Chicken‐Gizzard Actin: Polymerization and Stability

Preparations of chicken gizzard actin obtained from acetone‐dried muscle powders prepared with various methods developed for skeletal muscle contain variable amounts of a β‐actinin‐like protein. This contamination is minimized if the procedure of muscle powder preparation includes washing with EDTA solution, and can be completely removed by gel filtration of G‐actin on Sephadex G‐100. The presence of β‐actinin activity manifests itself in an increased rate of actin polymerization, low filament lengths resulting in low reduced viscosity and enhanced ATP‐splitting activity of actin polymer, and instability of the polymer in the absence of free ATP. Gizzard actin purified on a Sephadex G‐100 column does not differ from rabbit skeletal muscle actin in its polymerization properties. The distinct property of gizzard actin is the instability of its G form in the absence of added Ca²⁺, indicating that the affinity of this cation for the single high‐affinity site in gizzard actin is lower than in skeletal muscle actin.