Covalent change in alpha crystallin in opaque and transparent sections from the same human cataractous lens.

Opaque and transparent regions from the cortex of the same human cataractous lens were removed, and the water soluble proteins from these sections were resolved by isoelectric focusing in the presence of 8M urea, followed by Western blot analysis using antisera to the whole alpha crystallin molecule. Analysis of 18 different sections from 3 different lens demonstrated statistically significant changes in the charge distribution of alpha crystallins between opaque and transparent sections, with the greatest changes occurring in the anterior, posterior and equatorial sections from a 66-year-old cataractous lens. All opaque sections from this lens contained alpha crystallin with more positive charge than the transparent sections from the same lens. This change was present in both the water soluble and the insoluble fractions of the microdissected sections, and could also be demonstrated by probing of the Western blots with antisera made against synthetic peptides corresponding to the N-terminal and C-terminal regions of the molecule. Together, these results demonstrate that during human senile cataractogenesis there is often a covalent modification of the alpha crystallin molecule, which is probably not due to simple proteolysis, and which results in a shift of the alpha crystallin molecule to a more basic form.