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Recycling of the high valence States of heme proteins by cysteine residues of THIMET-oligopeptidase.

Ferreira JC, Icimoto MY, Marcondes MF, Oliveira V, Nascimento OR, Nantes IL - PLoS ONE (2013)

Bottom Line: The TOP-promoted recycling of the high valence states of the peroxidases to the respective resting form was accompanied by a significant decrease in the thiol content of the peptidolytic enzyme.The oxidation of TOP thiol groups by peroxidases did not promote the inactivating oligomerization observed in the oxidation promoted by the enzyme aging.These findings are discussed towards a possible occurrence of these reactions in cells.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, SP, Brasil ; Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo Andre, SP, Brasil.

ABSTRACT
The peptidolytic enzyme THIMET-oligopeptidase (TOP) is able to act as a reducing agent in the peroxidase cycle of myoglobin (Mb) and horseradish peroxidase (HRP). The TOP-promoted recycling of the high valence states of the peroxidases to the respective resting form was accompanied by a significant decrease in the thiol content of the peptidolytic enzyme. EPR (electron paramagnetic resonance) analysis using DBNBS spin trapping revealed that TOP also prevented the formation of tryptophanyl radical in Mb challenged by H2O2. The oxidation of TOP thiol groups by peroxidases did not promote the inactivating oligomerization observed in the oxidation promoted by the enzyme aging. These findings are discussed towards a possible occurrence of these reactions in cells.

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Mechanism of TOP oxidation by hydrogen peroxide.
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pone-0079102-g007: Mechanism of TOP oxidation by hydrogen peroxide.

Mentions: At this point it is important to consider the mechanisms involved in the oxidation of TOP by H2O2 and by the high valence states of hemeproteins. The mechanism of TOP thiol oxidation by H2O2 is probably the same as previously described for other proteins like bovine serum albumin [49,50]. In the uncatalysed oxidation, the mechanism probably occurs via a second order nucleophile displacement on oxygen. This mechanism may lead to thiol oxidation to sulfenic (–SOH, Figure 7), sulfinic (–SO2H) and sulfonic (–SO3H) acids and even to a combination of these thiol oxidized forms. Intramolecular disulfide has not been detected in partially oxidized TOP [12] and the formation of disulfide bonds is not expected when this enzyme is oxidized by H2O2.. However, the formation of disulfide by the spontaneous conversion of sulphenic acids to disulphides could not be discarded, and it remains to be determined (Figure 7). Considering that significant changes in the aggregated forms of TOP were not observed after treatment with hydrogen peroxide, one could conclude that the formation of intermolecular disulfide dimers were not favored. This result reinforces the idea TOP thiol groups are probably being oxidized beyond the disulfide. In cells, TOP-SOH could react with GSH to form TOP-SSG, which in turn could react with another cysteine residue to form disulfide bonds and GSH [12].Regarding the catalyzed mechanism, the proposal is depicted in Figures 8 (absence of TOP), 9 (presence of TOP) and 10 (fate of TOP thyil radical).


Recycling of the high valence States of heme proteins by cysteine residues of THIMET-oligopeptidase.

Ferreira JC, Icimoto MY, Marcondes MF, Oliveira V, Nascimento OR, Nantes IL - PLoS ONE (2013)

Mechanism of TOP oxidation by hydrogen peroxide.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3815109&req=5

pone-0079102-g007: Mechanism of TOP oxidation by hydrogen peroxide.
Mentions: At this point it is important to consider the mechanisms involved in the oxidation of TOP by H2O2 and by the high valence states of hemeproteins. The mechanism of TOP thiol oxidation by H2O2 is probably the same as previously described for other proteins like bovine serum albumin [49,50]. In the uncatalysed oxidation, the mechanism probably occurs via a second order nucleophile displacement on oxygen. This mechanism may lead to thiol oxidation to sulfenic (–SOH, Figure 7), sulfinic (–SO2H) and sulfonic (–SO3H) acids and even to a combination of these thiol oxidized forms. Intramolecular disulfide has not been detected in partially oxidized TOP [12] and the formation of disulfide bonds is not expected when this enzyme is oxidized by H2O2.. However, the formation of disulfide by the spontaneous conversion of sulphenic acids to disulphides could not be discarded, and it remains to be determined (Figure 7). Considering that significant changes in the aggregated forms of TOP were not observed after treatment with hydrogen peroxide, one could conclude that the formation of intermolecular disulfide dimers were not favored. This result reinforces the idea TOP thiol groups are probably being oxidized beyond the disulfide. In cells, TOP-SOH could react with GSH to form TOP-SSG, which in turn could react with another cysteine residue to form disulfide bonds and GSH [12].Regarding the catalyzed mechanism, the proposal is depicted in Figures 8 (absence of TOP), 9 (presence of TOP) and 10 (fate of TOP thyil radical).

Bottom Line: The TOP-promoted recycling of the high valence states of the peroxidases to the respective resting form was accompanied by a significant decrease in the thiol content of the peptidolytic enzyme.The oxidation of TOP thiol groups by peroxidases did not promote the inactivating oligomerization observed in the oxidation promoted by the enzyme aging.These findings are discussed towards a possible occurrence of these reactions in cells.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, SP, Brasil ; Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo Andre, SP, Brasil.

ABSTRACT
The peptidolytic enzyme THIMET-oligopeptidase (TOP) is able to act as a reducing agent in the peroxidase cycle of myoglobin (Mb) and horseradish peroxidase (HRP). The TOP-promoted recycling of the high valence states of the peroxidases to the respective resting form was accompanied by a significant decrease in the thiol content of the peptidolytic enzyme. EPR (electron paramagnetic resonance) analysis using DBNBS spin trapping revealed that TOP also prevented the formation of tryptophanyl radical in Mb challenged by H2O2. The oxidation of TOP thiol groups by peroxidases did not promote the inactivating oligomerization observed in the oxidation promoted by the enzyme aging. These findings are discussed towards a possible occurrence of these reactions in cells.

Show MeSH