TY - JOUR
T1 - Photo-oxidation-induced inactivation of the selenium-containing protective enzymes thioredoxin reductase and glutathione peroxidase
AU - Suryo Rahmanto, Aldwin
AU - Pattison, David I
AU - Davies, Michael Jonathan
N1 - Copyright © 2012 Elsevier Inc. All rights reserved.
PY - 2012/9/15
Y1 - 2012/9/15
N2 - Singlet oxygen (1O2) is a reactive oxygen species generated during photo-oxidation, inflammation, and via peroxidase-catalyzed reactions (e.g., myeloperoxidase and eosinophil peroxidase). 1O 2 oxidizes the free amino acids Trp, Tyr, His, Cys, and Met, and those species present on peptides/proteins, with this resulting in modulation of protein structure and function. Impairment of the activity of antioxidant enzymes may be of relevance to the oxidative stress observed in a number of pathologies involving either light exposure or inflammation. In this study, the effects of 1O2 on glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) activity, including the mechanisms of their inactivation, were investigated. Exposure of GPx or TrxR, either as purified proteins or in cell lysates, to Rose Bengal and visible light (an established source of 1O2) resulted in significant, photolysis time-dependent reductions in enzyme activity (10-40%, P<0.05). More extensive inhibition (ca. 2-fold) was detected when the reactions were carried out in D2O, consistent with the intermediacy of 1O2. No additional inhibition was detected after the cessation of photolysis, eliminating a role for photo-products. Methionine, which reacts rapidly with 1O2 (k∼107 M-1 s -1), significantly reduced photo-inactivation at large molar excesses, presumably by acting as an alternative target. Reductants (NaBH4, DTT, GSH, or NADPH) added after the cessation of 1O2 formation were unable to reverse enzyme inactivation, consistent with irreversible enzyme oxidation. Formation of nonreducible protein aggregates and/or fragments was detected for both photo-oxidized GPx and TrxR by SDS-PAGE. An oxidant concentration-dependent increase in protein carbonyls was detected with TrxR but not GPx. These studies thus demonstrate that the antioxidant enzymes GPx and TrxR can be irreversibly inactivated by 1O2.
AB - Singlet oxygen (1O2) is a reactive oxygen species generated during photo-oxidation, inflammation, and via peroxidase-catalyzed reactions (e.g., myeloperoxidase and eosinophil peroxidase). 1O 2 oxidizes the free amino acids Trp, Tyr, His, Cys, and Met, and those species present on peptides/proteins, with this resulting in modulation of protein structure and function. Impairment of the activity of antioxidant enzymes may be of relevance to the oxidative stress observed in a number of pathologies involving either light exposure or inflammation. In this study, the effects of 1O2 on glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) activity, including the mechanisms of their inactivation, were investigated. Exposure of GPx or TrxR, either as purified proteins or in cell lysates, to Rose Bengal and visible light (an established source of 1O2) resulted in significant, photolysis time-dependent reductions in enzyme activity (10-40%, P<0.05). More extensive inhibition (ca. 2-fold) was detected when the reactions were carried out in D2O, consistent with the intermediacy of 1O2. No additional inhibition was detected after the cessation of photolysis, eliminating a role for photo-products. Methionine, which reacts rapidly with 1O2 (k∼107 M-1 s -1), significantly reduced photo-inactivation at large molar excesses, presumably by acting as an alternative target. Reductants (NaBH4, DTT, GSH, or NADPH) added after the cessation of 1O2 formation were unable to reverse enzyme inactivation, consistent with irreversible enzyme oxidation. Formation of nonreducible protein aggregates and/or fragments was detected for both photo-oxidized GPx and TrxR by SDS-PAGE. An oxidant concentration-dependent increase in protein carbonyls was detected with TrxR but not GPx. These studies thus demonstrate that the antioxidant enzymes GPx and TrxR can be irreversibly inactivated by 1O2.
KW - Animals
KW - Borohydrides
KW - Cattle
KW - Cell Extracts
KW - Cell Line
KW - Dithiothreitol
KW - Enzyme Stability
KW - Free Radical Scavengers
KW - Glutathione
KW - Glutathione Peroxidase
KW - Hydrogen Peroxide
KW - Methionine
KW - Mice
KW - Oxidants, Photochemical
KW - Oxidation-Reduction
KW - Photolysis
KW - Protein Carbonylation
KW - Rats
KW - Reducing Agents
KW - Rose Bengal
KW - Singlet Oxygen
KW - Thioredoxin-Disulfide Reductase
U2 - 10.1016/j.freeradbiomed.2012.07.016
DO - 10.1016/j.freeradbiomed.2012.07.016
M3 - Journal article
C2 - 22884457
SN - 0891-5849
VL - 53
SP - 1308
EP - 1316
JO - Free Radical Biology & Medicine
JF - Free Radical Biology & Medicine
IS - 6
ER -