J. Biol. Chem., Vol. 262, Issue 32, 15545-15551, 11, 1987
Inter- and intramolecular disulfide bond formation and related structural changes in the lens proteins. A Raman spectroscopic study in vivo of lens aging
Y Ozaki, A Mizuno, K Itoh and K Iriyama
Division of Biochemistry, Jikei University School of Medicine, Tokyo, Japan.
Raman spectra have been measured for intact rat lens nuclei at various
stages of aging in an attempt to gain further insight into age-related
structural changes in the lens proteins, especially changes concerning
protein sulfhydryl groups. Two Raman bands at 2579 and 2561 cm-1 were
observed to be assignable to SH stretching modes of the cysteine residues.
These bands have been attributed to "exposed" and "buried" sulfhydryl
groups of the lens proteins, respectively, on the basis of a model compound
study. The relative intensities of both SH stretching modes decreased with
lens aging, and concurrently the intensity of a S- S stretching mode at 509
cm-1 due to disulfide bridges increased, suggesting that not only exposed
but also buried protein sulfhydryl groups are converted to disulfide groups
as a result of aging. The rate of the intensity decrease in the 2561 cm-1
band was similar to that in the 2579 cm-1 band. Therefore, it seems likely
that the sulfhydryl groups in the two distinct environments are nearly
equally subjected to the oxidation. Cysteine and cystine residues of the
lens proteins gave their C-S stretching modes at 708 cm-1, indicating that
they predominantly assume PC and/or PN conformers. The intensity ratio of a
tyrosine doublet near 840 cm-1 (I832/I855) changed from approximately 0.86
to approximately 0.81 with the aging of the rat lens. This result implies
that some tyrosine residues undergo a change in their hydrogen bonding
environments during the course of aging. Of particular importance is that
the relative intensity change of the tyrosine doublet with normal aging and
that with cataract formation are in opposite directions.