Purification and characterization of calmodulin-dependent functional protein, phosphodiesterase, in the lens

Abstract

Calmodulin and calmodulin-dependent functional protein play an important role in the maintenance of lens transparency and homeostasis. In the present study, phosphodiesterase, one of the typical calmodulin-dependent functional proteins, was purified from bovine lens by DEAE-cellulose chromatography, calmodulin-Sepharose 4B chromatography and Superose 12 chromatography. Moreover, calmodulin-dependent phosphodiesterase, and independent phosphodiesterase were separated from crude lens extract using DEAE-cellulose column. The calmodulin-dependent phosphodiesterase was purified 4500-fold with a 0.7% yield; it was a dimer formed with two single polypeptides of 59K as the molecular weight. The enzyme had a higher affinity for cyclic GMP than for cyclic AMP, and functioned at calcium ion concentration above 10(-6) M in the incubation mixture. W-7 as calmodulin antagonist indirectly inhibited the enzyme activity and nifedipine as calmodulin-dependent phosphodiesterase antagonist directly inhibited the enzyme activity. These results suggest that an appearance of calmodulin-dependent phosphodiesterase activity depends on the interrelation between the calcium ion and calmodulin in the lens.