Calcium-induced high molecular weight proteins in the intact rabbit lens

We have investigated the ability of Ca2+ to induce the formation of high molecular weight (HMW) proteins in the intact lens. Ca2+ cataracts were produced in rabbit lenses by culturing the lenses for either four days in medium containing 20 mM Ca2+ or for three days in medium containing 100 mM Ca2+. Lenses cultured in 20 and 100 mM Ca2+ medium became opaque after 20 hr and contained 30 and 200 times higher levels of Ca2+, respectively, than transparent lenses cultured in medium containing 1 mM Ca2+. Lenses exposed to 100 mM Mg2+ did not lose transparency. The opacification of the lenses extended to a depth of 1 mm into the cortical layer and did not involve the nucleus. No significant differences were found in the concentrations of either soluble or insoluble proteins present in freshly excised lenses and Ca2+ cataracts. Soluble HMW proteins, greater than 1.5 X 10(6) daltons, were in two- and five-fold greater amounts in the 20 and 100 mM Ca2+ cataracts, respectively, compared to controls. HMW protein present in the 100 mM Ca2+ cataract amounted to approximately 3% of the total soluble protein in the lens. The amount of Ca2+ present in the HMW fraction was 1 Ca2+ per 5 X 10(5) daltons, no higher than that present in the unaggregated crystallins. No evidence was found for covalent bonding in the aggregate. Results of polyacrylamide gel electrophoresis and double immunodiffusion indicated the presence of alpha- and beta- but not gamma-crystallin in the HMW protein.(ABSTRACT TRUNCATED AT 250 WORDS)