Age-related changes in a fiber cell-specific extrinsic membrane protein.

Western blot analysis using a monoclonal antibody raised against a lens fiber cell-specific, extrinsic membrane protein reveals several immunologically related bands in fractions derived from bovine lens. Previous work suggests that the parent molecule is the Mr 115 species, and that lower molecular weight bands represent the products of a progressive, step-wise, post-translational degradation. In this report we compare the extent of proteolytic degradation in extracts prepared from the lens cortex and lens nucleus, using both protease-suppressive and protease-permissive isolation protocols. The results suggest that the observed degradation is a result of in vivo post-translational modification of the Mr 115 antigen, and thus represents physiologic aging of this protein. This analysis also suggests that degradation alters the solubility and/or membrane affinity of this antigen, resulting in a progressive shift to the insoluble phase.