Hydrogen-peroxide Oxidoreductase Research Articles

Safety evaluation of an extension of use of the food enzyme peroxidase from the genetically modified Aspergillus niger strain MOX.

The food enzyme peroxidase (phenolic donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) is produced with the genetically modified Aspergillus niger strain MOX by DSM Food Specialties B.V. A safety evaluation of this food enzyme was made previously, in which EFSA concluded that this food enzyme did not give rise to safety concerns when used in one food manufacturing process. Subsequently, the applicant requested to extend its use to include an additional process. In this assessment, EFSA updated the safety evaluation of this food enzyme when used in a total of two food manufacturing processes: processing of dairy products for the production of modified milk proteins and the production of plant-based analogues of milk and milk products. The dietary exposure to the food enzyme-total organic solids (TOS) was estimated to be up to 0.091 mg TOS/kg body weight (bw) per day in European populations. Using the no observed adverse effect level previously reported (2162 mg TOS/kg bw per day), the Panel derived a margin of exposure (MoE) of at least 23,758. Based on the data provided for the previous evaluation and the revised MoE, the Panel concluded that this food enzyme does not give rise to safety concerns under the revised intended conditions of use.

Safety evaluation of the food enzyme catalase from the non-genetically modified Aspergillus tubingensis strain AE-CN.

The food enzyme catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase; EC 1.11.1.6) is produced with the non-genetically modified Aspergillus tubingensis strain AE-CN by Amano Enzyme Inc. The absence of viable cells of the production organism in the food enzyme was not demonstrated. The food enzyme is intended to be used in five food manufacturing processes: production of baked products, processing of egg and egg products, production of fruit and vegetable products other than juices, production of cheese and production of fish roes. The dietary exposure to the food enzyme total organic solids (TOS) was estimated to be up to 0.325 mg TOS/kg body weight (bw) per day in European populations. The results of the in vitro genotoxicity studies indicated the presence of a clastogenic agent in the food enzyme which could not be dismissed due to limitations in the in vivo studies. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 323 mg TOS/kg bw per day, the highest dose tested. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and one match was found. The Panel considered that the risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood is low. Because of the results of the genotoxicity studies, and as the absence of viable cells from the production strain was not demonstrated, the Panel was unable to establish the safety of the food enzyme.

Safety evaluation of the food enzyme catalase from the non-genetically modified Aspergillus niger strain CTS 2093.

The food enzyme catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase; EC 1.11.1.6) is produced with the non-genetically modified Aspergillus niger strain CTS 2093 by Shin Nihon Chemical Co., Ltd. It is considered free from viable cells of the production organism. The food enzyme is intended to be used in eight food manufacturing processes: baking processes, cereal-based processes, coffee processing, egg processing, vegetable processing for juice production, processing of tea, herbal and fruit infusions, herring roe processing and milk processing for cheese production. Dietary exposure to the food enzyme-total organic solids (TOS) was estimated to be up to 3.61mg TOS/kg body weight (bw) per day in European populations. In addition, it is used in the production of acacia gum with the highest dietary exposure at the 95th percentile of 0.018mg TOS/kg bw per day in infants, when acacia gum is used as a food additive. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 56mg TOS/kg bw per day, the mid-dose tested, which, when compared with the estimated dietary exposure, resulted in a margin of exposure of 16. A search for similarity of the amino acid sequence of the food enzyme to known allergens was made and one match with a respiratory allergen was found. The Panel considered that, under the intended conditions of use, the risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood for this to occur is low. Based on the data provided, the Panel considered the margin of exposure as insufficient to exclude safety concerns under the intended conditions of use.

Safety evaluation of the food enzyme catalase from porcine liver.

The food enzyme catalase (hydrogen‐peroxide:hydrogen‐peroxide oxidoreductase; EC 1.11.1.6) is obtained from porcine liver by Avances Bioquímicos Alimentación, S.L. (Spain). The food enzyme is intended to be used in cheese production for decomposition of hydrogen peroxide in brine. The manufacturing process involves the use of a solvent not permitted in the production of foods and food ingredients according to Directive 2009/32/EC. Consequently, the food enzyme does not comply with the existing requirements in the EU.

Safety evaluation of the food enzyme catalase from the genetically modified Aspergillus niger strain DP-Azw58.

The food enzyme catalase (hydrogen‐peroxide:hydrogen‐peroxide oxidoreductase; EC 1.11.1.6) is produced with the genetically modified Aspergillus niger strain DP‐Azw58 by Danisco US, Inc. The genetic modifications do not give rise to safety concerns. The food enzyme is considered free from viable cells of the production organism and its DNA. It is intended to be used in egg processing. Based on the maximum use levels, dietary exposure to the food enzyme–total organic solids (TOS) was estimated to be up to 1 μg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90‐day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 1,288 mg TOS/kg bw per day, the highest dose tested, which when compared with the estimated dietary exposure, results in a margin of exposure of at least 1.3 × 106. A search for similarity of the amino acid sequence of the food enzyme to known allergens was made and one match was found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded, but the likelihood for this to occur is considered to be low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Radical addition polymerization: Enzymatic template-free synthesis of conjugated polymers and their nanostructure fabrication.

Conjugated polymers are attractive for many applications due to their unique properties. Their molecular structure can easily be tuned, making them suitable for an enormous number of specific applications. Conjugated polymers have the potential to achieve electrical properties similar to those of noncrystalline inorganic semiconductors; however, their chemical structure is much more complex and somewhat resembles that of biomacromolecules. The molecular conformation and interactions of conjugated polymers play an important role in their functionality. The use of enzymes has emerged as a highly valuable alternative method to synthesize these polymers and is very useful in the fabrication of their nanostructures. Here, we present established strategies for the synthesis of conjugated polymers in template-free systems that do not interfere with the preparation of their nanostructures. These strategies are based on the use of peroxidases (class III; EC 1.11.1.7, donor: hydrogen peroxide oxidoreductase), which are enzymes that have the ability to catalyze the oxidation of a number of compounds (including aromatics such as aniline, pyrrole, thiophene and some of their derivatives), in the presence of hydrogen peroxide, to obtain conjugated polymers.

Safety evaluation of the food enzyme peroxidase obtained from soybean (Glycine max) hulls.

The food enzyme considered in this opinion is a peroxidase (hydrogen‐peroxide oxidoreductase; EC 1.11.1.7) obtained from hulls of soybeans (Glycine max) by the company Kerry Ingredients & Flavours. The compositional data provided were considered sufficient. The manufacturing process did not raise safety concerns. The enzyme is intended to be used in baking processes. Based on the maximum recommended use level, dietary exposure to the food enzyme total organic solids (TOS) was estimated on the basis of individual data from the EFSA Comprehensive European Food Consumption Database. This exposure estimate is lower than the exposure to the fraction of soybean comparable to the food enzyme TOS resulting from the consumption of whole soybean‐derived foods by roughly an order of magnitude. As the food enzyme is derived from edible parts of soybean, in line with the requirements of the guidance document on food enzyme assessment, the Panel concluded that the provision of toxicological data was unnecessary. The potential allergenicity was evaluated by searching for similarity between the amino acid sequence of soybean peroxidase retrieved from the database Uniprot and the sequences of known food allergens; no match was found. Peroxidase from soybean hulls is not listed as an allergen in allergen databases. However, several soybean‐ and soybean hull proteins are known to be respiratory or food allergens. Based on the origin of the food enzyme from edible parts of soybean, the enzyme manufacturing process, the compositional and biochemical data provided, and the dietary exposure assessment, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use. However, the Panel noted that this food enzyme may contain allergenic soybean proteins, thus, adverse reactions in susceptible soybean‐allergic individuals cannot be ruled out.

Effect of Temperature on Guaiacol Peroxidase of <i>Pyrus communis</i>

Peroxidase (EC 1.11.1.7; donor: hydrogen-peroxide oxidoreductase, POD) is one of the key enzymes controlling plant growth, differentiation and development. The enzyme participates in construction, rigidification and eventual lignification of cell walls, biosynthesis of ethylene from 1-aminocyclopropane-1-carboxylic acid and H2O2, regulation of auxin level through auxin catabolism, protection of tissue from damage and infection by pathogenic microorganisms, the oxidation of indoleacetic acid. For peroxidase activity in wild pears extract one pH optimum was observed at 6.5 that probably belong to atleast one isoenzyme. Activity of peroxidase in presence of guaiacol and H2O2 was optimum after incubation at 40 °C. Maximum activity of peroxidase is 300% .Activity increased to 240%, 300%, 70% and 10% after 60 minute incubation at 30, 40, 45 and 60 °C for peroxidase. Incubation at high temperature (70 °C) was accompanied with decrease of activity to 10% peroxidase activity.

Effect of Temperature on Guaiacol Peroxidase of <i>Pyrus communis</i>

Peroxidase (EC 1.11.1.7; donor: hydrogen-peroxide oxidoreductase, POD) is one of the key enzymes controlling plant growth, differentiation and development. The enzyme participates in construction, rigidification and eventual lignification of cell walls, biosynthesis of ethylene from 1-aminocyclopropane-1-carboxylic acid and H2O2, regulation of auxin level through auxin catabolism, protection of tissue from damage and infection by pathogenic microorganisms, the oxidation of indoleacetic acid. For peroxidase activity in wild pears extract one pH optimum was observed at 6.5 that probably belong to atleast one isoenzyme. Activity of peroxidase in presence of guaiacol and H2O2 was optimum after incubation at 40 °C. Maximum activity of peroxidase is 300% .Activity increased to 240%, 300%, 70% and 10% after 60 minute incubation at 30, 40, 45 and 60 °C for peroxidase. Incubation at high temperature (70 °C) was accompanied with decrease of activity to 10% peroxidase activity.

Purification and Characterization of Peroxidase from Sweet Gourd (Cucurbita moschata Lam. Poiret)

Peroxidase (EC 1.11.1.7; donor: hydrogen peroxide oxidoreductase) is an oxidoreductase enzyme found in many fruits and vegetables. This enzyme was purified from sweet gourd (Cucurbita moschata Lam. Poiret) by ammonium sulphate precipitation and CM-Sephadex ion-exchange chromatography. Furthermore, optimum pH, optimum temperature, optimum ionic strength, stable pH, and stable temperature conditions were determined as 7.2, 50°C, 0.4 M, 8.0, and 40°C, respectively. The molecular weight (MW) of the enzyme was estimated to be 85 kDa by SDS-PAGE method. The values of Km and Vmax were calculated from the Lineweaver-Burk graph for guaiacol/H2O2 substrate patterns.

Purification and characterization of peroxidase from Turkish black radish (Raphanus sativus L.)

Peroxidases (EC 1.11.1.7; donor: hydrogen peroxide oxidoreductase) are part of a large group of enzymes associated with cell wall biosynthesis, response to injury, disease, resistance and wound repair. They catalyze the oxidation of various electron donor substrates such as phenols and aromatic amines in the presence of hydrogen peroxide. In the present study, peroxidase, a primer antioxidant enzyme, was purified 9.7 fold from Turkish black radish (Raphanus sativus L.) in a yield of 2% by ammonium sulphate precipitation, dialysis and CM-Sephadex ion exchange chromatography. To check the enzyme purity, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed and a single band was observed. The substrate specificity of peroxidase was investigated using guaiacol (2-methoxyphenol). Optimum pH, optimum temperature, optimum ionic strength, stable pH, stable temperature and thermal inactivation conditions were determined for guaiacol / H2O2 substrate pattern. These kinetic properties were found to be 6.0, 30°C, 1.0 M, 9.0, and 60°C, respectively. The molecular weight (Mw) of the enzyme was found to be 66 kDa by sodium dodecyl sulphatepolyacrylamide gel electrophoresis (SDS - PAGE) method. Native polyacrylamide gel electrophoresis (Native-PAGE) was performed for isoenzyme determination and a single band was observed. Km and Vmax values were calculated from Lineweaver-Burk graphs.

Evaluation of the effect of ammonium carbamate on the stability of proteins

AbstractBACKGROUND: The use of the volatile salt ammonium carbamate in protein downstream processing has recently been proposed. The main advantage of using volatile salts is that they can be removed from precipitates and liquid effluents through pressure reduction or temperature increase. Although previous studies showed that ammonium carbamate is efficient as a precipitant agent, there was evidence of denaturation in some enzymes. In this work, the effect of ammonium carbamate on the stability of five enzymes was evaluated.RESULTS: Activity assays showed that α‐amylase (1,4‐α–D‐glucan glucanohydrolase, EC 3.2.1.1), lysozyme (1,4‐β‐N‐acetylmuramoylhydrolase, EC 3.2.1.17) and lipase (triacyl glycerol acyl hydrolase, EC 3.1.1.3) did not undergo activity loss in ammonium carbamate solutions with concentrations from 1.0 to 5.0 mol kg−1, whereas cellulase complex (1,4‐(1,3:14)‐β‐D‐glucan 4‐glucano‐hydrolase, EC 3.2.1.4) and peroxidase (hydrogen peroxide oxidoreductase, EC 1.11.1.7) showed an average activity loss of 55% and 44%, respectively. Precipitation assays did not show enzyme denaturation or phase separation for α‐amylase and lipase, while celullase and peroxidase precipitated with some activity reduction. Analysis of similar experiments with ammonium and sodium sulfate did not affect the activity of enzymes.CONCLUSION: Celullase and peroxidase were denatured by ammonium carbamate. While more systematic studies are not available, care must be taken in designing a protein precipitation with this salt. The results suggest that the generally accepted idea that salts that denature proteins tend to solubilize them does not hold for ammonium carbamate. Copyright © 2010 Society of Chemical Industry

Purification and Characterization of Peroxidase from Cauliflower (Brassica oleracea L. var. botrytis) Buds

Peroxidases (EC 1.11.1.7; donor: hydrogen peroxide oxidoreductase) are part of a large group of enzymes. In this study, peroxidase, a primer antioxidant enzyme, was purified with 19.3 fold and 0.2% efficiency from cauliflower (Brassica oleracea L.) by ammonium sulphate precipitation, dialysis, CM-Sephadex ion-exchange chromatography and Sephadex G-25 purification steps. The substrate specificity of peroxidase was investigated using 2,2'-azino-bis(3-ethylbenz-thiazoline-6-sulphonic acid) (ABTS), 2-methoxyphenol (guaiacol), 1,2-dihydroxybenzene (catechol), 1,2,3-trihyidroxybenzene (pyrogallol) and 4-methylcatechol. Also, optimum pH, optimum temperature, optimum ionic strength, stable pH, stable temperature, thermal inactivation conditions were determined for guaiacol/H(2)O(2), pyrogallol/H(2)O(2), ABTS/H(2)O(2), catechol/H(2)O(2) and 4-methyl catechol/H(2)O(2) substrate patterns. The molecular weight (M(w)) of this enzyme was found to be 44 kDa by gel filtration chromatography method. Native polyacrylamide gel electrophoresis (PAGE) was performed for isoenzyme determination and a single band was observed. K(m) and V(max) values were calculated from Lineweaver-Burk graph for each substrate patterns.

Antioxidant potential of fluoxetine in comparison to Curcuma longa in restraint-stressed rats

Stress plays a potential role in the onset and exacerbation of depression. Chronic restraint stress in rats, and psychosocial stress in humans, is implicated in the pathophysiology of mood and anxiety disorders. Oxidative damage is an established outcome of restraint stress, which has been suggested to induce many damaging processes contributing to the pathology of stress-induced depression. However, the modulatory role of clinically effective antidepressants, such as fluoxetine, in attenuating oxidative stress has not been well characterized. Therefore, the current study was designed to investigate the antioxidant effects of chronic treatment with fluoxetine in animals submitted to restraint stress. The antioxidant potential of the antidepressant fluoxetine was compared with that of turmeric, used as a standard since it integrates both antioxidant and antidepressant properties. Chronic fluoxetine administration to stressed animals for 21 days prevented restraint stress-induced oxidative damage with an efficacy similar to that of turmeric, as evidenced by significant enhancement of key endogenous antioxidant defense components, comprising the free-radical scavenging enzymes, superoxide:superoxide oxidoreductase (EC 1.15.1.1), hydrogen-peroxide:hydrogen-peroxide oxidoreductase (EC 1.11.1.6), glutathione S-transferase (EC 2.5.1.18) and glutathione:NADP(+)oxidoreductase (EC 1.8.1.7), as well as non-enzymatic antioxidants, GSH, glucose and uric acid, which were severely depleted by restraint stress in animals receiving no treatment. Oxidative stress markers, (S)-lactate:NAD(+) oxidoreductase activity (EC 1.1.1.27), malondialdehyde levels (lipid peroxidation product) and protein carbonyl content were also significantly decreased following fluoxetine treatment. Both these drugs when given alone to non-stressed animals did not alter basal levels of antioxidant defense components and oxidative stress markers significantly. Our findings suggest that the therapeutic efficacy of fluoxetine may be mediated, at least partially, via reversal of oxidative damage as demonstrated by protective enhancement of antioxidant status following a stress-induced decline. In addition, this study demonstrates important implications for pharmacological interventions targeting cellular antioxidants as a promising strategy for protecting against oxidative insults in stress-induced depression.

Partial characterization of peroxidase from the leaves of thymbra plant (Thymbra spicata L. var. spicata)

Peroxidase (EC 1.11.1.7; donor: hydrogen-peroxide oxidoreductase) catalyses the oxidation of various electron donor substrates (e.g. phenols, aromatic amines). In this study, the peroxidase was extracted from Thymbra spicata L. var. spicata and, then partially purified with (NH4)2SO4 precipitation and dialysis. The substrate specificity of peroxidase was investigated using 2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS), o-dianisidine, o-phenylenediamine, catechol and guaiacol as substrates. Furthermore, the effects of buffer concentration, pH, temperature and thermal inactivation on enzyme activity were also studied. The results obtained have shown that (i) the best substrate is o-dianisidine, followed by ABTS, catechol, guaiacol and o-phenylenediamine, respectively; (ii) the best buffer concentration is 40 mM for o-dianisidine and catechol, 10 mM for ABTS and guaiacol, and 100 mM for o-phenylenediamine; (iii) optimum pH is 2.5 for ABTS and o-phenylenediamine, 6.0 for o-dianisidine, and 7.0 for catechol and guaiacol; (iv) optimum temperature is 20 °C for catechol, 40 °C for ABTS, guaiacol and o-dianisidine, and 50 °C for o-phenylenediamine; and (v) the enzyme activity in the thermal inactivation experiments was enhanced with increase in temperature with o-dianisidine as a substrate while its activity decreased with o-phenylenediamine.

Redox Thermodynamics of the Fe(III)/Fe(II) Couple of Human Myeloperoxidase in Its High-Spin and Low-Spin Forms

Myeloperoxidase (MPO) (donor, hydrogen peroxide oxidoreductase, EC 1.11.1.7) is the most abundant neutrophil enzyme and catalyzes predominantly the two-electron oxidation of ubiquitous chloride (Cl-), to generate the potent bleaching oxidant hypochlorous acid (HOCl), thus contributing to bacterial killing and inflammatory reactions of neutrophils. Here, the thermodynamics of the one-electron reduction of the ferric heme in its ferric high-spin and cyanide-bound low-spin forms were determined through spectroelectrochemical experiments. The E(o)' values for free and cyanide-bound MPO (5 and -37 mV, respectively, at 25 degrees C and pH 7.0) are significantly higher than those of other heme peroxidases. Variable-temperature experiments revealed that the enthalpic stabilization of ferric high-spin MPO is much weaker than in other heme peroxidases and is exactly compensated by the entropic change upon reduction. In contrast to those of other heme peroxidases, the stabilization of the ferric cyanide-bound MPO is also very weak and fully entropic. This peculiar behavior is discussed with respect to the MPO-typical covalent heme to protein linkages as well as to the published structures of ferric MPO and its cyanide complex and the recently published structure of lactoperoxidase as well as the physiological role of MPO in bacterial killing.

Catalase Activity Assays

Catalase (hydrogen peroxide/hydrogen peroxide oxidoreductase) is an important cellular antioxidant enzyme that defends against oxidative stress. It is found in the peroxisomes of most aerobic cells. It serves to protect the cell from toxic effects of high concentrations of hydrogen peroxide (H(2)O(2)) by catalyzing its decomposition into molecular oxygen and water, without the production of free radicals. It is important to measure catalase levels because oxidative stress is inherent in pathological conditions such as cancer, diabetes, cataracts, atherosclerosis, neurodegenerative disease, aging, and nutritional deficiencies. This unit provides methods for catalase activity measurements.

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

BackgroundA potentially lethal flux of hydrogen peroxide (H2O2) is continuously generated during aerobic metabolism. It follows that aerobic organisms have equipped themselves with specific H2O2 dismutases and H2O2 reductases, of which catalase and the alkyl hydroperoxide reductase (AhpR) are the best-studied prokaryotic members. The sequenced Haemophilus influenzae Rd genome reveals one catalase, designated HktE, and no AhpR. However, Haemophilus influenzae type b strain Eagan (Hib), a causative agent of bacterial sepsis and meningitis in young children, disrupted in its hktE gene is not attenuated in virulence, and retains the ability to rapidly scavenge H2O2. This redundancy in H2O2-scavenging is accounted for by peroxidatic activity which specifically uses glutathione as the reducing substrate.ResultsWe show here that inside acatalasaemic H. influenzae all of the residual peroxidatic activity is catalyzed by PGdx, a hybrid peroxiredoxin-glutaredoxin glutathione-dependent peroxidase. In vitro kinetic assays on crude hktE- pgdx- H. influenzae Rd extracts revealed the presence of NAD(P)H:peroxide oxidoreductase activity, which, however, appears to be physiologically insignificant because of its low affinity for H2O2 (Km = 1.1 mM). Hydroperoxidase-deficient hktE- pgdx- H. influenzae Rd showed a slightly affected aerobic growth phenotype in rich broth, while, in chemically defined medium, growth was completely inhibited by aerobic conditions, unless the medium contained an amino acid/vitamin supplement. To study the role of PGdx in virulence and to assess the requirement of H2O2-scavenging during the course of infection, both a pgdx single mutant and a pgdx/hktE double mutant of Hib were assayed for virulence in an infant rat model. The ability of both mutant strains to cause bacteremia was unaffected.ConclusionCatalase (HktE) and a sole peroxidase (PGdx) account for the majority of scavenging of metabolically generated H2O2 in the H. influenzae cytoplasm. Growth experiments with hydroperoxidase-deficient hktE- pgdx- H. influenzae Rd suggest that the cytotoxicity inflicted by the continuous accumulation of H2O2 during aerobic growth brings about bacteriostasis rather than bacterial killing. Finally, H2O2-scavenging is not a determinant of Hib virulence in the infant rat model of infection.

Purification of two peroxidase isoenzymes of Aloe barbadensis which oxidize p-coumaric acid

Using a combination of hydrophobicity and ion-exchange chromatography methods, one cationic (p I 9.0) and one anionic (p I 4.5) peroxidase (donor: hydrogen-peroxide oxidoreductase; EC 1.11.1.7) isoenzymes of Aloe barbadensis have been purified (the cationic peroxidase to homogeneity as judged by SDS-PAGE analysis and microsequencing). This allowed us to initiate the investigation of individual catalytic properties to be related to their respective functions in vivo. The two peroxidases have an optimal activity at pH 6.0. Apparent affinities for H 2O 2 range between 0.01 and 0.14 mM depending on the phenolic substrate and the isoenzyme. The apparent K m values for the phenolics ( p-coumaric acid and hydroquinone) are some 25-fold lower in the anionic (around 0.02 mM) than in the cationic (around 0.77 and 0.34 mM, respectively) isoenzyme. The possible functions of the activities are discussed.

Oxidation of phenolic compounds from Aloe barbadensis by peroxidase activity: Possible involvement in defence reactions

Sephadex LH-20 chromatography and reverse phase-high performance liquid chromatography (RP-HPLC) have been combined to analyse different phenolics in Aloe barbadensis Mill. Among them, a new chromone peak was found. Whole phenolics, and anthrone and chromone fractions were assayed as substrates of endogenous peroxidases (donor:hydrogen-peroxide oxidoreductase; EC 1.11.1.7) and polyphenol oxidases (1,2-benzenediol:oxygen oxidoreductase; EC 1.10.3.1) by following the disappearance of specific RP-HPLC peaks after appropriate incubations in the presence and in absence of H 2O 2. Chromones, but not anthrones, were found to be good substrates of peroxidases. It is postulated that peroxidase oxidation of chromones may have a protective and sealing effect against infection after wounding. Polyphenol oxidases may have a secondary, if any, effect.