EFFECT OF UVB RADIATION ON CORNEAL ALDEHYDE DEHYDROGENASE

Purpose. A Class 3 aldehyde dehydrogenase happens to be a major solubl e protein constituent of the cornea. Its role is conjectured to be man ifold: to protect the tissue from oxidative damage by eliminating the toxic aldehydes produced upon lipid peroxidation under oxidative stres s, to act as an UV-absorber, and to maintain the level of the coenzyme NADH in the cornea. We have studied the effect of UVB on the structur e and enzyme activity of corneal aldehyde dehydrogenase. Methods. Alde hyde dehydrogenase was irradiated at 295 nm for varying periods of tim e and change in its enzyme activity assayed. The structural changes in the molecule accompanying irradiation were monitored using fluorescen ce and circular dichroism spectroscopy, and its hydrodynamic behavior and surface hydrophobicity studied using gel filtration chromatography and binding of the hydrophobic fluorophore ANS. The protective abilit y of aldehyde dehydrogenase in preventing aggregation of photolabile p roteins, such as Gamma-crystallin of the eye lens, was studied by moni toring the scattering value of the test protein with irradiation by UV B. Results. Aldehyde dehydrogenase is seen to undergo photodamage with alterations in its quaternary structure, though no significant change is noticed in the peptide chain conformation. Under such conditions t he molecule continues to act as a protectant by preventing aggregation of photolabile proteins such as the eye lens Gamma-crystallin. Conclu sions. Our earlier studies have shown that the free sulfhydryl groups are important for the antioxidant abilities of aldehyde dehydrogenase. Its protective ability towards photoaggregation of Gamma-crystallin s een here might arise both due to: (i) oxyradical quenching and (ii) th e increased surface hydrophobicity of the molecule upon irradiation, w hich allows it to bind to, and thus inhibit the aggregation of interac ting proteins.