Composition and synthesis in vivo of water-soluble proteins in the rat ocular lens: normal and cataractous

This study describes the composition and synthesis in vivo of the water-insoluble proteins in normal and cataractous rat ocular lens. Cataracts of the lens nucleus were induced by treatment of the young rat with U18666A, 3β-(2-diethylaminoethoxy)androst-5-en-17-one. HCl. Opaque lens contained more insoluble proteins and incorporated more intraocularly injected [³H]leucine into these proteins than clear lens. Insoluble proteins from both clear and opaque lens consisted of classes in three mol. wt. ranges; > 68 000, 35 000–60 000 and 16 000–22 000. Treatment with mercaptoethanol produced changes in the electrophoretic profiles of the 35 000–60 000 and 16 000–22 000 mol. wt. classes of proteins from both normal and opaque lens; however, the higher mol. wt. class from only the opaque lens was reduced to smaller components. The lowest mol. wt. class accounted for over 50% of the total water-insoluble protein in both types of lens. [³H]leucine was incorporated into the protein classes roughly proportionate to their relative concentrations, although there was a tendency for normal lens to incorporate more label into peak 1 and 2 proteins and for cataractous lens to incorporate more into peak 3 proteins. In general, however, the greater concentration of water-insoluble protein in this cataract appeared due to a proportionately increased formation of the same proteins present in normal lens. In contrast to human senile cataracts, the opaque rat lens did not preferentially accumulate disulfidelinked very high mol. wt. insoluble protein. However, the aged (i.e. pre-existing) higher mol. wt. insoluble proteins of the U18666A cataract appeared different from those newly synthesized, since the aged proteins were reduced under conditions not affecting those newly synthesized.