Action spectrum for photocross-linking of human lens proteins

The action spectrum for photocross-linking was measured for human lens beta gamma-crystallins from young adult noncataractous lenses at wavelengths of 297, 302, 313, 334 and 365 nm. The action spectrum had a maximal effectiveness at 297 nm that sharply decreased in effectiveness up to 313 nm, then remained flat until 334 nm and decreased markedly as wavelength increased to 365 nm. Radiation at 297 nm was 36 times more effective in producing cross-linking than 302 nm radiation. The 297 nm radiation was 220, 195 and 1300 times more effective than 313, 334 and 365 nm radiation, respectively. The action spectrum had a shape similar to the absorption spectrum of the lens proteins but the response was lower than expected from the absorption data, suggesting that some of the absorptions are not effective at cross-linking. Because most animal experimentation and epidemiological studies include broadband radiation, these studies would be useful in predicting the biological response of the lens to environmental UV stress.