Actin filament capping protein from bovine brain.

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Abstract
An actin filament capping protein was purified from bovine brain. The protein had a native MW of 63 kilodaltons (kd) with subunits of 36 kd and 31 kd and is globular in shape. It nucleates actin polymerization, inhibits filament elongation and filament interactions and decreases the steady state viscosity of F-actin in substoichiometric amounts (molar ratio 1:1000). The protein increases the critical concentration for actin polymerization. Neither Ca2+ nor calmodulin affects it action. All these effects can be explained by the binding of the protein to the barbed end of actin filaments leading to a blockade of actin monomer addition at the preferred growing end. This is directly demonstrated by EM. Concerning the polypeptide composition, Ca2+-independence, mode and stoichiometry of actin interaction, the protein is similar to the capping protein, previously isolated from Acanthamoeba.