NATURAL F-ACTIN .3. NATURAL F-ACTIN AS INACTIVE POLYMER

1. 1. Natural F-actin was found to be short in length, and the length distribution was not changed by storage demonstrating that an end-to-end interaction between natural F-actins was lacking. 2. 2. Natural F-actin never accelerated the G-F transformation of Straub G-actin, but a great acceleration was produced by sonic treatment. 3. 3. Depolymerization, sonic ATPase and the exchange of bound divalent cations of natural F-actin occurred more slowly than with Straub F-actin demonstrating that natural F-actin was more stable than Straub F-actin. 4. 4. The effect of β-actinin, tropomyosin and myosin on Straub F-actin was examined, but all the characteristics of natural F-action could not be explained by their presence. 5. 5. To explain the behavior of natural F-actin, it was postulated that some additional factors other than the blocking by β-actinin of the ends of natural F-actin existed. © 1969.