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.
| Language | English |
|---|---|
| Pages | 503-511 |
| Number of pages | 9 |
| Journal | Experimental Eye Research |
| Volume | 74 |
| Issue number | 4 |
| DOIs | |
| Publication status | Published - 2002 |
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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 journal › Article › Research › peer-review
TY - JOUR
T1 - Glutathione and NADH, but not ascorbate, protect lens proteins from modification by UV filters
AU - Taylor, Lisa M.
AU - Andrew Aquilina, J.
AU - Jamie, Joanne F.
AU - Truscott, Roger J W
PY - 2002
Y1 - 2002
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=0036315485&partnerID=8YFLogxK
U2 - 10.1006/exer.2001.1165
DO - 10.1006/exer.2001.1165
M3 - Article
VL - 74
SP - 503
EP - 511
JO - Experimental Eye Research
T2 - Experimental Eye Research
JF - Experimental Eye Research
SN - 0014-4835
IS - 4
ER -