Front surface fluorometric study of lens insoluble proteins

Although the quantity of insoluble lens proteins increases with aging and cataracts, it is unknown whether the quality, such as protein structure, also changes correspondingly. In this study front surface fluorometry was used to study powdered samples of insoluble proteins isolated from young calf and old cow lenses, as well as from young clear and old cataractous human lenses. Tryptophan (Trp) fluorescence shows that there is a difference in protein conformation between young and old bovine samples. The old sample appears to have more open structure. This is demonstrated by a red shift in Trp emission maxima. The water-insoluble fraction shows 3-4 nm shift, while its urea-soluble and urea-insoluble fraction show 1-2 nm shift. The unfoldedness found in soluble crystallins is thus retained when they become insoluble. Both young and old human insoluble samples give a long Trp emission wavelength without showing any difference. Another major change that can be measured by fluorescence is the appearance of the 370/440 nm peak in old bovine insoluble powdered samples. Human samples also give this peak, and its position shifts to a longer wavelength in senile lenses.