Photooxidation of the nonenzymatic browning products in calf lens alpha-crystallin

The browning reaction (or advanced glycation) of calf lens alpha-crystallin generates chromophores which absorb light at wavelengths above 300 nm. They display an absorption shoulder above 300 nm, a positive circular dichroism band at 320-340 nm, and a blue fluorescence at 460 nm (Ex = 370 nm). Upon irradiation by UV-A light at a wavelength of 320-350 nm, the intensity of the absorption shoulder displayed an increase, but both circular dichroism and blue fluorescence intensities decreased. It appears that browning chromophores were photolyzed and converted to species which absorb more light at 320-330 nm, but are optically inactive. The browning products are thus susceptible to photooxidation from radiation of light above 300 nm and add an oxidative stress to the lens proteins.