Raman spectroscopic study of age-related structural changes in the lens proteins of an intact mouse lens

Age-related structural changes in the lens proteins of a normal mouse lens have been monitored in situ by laser Raman spectroscopy. The Raman spectrum of an ICR-strain mouse lens nucleus showed virtually no change in the 550-850- and 900-1800-cm-1 regions as the mouse aged. Lens aging, however, did cause a significant intensity decrease of the Raman band at 880 cm-1 due to tryptophan residues, and the intensity decrease seems to be stepwise. This observation implies that a microenvironmental change of tryptophan residues takes place twice at different places of the lens proteins during normal aging. Particularly striking is that the intensity decrease of the band at 880 cm-1 proceeds in parallel with that of the Raman band at 2579 cm-1 due to a SH stretching mode for the first 4 months. Thus, the first microenvironmental change of tryptophan residues seems to be correlated with the formation of S-S bonds. In contrast to tryptophan residues, no evidence was observed of a microenvironmental change in tyrosine residues. In this respect, the structural changes of lens proteins in aging are sharply distinct from those in lens opacification, in which tyrosine as well as tryptophan residues undergo microenvironmental changes [Itoh, K., Ozaki, Y., Mizuno, A., & Iriyama, K. (1983) Biochemistry 22, 1773-1778]. The relative intensity of the band at 3390 cm-1 due to an OH stretching mode of lens water fell rapidly for the first 4 months and then decreased very gradually. The observation clearly exhibits the process of lens dehydration.(ABSTRACT TRUNCATED AT 250 WORDS)