A temporal and spatial study of the synthesis and degradation of water-soluble and insoluble proteins in galactosemic rat lenses

Abstract

Events of synthesis and degradation of water-soluble and -insoluble rat lens proteins were examined during a 21-day period of galactose-induced cataractogenesis. Epithelial cells continued to synthesize both fractions of proteins throughout the duration of the experiment. There were few qualitative changes in the pattern of proteins expressed and the rate of synthesis did not decrease. In contrast, synthesis of both water-soluble and -insoluble proteins by the cortical cells decreased and then became totally inhibited indicating no selective or differential inhibition of synthesis of one protein fraction, but that both water-soluble and -insoluble proteins in the cortical cells are equally affected by the metabolic changes associated with galactose-induced cataractogenesis. The cells within the nuclear region of control lenses were capable of incorporating [35S]-methionine into protein. This synthesis was completely abolished in 7- and 14-day nuclear cells. Labeled proteins were found to be present in the 21-day nuclear preparation to a level almost three times greater than that observed in the control nucleus. Degradation was minimal in both fractions of epithelial proteins, whereas selective degradation of proteins from both fractions was apparent in 14- and 21-day cortical cells. At day 14, the water-soluble protein profile from nuclear cells became less complex with the loss of several major bands, but these bands as well as some unique bands appeared at day 21. The profile of water-insoluble nuclear proteins remained unchanged over 21 days.