FT-Raman spectroscopic investigation of lens proteins of tilapia treated with dietary vitamin E

FT-Raman spectroscopy was employed to explore the structural changes of lens proteins in Tilapia lenses affected by dietary vitamin E supplementation. The microenvironment of major lens constituents including thiol compounds, tyrosine, and tryptophan exhibited significant change upon vitamin E treatment, while the protein secondary structure was unaltered and remained as an antiparallel β-pleated sheet. These structures in the cortex were more susceptible to vitamin E treatment than in the nucleus. Protein sulfhydryls in the cortex were predominantly in the reduced form, while in the nucleus both the oxidized and reduced forms coexisted as evidenced by the vibrational mode of SH (2580 cm−1) and SS (507 cm−1), respectively. Both tyrosine and tryptophan were more accessible to water or more exposed in the cortex than in the nucleus. The symmetrically inverse response of vitamin E, between Raman intensity of 1090 cm−1 and the glutathione level, was consistent with a close relationship of GSH and vitamin E in defending the lens from external insults.