Age-dependent covalent changes in MP18 from bovine lens membrane.

Peptide antisera made against the putative MP18 sequence recognizes an 18-kilodalton protein on western blots of bovine lens membrane. These peptide antisera were used to investigate possible age-related changes in the MP18 molecule in membrane fractions from newborn and adult bovine lenses. Western blot analysis of membrane fractions with peptide antisera to sequences 45-50 (anti-45), 113-129 (anti-113), and C-terminus 169-173 (anti-Ct) showed similar patterns. All three antisera reacted more strongly with MP18 from membrane prepared from newborn lenses than with corresponding preparations from the adult lens. Binding ratios of anti-45 to anti-Ct showed a statistically significant difference between cortex and nucleus of newborn lenses (P less than 0.02) and between cortex of newborn and cortex of adult lenses (P less than 0.001). Differences in binding ratios of anti-113 to anti-Ct were the most striking, with anti-113 unable to detect MP18 in membrane preparations from adult lenses. Collectively, these results confirmed the putative sequence of MP18 and demonstrated covalent changes in this molecule during the process of aging in the normal bovine lens.