Glutathione and NADH, but not ascorbate, protect lens proteins from modification by UV filters

Lisa M. Taylor, J. Andrew Aquilina, Joanne F. Jamie, Roger J W Truscott

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Age-dependent human lens colouration and fluorescence may stem primarily from the covalent binding of UV filters to crystallins. The tendency of the kynurenine (Kyn) UV filters to deaminate at neutral pH, with the generation of reactive α,β-ketoalkenes, underlies this phenomenon. In this study the authors examined the ability of small molecular weight antioxidants, which are known to be present in the lens, to inhibit this process. Crystallins were incubated with Kyn at pH 7 in the presence of glutathione (GSH), ascorbate or NADH. Ascorbate, even at high (15 mM) levels, was not found to significantly retard the time-dependent covalent binding of Kyn to the proteins. GSH, and to a lesser extent NADH, however, had a major impact in preventing this modification. The increase in protein UV absorbance and fluorescence was inhibited by GSH intercepting the reactive ketone intermediate, to form a GSH-Kyn adduct. NADH seemed to protect by both reduction of the reactive ketone intermediate and by competing with Kyn for presumably hydrophobic sites on the crystallins. This may indicate that the covalent attachment of aromatic Kyn molecules could be facilitated by initial hydrophobic interactions. Since GSH is present at far greater concentrations than NADH, these results show that in primate lenses, GSH is the key agent responsible for protecting the crystallins from covalent modification.

LanguageEnglish
Pages503-511
Number of pages9
JournalExperimental Eye Research
Volume74
Issue number4
DOIs
Publication statusPublished - 2002

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Kynurenine
Crystallins
NAD
Glutathione
Lenses
Ketones
Fluorescence
Hydrophobic and Hydrophilic Interactions
Primates
Proteins
Antioxidants
Molecular Weight

Cite this

Taylor, Lisa M. ; Andrew Aquilina, J. ; Jamie, Joanne F. ; Truscott, Roger J W. / Glutathione and NADH, but not ascorbate, protect lens proteins from modification by UV filters. In: Experimental Eye Research. 2002 ; Vol. 74, No. 4. pp. 503-511.
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abstract = "Age-dependent human lens colouration and fluorescence may stem primarily from the covalent binding of UV filters to crystallins. The tendency of the kynurenine (Kyn) UV filters to deaminate at neutral pH, with the generation of reactive α,β-ketoalkenes, underlies this phenomenon. In this study the authors examined the ability of small molecular weight antioxidants, which are known to be present in the lens, to inhibit this process. Crystallins were incubated with Kyn at pH 7 in the presence of glutathione (GSH), ascorbate or NADH. Ascorbate, even at high (15 mM) levels, was not found to significantly retard the time-dependent covalent binding of Kyn to the proteins. GSH, and to a lesser extent NADH, however, had a major impact in preventing this modification. The increase in protein UV absorbance and fluorescence was inhibited by GSH intercepting the reactive ketone intermediate, to form a GSH-Kyn adduct. NADH seemed to protect by both reduction of the reactive ketone intermediate and by competing with Kyn for presumably hydrophobic sites on the crystallins. This may indicate that the covalent attachment of aromatic Kyn molecules could be facilitated by initial hydrophobic interactions. Since GSH is present at far greater concentrations than NADH, these results show that in primate lenses, GSH is the key agent responsible for protecting the crystallins from covalent modification.",
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Glutathione and NADH, but not ascorbate, protect lens proteins from modification by UV filters. / Taylor, Lisa M.; Andrew Aquilina, J.; Jamie, Joanne F.; Truscott, Roger J W.

In: Experimental Eye Research, Vol. 74, No. 4, 2002, p. 503-511.

Research output: Contribution to journalArticleResearchpeer-review

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