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Mariaarmineh Tossounian - One of the best experts on this subject based on the ideXlab platform.
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disulfide bond formation protects arabidopsis thaliana glutathione transferase tau 23 from oxidative damage
Biochimica et Biophysica Acta, 2017Co-Authors: Mariaarmineh Tossounian, Khadija Wahni, Didier Vertommen, Inge Van Molle, Silke Jacques, Frank Van Breusegem, Kris Gevaert, David Young, Leonardo Astolfi Rosado, Joris MessensAbstract:Abstract Background Glutathione transferases play an important role as detoxifying enzymes. In A. thaliana, elevated levels of reactive oxygen species (ROS), provoked during biotic and abiotic stress, influence the activity of GSTU23. The aim of this study is to determine the impact of oxidative stress on the function and structure of GSTU23. Methods The impact of oxidation on the function of GSTU23 was studied using a glutathione transferase biochemical assay and mass spectrometry. With kinetics, circular dichroism and thermodynamics, we compared reduced with oxidized GSTU23. X-ray crystal structures of GSTU23 visualize the impact of oxidation on methionines and cysteines. Results In the presence of 100 μM H2O2, oxidation of the methionine side-chain to a sulfoxide is the prominent post-translational modification, which can be reduced by C. diphtheriae MsrA and MsrB. However, increasing the level to 200 μM H2O2 results in a reversible intramolecular disulfide between Cys65-Cys110, which is substrate for glutaredoxin. Under these oxidizing conditions, GSTU23 undergoes a structural change and forms a more favourable enzyme-substrate complex to overcome kcat decrease. Conclusions and significance At lower H2O2 levels (100 μM), GSTU23 forms methionine sulfoxides. Specifically, oxidation of Met14, located near the catalytic Ser13, could interfere with both GSH binding and catalytic activation. At higher H2O2 levels (200 μM), the Cys65-Cys110 disulfide bond protects other cysteines and also methionines from overoxidation. This study shows the impact of oxidative stress on GSTU23 regulated by methionine sulfoxide reductases and glutaredoxin, and the mechanisms involved in maintaining its catalytic functionality under oxidizing conditions.
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corynebacterium diphtheriae methionine sulfoxide reductase a exploits a unique mycothiol redox relay mechanism
Journal of Biological Chemistry, 2015Co-Authors: Mariaarmineh Tossounian, Brandan Pedre, Khadija Wahni, Huriye Erdogan, Didier Vertommen, Inge Van MolleAbstract:Methionine sulfoxide reductases are conserved enzymes that reduce oxidized methionines in proteins and play a pivotal role in cellular redox signaling. We have unraveled the redox relay mechanisms of methionine sulfoxide reductase A of the pathogen Corynebacterium diphtheriae (Cd-MsrA) and shown that this enzyme is coupled to two independent redox relay pathways. Steady-state kinetics combined with mass spectrometry of Cd-MsrA mutants give a view of the essential cysteine residues for catalysis. Cd-MsrA combines a nucleophilic cysteine sulfenylation reaction with an intramolecular disulfide bond cascade linked to the thioredoxin pathway. Within this cascade, the oxidative equivalents are transferred to the surface of the protein while releasing the reduced substrate. Alternatively, MsrA catalyzes methionine sulfoxide reduction linked to the mycothiol/mycoredoxin-1 pathway. After the nucleophilic cysteine sulfenylation reaction, MsrA forms a mixed disulfide with mycothiol, which is transferred via a thiol disulfide relay mechanism to a second cysteine for reduction by mycoredoxin-1. With x-ray crystallography, we visualize two essential intermediates of the thioredoxin relay mechanism and a cacodylate molecule mimicking the substrate interactions in the active site. The interplay of both redox pathways in redox signaling regulation forms the basis for further research into the oxidative stress response of this pathogen.
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corynebacterium diphtheriae methionine sulfoxide reductase a exploits a unique mycothiol redox relay mechanism
Journal of Biological Chemistry, 2015Co-Authors: Mariaarmineh Tossounian, Brandan Pedre, Khadija Wahni, Huriye Erdogan, Didier Vertommen, Inge Van MolleAbstract:Methionine sulfoxide reductases are conserved enzymes that reduce oxidized methionines in proteins and play a pivotal role in cellular redox signaling. We have unraveled the redox relay mechanisms of methionine sulfoxide reductase A of the pathogen Corynebacterium diphtheriae (Cd-MsrA) and shown that this enzyme is coupled to two independent redox relay pathways. Steady-state kinetics combined with mass spectrometry of Cd-MsrA mutants give a view of the essential cysteine residues for catalysis. Cd-MsrA combines a nucleophilic cysteine sulfenylation reaction with an intramolecular disulfide bond cascade linked to the thioredoxin pathway. Within this cascade, the oxidative equivalents are transferred to the surface of the protein while releasing the reduced substrate. Alternatively, MsrA catalyzes methionine sulfoxide reduction linked to the mycothiol/mycoredoxin-1 pathway. After the nucleophilic cysteine sulfenylation reaction, MsrA forms a mixed disulfide with mycothiol, which is transferred via a thiol disulfide relay mechanism to a second cysteine for reduction by mycoredoxin-1. With x-ray crystallography, we visualize two essential intermediates of the thioredoxin relay mechanism and a cacodylate molecule mimicking the substrate interactions in the active site. The interplay of both redox pathways in redox signaling regulation forms the basis for further research into the oxidative stress response of this pathogen. Background: Methionine sulfoxide post-translational modifications have an important new signaling role in cells. Results: Methionine sulfoxide reductase MsrA of the pathogenic actinomycete Corynebacterium diphtheriae (Cd-MsrA) uses a unique intramolecular redox relay mechanism coupled to mycothiol. Conclusion: For methionine sulfoxide control, Cd-MsrA is flexible in receiving electrons from both the thioredoxin and the mycothiol pathways. Significance: C. diphtheriae MsrA is a redox regulator for methionine sulfoxide signaling.
Khadija Wahni - One of the best experts on this subject based on the ideXlab platform.
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disulfide bond formation protects arabidopsis thaliana glutathione transferase tau 23 from oxidative damage
Biochimica et Biophysica Acta, 2017Co-Authors: Mariaarmineh Tossounian, Khadija Wahni, Didier Vertommen, Inge Van Molle, Silke Jacques, Frank Van Breusegem, Kris Gevaert, David Young, Leonardo Astolfi Rosado, Joris MessensAbstract:Abstract Background Glutathione transferases play an important role as detoxifying enzymes. In A. thaliana, elevated levels of reactive oxygen species (ROS), provoked during biotic and abiotic stress, influence the activity of GSTU23. The aim of this study is to determine the impact of oxidative stress on the function and structure of GSTU23. Methods The impact of oxidation on the function of GSTU23 was studied using a glutathione transferase biochemical assay and mass spectrometry. With kinetics, circular dichroism and thermodynamics, we compared reduced with oxidized GSTU23. X-ray crystal structures of GSTU23 visualize the impact of oxidation on methionines and cysteines. Results In the presence of 100 μM H2O2, oxidation of the methionine side-chain to a sulfoxide is the prominent post-translational modification, which can be reduced by C. diphtheriae MsrA and MsrB. However, increasing the level to 200 μM H2O2 results in a reversible intramolecular disulfide between Cys65-Cys110, which is substrate for glutaredoxin. Under these oxidizing conditions, GSTU23 undergoes a structural change and forms a more favourable enzyme-substrate complex to overcome kcat decrease. Conclusions and significance At lower H2O2 levels (100 μM), GSTU23 forms methionine sulfoxides. Specifically, oxidation of Met14, located near the catalytic Ser13, could interfere with both GSH binding and catalytic activation. At higher H2O2 levels (200 μM), the Cys65-Cys110 disulfide bond protects other cysteines and also methionines from overoxidation. This study shows the impact of oxidative stress on GSTU23 regulated by methionine sulfoxide reductases and glutaredoxin, and the mechanisms involved in maintaining its catalytic functionality under oxidizing conditions.
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corynebacterium diphtheriae methionine sulfoxide reductase a exploits a unique mycothiol redox relay mechanism
Journal of Biological Chemistry, 2015Co-Authors: Mariaarmineh Tossounian, Brandan Pedre, Khadija Wahni, Huriye Erdogan, Didier Vertommen, Inge Van MolleAbstract:Methionine sulfoxide reductases are conserved enzymes that reduce oxidized methionines in proteins and play a pivotal role in cellular redox signaling. We have unraveled the redox relay mechanisms of methionine sulfoxide reductase A of the pathogen Corynebacterium diphtheriae (Cd-MsrA) and shown that this enzyme is coupled to two independent redox relay pathways. Steady-state kinetics combined with mass spectrometry of Cd-MsrA mutants give a view of the essential cysteine residues for catalysis. Cd-MsrA combines a nucleophilic cysteine sulfenylation reaction with an intramolecular disulfide bond cascade linked to the thioredoxin pathway. Within this cascade, the oxidative equivalents are transferred to the surface of the protein while releasing the reduced substrate. Alternatively, MsrA catalyzes methionine sulfoxide reduction linked to the mycothiol/mycoredoxin-1 pathway. After the nucleophilic cysteine sulfenylation reaction, MsrA forms a mixed disulfide with mycothiol, which is transferred via a thiol disulfide relay mechanism to a second cysteine for reduction by mycoredoxin-1. With x-ray crystallography, we visualize two essential intermediates of the thioredoxin relay mechanism and a cacodylate molecule mimicking the substrate interactions in the active site. The interplay of both redox pathways in redox signaling regulation forms the basis for further research into the oxidative stress response of this pathogen.
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corynebacterium diphtheriae methionine sulfoxide reductase a exploits a unique mycothiol redox relay mechanism
Journal of Biological Chemistry, 2015Co-Authors: Mariaarmineh Tossounian, Brandan Pedre, Khadija Wahni, Huriye Erdogan, Didier Vertommen, Inge Van MolleAbstract:Methionine sulfoxide reductases are conserved enzymes that reduce oxidized methionines in proteins and play a pivotal role in cellular redox signaling. We have unraveled the redox relay mechanisms of methionine sulfoxide reductase A of the pathogen Corynebacterium diphtheriae (Cd-MsrA) and shown that this enzyme is coupled to two independent redox relay pathways. Steady-state kinetics combined with mass spectrometry of Cd-MsrA mutants give a view of the essential cysteine residues for catalysis. Cd-MsrA combines a nucleophilic cysteine sulfenylation reaction with an intramolecular disulfide bond cascade linked to the thioredoxin pathway. Within this cascade, the oxidative equivalents are transferred to the surface of the protein while releasing the reduced substrate. Alternatively, MsrA catalyzes methionine sulfoxide reduction linked to the mycothiol/mycoredoxin-1 pathway. After the nucleophilic cysteine sulfenylation reaction, MsrA forms a mixed disulfide with mycothiol, which is transferred via a thiol disulfide relay mechanism to a second cysteine for reduction by mycoredoxin-1. With x-ray crystallography, we visualize two essential intermediates of the thioredoxin relay mechanism and a cacodylate molecule mimicking the substrate interactions in the active site. The interplay of both redox pathways in redox signaling regulation forms the basis for further research into the oxidative stress response of this pathogen. Background: Methionine sulfoxide post-translational modifications have an important new signaling role in cells. Results: Methionine sulfoxide reductase MsrA of the pathogenic actinomycete Corynebacterium diphtheriae (Cd-MsrA) uses a unique intramolecular redox relay mechanism coupled to mycothiol. Conclusion: For methionine sulfoxide control, Cd-MsrA is flexible in receiving electrons from both the thioredoxin and the mycothiol pathways. Significance: C. diphtheriae MsrA is a redox regulator for methionine sulfoxide signaling.
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protein methionine sulfoxide dynamics in arabidopsis thaliana under oxidative stress
Molecular & Cellular Proteomics, 2015Co-Authors: Silke Jacques, Khadija Wahni, Bart Ghesquiere, Pieterjan De Bock, Hans Demol, Patrick Willems, Joris Messens, Frank Van Breusegem, Kris GevaertAbstract:Reactive oxygen species such as hydrogen peroxide can modify proteins via direct oxidation of their sulfur-containing amino acids, cysteine and methionine. Methionine oxidation, studied here, is a reversible posttranslational modification that is emerging as a mechanism by which proteins perceive oxidative stress and function in redox signaling. Identification of proteins with oxidized methionines is the first prerequisite toward understanding the functional effect of methionine oxidation on proteins and the biological processes in which they are involved. Here, we describe a proteome-wide study of in vivo protein-bound methionine oxidation in plants upon oxidative stress using Arabidopsis thaliana catalase 2 knock-out plants as a model system. We identified over 500 sites of oxidation in about 400 proteins and quantified the differences in oxidation between wild-type and catalase 2 knock-out plants. We show that the activity of two plant-specific glutathione S-transferases, GSTF9 and GSTT23, is significantly reduced upon oxidation. And, by sampling over time, we mapped the dynamics of methionine oxidation and gained new insights into this complex and dynamic landscape of a part of the plant proteome that is sculpted by oxidative stress.
Rodney L. Levine - One of the best experts on this subject based on the ideXlab platform.
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drosophila methionine sulfoxide reductase a is not a methionine oxidase
Free Radical Biology and Medicine, 2017Co-Authors: Sreya Tarafdar, Nasser M. Rusan, Rodney L. LevineAbstract:Methionine sulfoxide reductase A (MsrA) stereospecifically catalyzes the reduction of S-methionine sulfoxide to methionine and is important in defense against oxidative stress. Recently, we reported that mammalian methionine sulfoxide reductase A stereospecifically and selectively oxidizes Met77 in calcium-bound calmodulin and can fully reduce it as well. The control mechanism that prevents futile cycling is hypothesized to be through interaction with a postulated regulatory protein. Thus, cyclic oxidation and reduction of methionines in proteins by MsrA could function as a redox-based mechanism of cellular regulation. Our aim in this study was to elucidate the physiological significance of methionine sulfoxide reductase A mediated reversible oxidation of calmodulin Met77 in Drosophila. However, we found that Drosophila MsrA, unlike its mammalian counterpart, is not a methionine oxidase. This led us to explore the mechanistic details of the enzyme. Using a double alkylation approach with HPLC-mass spectrometric sequencing, we found that the active site cysteine residue in Drosophila MsrA becomes locked in a disulfide bond with the terminal cysteine residue of the protein and thus cannot mediate oxidation. A mutant Drosophila MsrA lacking the two C-terminal cysteine residues also lacked oxidase activity, despite not being able to form a disulfide bond with the active site cysteine.
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stereospecific oxidation of calmodulin by methionine sulfoxide reductase a
Free Radical Biology and Medicine, 2013Co-Authors: Rodney L. LevineAbstract:Abstract Methionine sulfoxide reductase A has long been known to reduce S -methionine sulfoxide, both as a free amino acid and within proteins. Recently the enzyme was shown to be bidirectional, capable of oxidizing free methionine and methionine in proteins to S -methionine sulfoxide. A feasible mechanism for controlling the directionality has been proposed, raising the possibility that reversible oxidation and reduction of methionine residues within proteins is a redox-based mechanism for cellular regulation. We undertook studies aimed at identifying proteins that are subject to site-specific, stereospecific oxidation and reduction of methionine residues. We found that calmodulin, which has nine methionine residues, is such a substrate for methionine sulfoxide reductase A. When calmodulin is in its calcium-bound form, Met77 is oxidized to S -methionine sulfoxide by methionine sulfoxide reductase A. When methionine sulfoxide reductase A operates in the reducing direction, the oxidized calmodulin is fully reduced back to its native form. We conclude that reversible covalent modification of Met77 may regulate the interaction of calmodulin with one or more of its many targets.
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methionine sulfoxide reductase a is a stereospecific methionine oxidase
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: Rodney L. LevineAbstract:Methionine sulfoxide reductase A (MsrA) catalyzes the reduction of methionine sulfoxide to methionine and is specific for the S epimer of methionine sulfoxide. The enzyme participates in defense against oxidative stresses by reducing methionine sulfoxide residues in proteins back to methionine. Because oxidation of methionine residues is reversible, this covalent modification could also function as a mechanism for cellular regulation, provided there exists a stereospecific methionine oxidase. We show that MsrA itself is a stereospecific methionine oxidase, producing S-methionine sulfoxide as its product. MsrA catalyzes its own autooxidation as well as oxidation of free methionine and methionine residues in peptides and proteins. When functioning as a reductase, MsrA fully reverses the oxidations which it catalyzes.
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oxidation of either methionine 351 or methionine 358 in alpha 1 antitrypsin causes loss of anti neutrophil elastase activity
Journal of Biological Chemistry, 2000Co-Authors: Clifford C Taggart, Daniel Cervanteslaurean, Noel G Mcelvaney, Nancy B Wehr, Joel Moss, Rodney L. LevineAbstract:Abstract Hydrogen peroxide is a component of cigarette smoke known to be essential for inactivation of α1-antitrypsin, the primary inhibitor of neutrophil elastase. To establish the molecular basis of the inactivation of α1-antitrypsin, we determined the sites oxidized by hydrogen peroxide. Two of the nine methionines were particularly susceptible to oxidation. One was methionine 358, whose oxidation was known to cause loss of anti-elastase activity. The other, methionine 351, was as susceptible to oxidation as methionine 358. Its oxidation also resulted in loss of anti-elastase activity, an effect not previously recognized. The equal susceptibility of methionine 358 and methionine 351 to oxidation was confirmed by mass spectrometry. To verify this finding, we produced recombinant α1-antitrypsins in which one or both of the susceptible methionines were mutated to valine. M351V and M358V were not as rapidly inactivated as wild-type α1-antitrypsin, but only the double mutant M351V/M358V was markedly resistant to oxidative inactivation. We suggest that inactivation of α1-antitrypsin by oxidation of either methionine 351 or 358 provides a mechanism for regulation of its activity at sites of inflammation.
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methionine residues may protect proteins from critical oxidative damage
Mechanisms of Ageing and Development, 1999Co-Authors: Rodney L. Levine, Jackob Moskovitz, Barbara S Berlett, Laurent Mosoni, Earl R StadtmanAbstract:Cysteine and methionine are the two sulfur-containing residues normally found in proteins. Cysteine residues function in the catalytic cycle of many enzymes, and they form disulfide bonds which contribute to protein structure. In contrast, the key functions of methionine residues are not known. We propose that methionine residues constitute an important antioxidant defense mechanism. A variety of oxidants react readily with methionine to form methionine sulfoxide, and surface exposed methionine residues create an extremely high concentration of reactant, providing for efficient scavenging of oxidants. The effect of hydrogen peroxide exposure upon glutamine synthetase from Escherichia coli was studied as an in vitro model system. Eight of the sixteen methionine residues could be oxidized with little effect on activity. The oxidizable methionine residues were found to be relatively surface exposed while the intact residues were generally buried within the core of the protein. Further, the susceptible residues were physically arranged in an array which guarded the entrance to the active site. Methionine sulfoxide can be reduced back to methionine by the enzyme methionine sulfoxide reductase, providing a catalytic amplification of the antioxidant potential of each methionine residue. Given the importance of oxidative stress during aging, the potential function of methionine residues as antioxidants during aging should be investigated experimentally.
Anastasia Korlimbinis - One of the best experts on this subject based on the ideXlab platform.
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3 hydroxykynurenine oxidizes alpha crystallin potential role in cataractogenesis
Biochemistry, 2006Co-Authors: Anastasia Korlimbinis, Roger J W Truscott, Peter G Hains, Andrew AquilinaAbstract:The alpha-, beta-, and gamma-crystallins are the major structural proteins of mammalian lenses. The human lens also contains tryptophan-derived UV filters, which are known to spontaneously deaminate at physiological pH and covalently attach to lens proteins. 3-Hydroxykynurenine (3OHKyn) is the third most abundant of the kynurenine UV filters in the lens, and previous studies have shown this compound to be unstable and to be oxidized under physiological conditions, producing H2O2. In this study, we show that methionine and tryptophan amino acid residues are oxidized when bovine alpha-crystallin is incubated with 3-hydroxykynurenine. We observed almost complete oxidation of methionines 1 and 138 in alphaA-crystallin and a similar extent of oxidation of methionines 1 and 68 in alphaB-crystallin after 48 h. Tryptophans 9 and 60 in alphaB-crystallin were oxidized to a lesser extent. AlphaA-crystallin was also found to have 3OHKyn bound to its single cysteine residue. Examination of normal aged human lenses revealed no evidence of oxidation of alpha-crystallin; however, oxidation was detected at methionine 1 in both alphaA- and alphaB-crystallin from human cataractous lenses. Age-related nuclear cataract is associated with coloration and insolubilization of lens proteins and extensive oxidation of cysteine and methionine residues. Our findings demonstrate that 3-hydroxykynurenine can readily catalyze the oxidation of methionine residues in both alphaB- and alphaA-crystallin, and it has been reported that alpha-crystallin modified in this way is a poorer chaperone. Thus, 3-hydroxykynurenine promotes the oxidation and modification of crystallins and may contribute to oxidative stress in the human lens.
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3 hydroxykynurenine oxidizes alpha crystallin potential role in cataractogenesis
Biochemistry, 2006Co-Authors: Roger J W Truscott, Andrew Aquilina, Peter G Hains, Anastasia KorlimbinisAbstract:The α-, β-, and γ-crystallins are the major structural proteins of mammalian lenses. The human lens also contains tryptophan-derived UV filters, which are known to spontaneously deaminate at physiological pH and covalently attach to lens proteins. 3-Hydroxykynurenine (3OHKyn) is the third most abundant of the kynurenine UV filters in the lens, and previous studies have shown this compound to be unstable and to be oxidized under physiological conditions, producing H2O2. In this study, we show that methionine and tryptophan amino acid residues are oxidized when bovine α-crystallin is incubated with 3-hydroxykynurenine. We observed almost complete oxidation of methionines 1 and 138 in αA-crystallin and a similar extent of oxidation of methionines 1 and 68 in αB-crystallin after 48 h. Tryptophans 9 and 60 in αB-crystallin were oxidized to a lesser extent. αA-Crystallin was also found to have 3OHKyn bound to its single cysteine residue. Examination of normal aged human lenses revealed no evidence of oxidation ...
Andrew Aquilina - One of the best experts on this subject based on the ideXlab platform.
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3 hydroxykynurenine oxidizes alpha crystallin potential role in cataractogenesis
Biochemistry, 2006Co-Authors: Anastasia Korlimbinis, Roger J W Truscott, Peter G Hains, Andrew AquilinaAbstract:The alpha-, beta-, and gamma-crystallins are the major structural proteins of mammalian lenses. The human lens also contains tryptophan-derived UV filters, which are known to spontaneously deaminate at physiological pH and covalently attach to lens proteins. 3-Hydroxykynurenine (3OHKyn) is the third most abundant of the kynurenine UV filters in the lens, and previous studies have shown this compound to be unstable and to be oxidized under physiological conditions, producing H2O2. In this study, we show that methionine and tryptophan amino acid residues are oxidized when bovine alpha-crystallin is incubated with 3-hydroxykynurenine. We observed almost complete oxidation of methionines 1 and 138 in alphaA-crystallin and a similar extent of oxidation of methionines 1 and 68 in alphaB-crystallin after 48 h. Tryptophans 9 and 60 in alphaB-crystallin were oxidized to a lesser extent. AlphaA-crystallin was also found to have 3OHKyn bound to its single cysteine residue. Examination of normal aged human lenses revealed no evidence of oxidation of alpha-crystallin; however, oxidation was detected at methionine 1 in both alphaA- and alphaB-crystallin from human cataractous lenses. Age-related nuclear cataract is associated with coloration and insolubilization of lens proteins and extensive oxidation of cysteine and methionine residues. Our findings demonstrate that 3-hydroxykynurenine can readily catalyze the oxidation of methionine residues in both alphaB- and alphaA-crystallin, and it has been reported that alpha-crystallin modified in this way is a poorer chaperone. Thus, 3-hydroxykynurenine promotes the oxidation and modification of crystallins and may contribute to oxidative stress in the human lens.
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3 hydroxykynurenine oxidizes alpha crystallin potential role in cataractogenesis
Biochemistry, 2006Co-Authors: Roger J W Truscott, Andrew Aquilina, Peter G Hains, Anastasia KorlimbinisAbstract:The α-, β-, and γ-crystallins are the major structural proteins of mammalian lenses. The human lens also contains tryptophan-derived UV filters, which are known to spontaneously deaminate at physiological pH and covalently attach to lens proteins. 3-Hydroxykynurenine (3OHKyn) is the third most abundant of the kynurenine UV filters in the lens, and previous studies have shown this compound to be unstable and to be oxidized under physiological conditions, producing H2O2. In this study, we show that methionine and tryptophan amino acid residues are oxidized when bovine α-crystallin is incubated with 3-hydroxykynurenine. We observed almost complete oxidation of methionines 1 and 138 in αA-crystallin and a similar extent of oxidation of methionines 1 and 68 in αB-crystallin after 48 h. Tryptophans 9 and 60 in αB-crystallin were oxidized to a lesser extent. αA-Crystallin was also found to have 3OHKyn bound to its single cysteine residue. Examination of normal aged human lenses revealed no evidence of oxidation ...
