Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.11.1.7 (peroxidase)
 65,474 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rate constants for the reaction between horseradish peroxidase compound I and p-cresol have been determined at several values of pH between 2.98 and 10.81. These rate constants were used to construct a log (rate) versus pH profile from which it is readily seen that the most reactive form of the enzyme is its most basic form within this pH range so that base catalysis is occurring. At the maximum rate a second order rate constant of (5.1 +/- 0.3) x 10(-7) M-1 s-1 at 25 degrees is obtained. The activation energy of the reaction at the maximum rate was determined from an Arrhenius plot to be 5.0 +/- 0.5 kcal/mol. Evidence for an exception to the generally accepted enzymatic cycle of horseradish peroxidase is presented. One-half molar equivalent of p-cresol can convert compound I quantitatively to compound II at high pH, whereas usually this step requires 1 molar equivalent of reductant. The stoichiometry of this reaction is pH-dependent.
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PMID:Oxidation of p-cresol by horseradish peroxidase compound I. 0 11

Over a wide range of pH horseradish peroxidase compound I can be reduced quantitatively via compound II to the native enzyme by only 1 molar equivalent of p-cresol. Since 2 molar equivalents of electrons are required for the single turnover of the enzymatic cycle, p-cresol behaves as a 2-electron reductant. With p-cresol and compound I in a 1:1 ratio compound II and p-methylphenoxy radicals are obtained in the transient state. Compound II is then reduced to the native enzyme. A possible explanation for the facile reduction of compound II involves reaction with the dimerization product of these radicals, 1/2 molar equivalent of 2,2'-dihydroxy-5,5'-dimethylbiphenyl. If only 1/2 molar equivalent of p-cresol is present, than at high pH the reduction stops at compound II. The major steady state peroxidase oxidation product of p-cresol (with p-cresol in large excess compared to the enzyme concentration) is Pummerer's ketone. Pummerer's ketone is only reactive at pH values greater than about 9 where significant amounts of the enol can be formed via the enolate anion. Therefore, in alkaline solution it is reactive with compound I, but not with compound II, which is converted into an unreactive basic form. These results indicate that Pummerer's ketone cannot be the intermediate free radical product responsible for reducing compound II in the single turnover experiments. It is postulated that Pummerer's ketone is formed only in the steady state by the reaction of the p-methylphenoxy radical with excess p-cresol.
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PMID:Stoichiometry of the reaction between horseradish peroxidase and p-cresol. 0 12

Hematin can substitute for horseradish peroxidase (HRP) as the catalyst in the determination of hydrogen peroxide using phenolic substrates such as p-hydroxyphenylacetate or p-cresol. Although the peroxidatic activity of hematin from bovine blood is not as great as HRP in terms of unit iron content, the activity per unit weight is substantially greater. Hematin is 500 times less expensive than HRP per unit peroxidatic activity. In hematin-catalyzed systems, reaction development and fluorescence measurement can both be conducted optimally in the same ammoniacal buffer. Hydroxyalkyl hydroperoxides are rapidly hydrolyzed to H2O2 at this pH and are also determined. On the other hand, for methyl hydroperoxide, hematin exhibits only approximately 10% of the sensitivity exhibited by HRP. Hematin is significantly more stable in solution than HRP. The use of hematin as catalyst and p-cresol as the substrate leads to a particularly inexpensive and sensitive system, permitting a limit of detection (LOD) of 7 nM H2O2 in a flow-injection configuration.
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PMID:Hematin as a peroxidase substitute in hydrogen peroxide determinations. 157 21

Hydroquinone, a metabolite of benzene, is converted by human myeloperoxidase to 1,4-benzoquinone, a highly toxic species. This conversion is stimulated by phenol, another metabolite of benzene. Here we report that peroxidase-dependent hydroquinone metabolism is also stimulated by catechol, resorcinol, o-cresol, m-cresol, p-cresol, guaiacol, histidine, and imidazole. In order to gain insights into the mechanisms of this stimulation, we have compared the kinetics of human myeloperoxidase-dependent phenol, hydroquinone, and catechol metabolism. The specificity (Vmax/Km) of hydroquinone for myeloperoxidase was found to be 5-fold greater than that of catechol and 16-fold greater than that of phenol. These specificities for myeloperoxidase-dependent metabolism inversely correlated with the respective one-electron oxidation potentials of hydroquinone, catechol, and phenol and suggested that phenol- and catechol-induced stimulation of myeloperoxidase-dependent hydroquinone metabolism cannot simply be explained by interaction of hydroquinone with stimulant-derived radicals. Phenol (100 microM), catechol (20 microM), and imidazole (50 mM) did, however, all increase the specificity (Vmax/Km) of hydroquinone for myeloperoxidase, indicating that these three compounds may be stimulating hydroquinone metabolism by a common mechanism. Interestingly, the stimulation of peroxidase-dependent hydroquinone metabolism by other phenolic compounds was pH-dependent, with the stimulating effect being higher under alkaline conditions. These results therefore suggest that the interaction of phenolic compounds, presumably by hydrogen-bonding, with the activity limiting distal amino acid residue(s) or with the ferryl oxygen of peroxidase may be an important contributing factor in the enhanced myeloperoxidase-dependent metabolism of hydroquinone in the presence of other phenolic compounds.
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PMID:Metabolism of hydroquinone by human myeloperoxidase: mechanisms of stimulation by other phenolic compounds. 165 82

Guaiacol peroxidase from spinach catalyzes the oxidation of p-aminophenol to produce the aminophenoxy radical as the primary product which is converted further into a stable oxidation product with an absorption peak at 470 nm. The p-aminophenol radicals oxidize ascorbate (AsA) to produce monodehydroascorbate radicals. Kinetic analysis indicates that p-aminophenol radicals also oxidize monodehydroascorbate to dehydroascorbate. Incubation of AsA peroxidase from tea leaves and hydrogen peroxide with p-aminophenol, p-cresol, hydroxyurea, or hydroxylamine results in the inactivation of the enzyme. No inactivation of the enzyme was found upon incubation of the enzyme with these compounds either in the absence of hydrogen peroxide or with the stable oxidized products of these compounds. The enzyme was protected from inactivation by the inclusion of AsA in the incubation mixture. The radicals of p-aminophenol and hydroxyurea were produced by AsA peroxidase as detected by their ESR signals. These signals disappeared upon the addition of AsA, and the signal characteristic of monodehydroascorbate was found. Thus, AsA peroxidase is inactivated by the radicals of p-aminophenol, p-cresol, hydroxyurea, and hydroxylamine which are produced by the peroxidase reaction, and it is protected from inactivation by AsA via the scavenging of the radicals. Thus, these compounds are the suicide inhibitors for AsA peroxidase. Isozyme II of AsA peroxidase, which is localized in chloroplasts, is more sensitive to these compounds than isozyme I. In contrast to AsA peroxidase, guaiacol peroxidase was not affected by these various compounds, even though each was oxidized by it and the corresponding radicals were produced.
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PMID:Hydroxyurea and p-aminophenol are the suicide inhibitors of ascorbate peroxidase. 215 59

We investigated whether changes in plasma oxidative properties could occur after oral (hormonal) contraceptive (OC) administration in female rats and whether such changes could be responsible for the platelet increase in aggregation and lipid biosynthesis observed with that treatment. Platelets and plasma (platelet-poor) from control and OC (ethinyl estradiol + lynestrenol)-treated rats were prepared separately. Thrombin-induced aggregation of control platelets was markedly enhanced after incubation for 4 (p less than 0.025) to 60 (p less than 0.001) minutes in OC as compared with control plasma. Under the same conditions, platelet lipid biosynthesis was increased also (p less than 0.05 to p less than 0.01), but after 3 hours incubation. The enhanced response of platelets to aggregation induced by OC plasma could be inhibited by adding either glutathione (p less than 0.025), vitamin E (p less than 0.025), catalase (p less than 0.05), or peroxidase + glutathione (p less than 0.005) to plasma or 2,6,di-bis(ter-butyl)p-cresol (p less than 0.05) to platelets before incubation. The peroxidized free fatty acids isolated from OC plasma added to normal platelets induced a 150% (p less than 0.001) increase in the response to thrombin as compared with the fatty acids from control plasma. In addition, the level of malondialdehyde and conjugated dienes was significantly (p less than 0.02 to p less than 0.001) increased in OC compared with control plasma. We conclude that the enhanced formation in plasma of lipid hydroperoxides seems to be the initial event stimulating platelets after OC treatment, at least in rats.
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PMID:Hormonal contraceptive increases plasma lipid peroxides in female rats. Relationship to platelet aggregation and lipid biosynthesis. 253 71

The one- or two-electron oxidation of thyroglobulin by the thyroid peroxidase system was found to be regulated by the iodine content of thyroglobulin. The catalytic intermediate of thyroid peroxidase observed at steady state of the reaction was Compound I and II when the iodine content in thyroglobulin was 0.2 and 0.7%, respectively, apparent rate constants for the rate-limiting steps being estimated at 4.7 x 10(7) and 4.8 x 10(4) M-1 S-1. The thyroglobulin-mediated oxidation of GSH occurred by way of two-electron transfer at 0.2% iodine content and by way of one-electron transfer at 0.7% iodine content. The spin-trapping experiment with 5,5-dimethyl-1-pyrroline-N-oxide showed that glutathione radicals were formed in the latter reaction but not in the former. In the reactions of thyroid peroxidase, the one- and two-electron oxidations of ascorbate were also mediated by 0.2 and 0.7% iodine thyroglobulins, respectively. The reactions were analyzed and mimicked with the use of p-cresol and p-acetaminophenol as a mediator in the reactions of lactoperoxidase and thyroid peroxidase.
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PMID:Thyroglobulin-mediated one- and two-electron oxidations of glutathione and ascorbate in thyroid peroxidase systems. 254 39

On the basis of optical difference spectra, lactoperoxidase (LPO) was shown to form a 1:1 complex with aromatic donor molecules: resorcinol, hydroquinone, phenol, p-cresol, guaiacol, aniline, and benzohydroxamic acid. As compared with horseradish peroxidase (HRP), the values of the dissociation constant, Kd, of LPO-donor complexes were found to be 4-720-fold larger and were not greatly changed in the presence of KCN and by changes in pH in the range 4-9. The apparent enthalpy and entropy of the binding reactions were found to be -13 kJ mol-1 and -29 J mol-1 K-1, respectively, somewhat smaller (in absolute value) than the corresponding values of HRP. The difference spectra of LPO-donor complexes resembled each other, in contrast to the case of HRP, and the bindings of the donors to LPO occurred in a competitive fashion between the donors. Incubation of LPO with phenylhydrazine and hydrogen peroxide markedly depressed donor binding, the intensity of the Soret band, and the catalytic activity, probably as the result of formation of meso-phenyl derivatives of the heme. These findings suggest that the binding of aromatic donors to LPO occurs at a specific site, probably near the heme edge, where the electron transfer in the peroxidase reaction may take place.
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PMID:Interaction of aromatic donor molecules with lactoperoxidase probed by optical difference spectra. 273 Aug 81

The 15,000xg supernatant of sonicated rat PMN contains 5-lipoxygenase that converts arachidonic acid to 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and leukotriene A4 and an HPETE peroxidase that catalyzes reduction of the 5-HPETE. The specificity of this HPETE peroxidase for peroxides, reducing agents, and inhibitors has been characterized to distinguish this enzyme from other peroxidase activities. In addition to 5-HPETE, the HPETE peroxidase will catalyze reduction of 15-hydroperoxyeicosatetraenoic acid, 13-hydroperoxyoctadecadienoic acid, and 15-hydroperoxy-8,11,13-eicosatrienoic acid, but not cumene or t-butylhydroperoxides. The HPETE peroxidase accepted 5 of 11 thiols tested as reducing agents. However, glutathione is greater than 15 times more effective than any other thiol tested. Other reducing agents, ascorbate, NADH, NADPH, phenol, p-cresol, and homovanillic acid, were not accepted by HPETE peroxidase. This enzyme is not inhibited by 10 mM KCN, 2 mM aspirin, 2 mM salicylic acid, or 0.5 mM indomethacin. When 5-[14C]HPETE is generated from [14C]arachidonic acid in the presence of unlabeled 5-HPETE and the HPETE peroxidase, the 5-[14C]HETE produced is of much lower specific activity than the [14C]arachidonic acid. This indicates that the 5-[14C]HPETE leaves the active site of 5-lipoxygenase and mixes with the unlabeled 5-HPETE in solution prior to reduction and is a kinetic demonstration that 5-lipoxygenase has no peroxidase activity. Specificity for peroxides, reducing agents, and inhibitors differentiates HPETE peroxidase from glutathione peroxidase, phospholipid-hydroperoxide glutathione peroxidase, a 12-HPETE peroxidase, and heme peroxidases. The HPETE peroxidase could be a glutathione S-transferase selective for fatty acid hydroperoxides.
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PMID:Specificity of an HPETE peroxidase from rat PMN. 285 18

Peroxidase activity was partially purified from neonatal (3 to 6 days old) rat skin. The membrane-bound peroxidase activity was extracted with 0.5 M calcium chloride and was monitored spectrophotometrically at 470 nm with 2-methoxyphenol (guaiacol) and hydrogen peroxide as substrates. Subcellular distribution studies indicated the activity to be highest and comparable in nuclei and mitochondria, lowest in microsomes, and absent in cytosol. The peroxidase activity was partially purified by affinity chromatography on concanavalin A-sepharose 4B and by gel filtration using Bio-Gel P-150. Purification factors from these two steps were about 25 and 4, respectively. Peroxidase extraction in the presence of 2 mM N-ethylmaleimide increased activity about twofold. The combination of 2 mM N-ethylmaleimide and 10% (w/v) glycerol was found to be optimal for preservation of activity. Peroxidase activity increased linearly with increases in protein concentration, time, and guaiacol concentration. Activity was inhibited approximately 75% by 0.1 mM potassium cyanide or 0.05 mM sodium azide. Pyrogallol, hydroquinone, p-cresol, catechol, benzidine, 3,3'-dimethoxybenzidine, tetramethylbenzidine and p-phenylenediamine also acted as substrates for the rat cutaneous peroxidase.
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PMID:Peroxidase, an alternate pathway to cytochrome P-450 for xenobiotic metabolism in skin: partial purification and properties of the enzyme from neonatal rat skin. 285 75


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