori uses an endonuclease (Nth), DNA recombination pathways and a newly described type of bacterial MutS2 that specifically recognizes 8-oxoguanine. A methionine sulphoxide reductase (Msr) plays a role in reducing the overall oxidized protein content of the cell, although it specifically targets oxidized Met residues. H. pylori possess few stress regulator proteins, but the key roles of a ferric uptake regulator (Fur) and a post-transcriptional regulator CsrA in antioxidant protein expression are described. The roles of all of these antioxidant systems have been addressed by a targeted mutant analysis approach and almost all are shown to be important in host colonization. The described antioxidant systems in H. pylori are expected to be relevant to many bacterial-associated diseases, as genes for most of the enzymes carrying out the newly described roles are present in a number of pathogenic bacteria.

Chance and design—Proton transfer in water, channels and bioenergetic proteins

Proton transfer and transport in water, gramicidin and some selected channels and bioenergetic proteins are reviewed. An attempt is made to draw some conclusions about how Nature designs long distance, proton transport functionality. The prevalence of water rather than amino acid hydrogen bonded chains is noted, and the possible benefits of waters as the major component are discussed qualitatively.