A. Kaminska et al., A comparative study of the effect of exogenous and endogenous photostabilizers on lens crystallin photodegradation, J FLUORESC, 9(3), 1999, pp. 213-219
The purpose of the present study was to determine in vitro the effect of so
dium azide, ethanol, trans-beta-carotene, and the reduced form of glutathio
ne on phototransformations in the lens crystallin. These photostabilizers s
how a specific affinity for different kinds of free radicals. The water-sol
uble protein from the cortical part of the eye was irradiated with doses of
UV C ranging from 0 to 4.07 J/cm(2). Changes in the structure of the cryst
allins have been monitored by steady-state absorption and fluorescence spec
troscopy. Irradiation of dialyzed samples of these proteins at a wavelength
of 254 nm (1.13 +/- 0.02 mW/cm(2)) caused photooxidation of aromatic resid
ues; the crystallin solutions became opaque and turbid. The samples display
ed increasing attenuance at a wavelength of 280 nm as photodamage proceeded
. The fluorescence of tryptophan at 333 nm systematically decreased and a n
ew band between 400 and 500 nm appeared during the UV C irradiation. Our re
sults show that the antioxidants can protect proteins from UV C-induced pho
todegradation and the protective effect is significantly dependent on their
concentration in the protein solution. There are no dramatic differences i
n the rates of exogenous and endogenous scavenging of generated free radica
ls for all concentrations used, with rate constants varying by a factor no
greater than 2. The mechanism and the rate of scavenging or quenching are d
ependent on the nature of the radical species and the photostabilizer struc
ture. Although this study provides evidence for free radical scavenging and
protein protection, extrapolations to possible antioxidant effects in vivo
must be made cautiously.