Galactose-induced cataract in rat: Raman detection of sulfhydryl decrease and water increase along an equatorial diameter

Raman spectroscopy shows that maturation of galactose cataract greatly increases the water signal (at 3417 cm^-1) which is correlated with the imbibition of water in the lens. The maximum water: protein ratio (expressed as Raman intensity ratio I₃₄₁₇:I₂₉₃₆) occurs at the peripheral cortex (i.e.≈4·7), which is much higher than the ratios found in Emory cataract (≈0·3) and in cac-strain mouse cataract (≈0·5). It is demonstrated that Raman measurement of the intensity ratio I₃₄₁₇:I₂₉₃₆ is a more sensitive way to reflect increase of water in cataract, compared to water concentration (percentage of wet weight of the lens). The small decrease in the sulfhydryl profile along an equatorial diameter is attributed to the concentration decrease in glutathione. There is no spectroscopic evidence for extensive disulfide bond formation associated with galactosemic cataractogenesis in rat. There is an increase in the tyrosine I₈₃₂:I₈₅₈ ratio (normal 1·74; cataract 3·43), indicating a strengthening of the phenolic hydrogen bond, a change which has been found in Raman spectra of all cataracts studied. A comparison of the Raman spectra of normal lenses and mature cataracts reveals no change in conformation of the protein backbone.