Studies of the chemo-mechanical conversion in artificially produced streamings. III. Dynamic cooperativity--a new cooperativity in actomyosin systems with a polarized arrangement of F-actin.

The order--disorder phase transition in the chemo-mechanical process in our streaming system, which was reported in the preceding paper [Yano, M. & Shimizu, H., J. Biochem, 84, 1087--1092], was studied in detail. Starting from the hypothesis that a new type of cooperativity, dynamic cooperativity, is present in the elementary cycles of the chemo-mechanical conversion, quantitative and consistent agreement was obtained between the theoretical and experimental data on the temperature dependences of the streaming velocity and the ATPase activity, including the presence of the phase transition. The hypothesis was also supported by observations of the temperature dependence of the ATPase activity in resisted streaming. The physical and physiological significance of dynamic cooperativity is considered. It is shown that dynamic cooperativity arises in actomyosin system which have a polarized arrangement of F-actin by directed streaming of the solution, because the rate of the elementary cycle can be accelerated by the streaming. Furthermore, dynamic cooperativity is the key mechanism of self-organization of a dynamical order such that in ordered motions, and is one of the essential conditions for the direct conversion of the chemical energy of ATP to the mechanical energy of ordered and directed motion.