| Actin is one of the two major structural proteins found in muscle, in a large number of organisms. It is one of the most abundant eukaryotic proteins and plays a central role in cell motility, cytokinesis, phagocytosis, platelet clot retraction and other mechanochemical activities of the cell. Actin is synthesized as a monomeric globular protein G-actin, and these monomeric units aggregate through non-covalent forces (hydrophobic/hydrophilic interactions) giving rise to the filamentary polymeric form of F-actin.;Although this polymerization is interesting, the mechanism and driving force of this process has not yet been fully understood. In an entropically driven process, the G-actin molecules polymerize to F-actin under appropriate conditions of temperature, concentration of actin, and concentration of salts added. The functional characteristics of actins include their ability to self assemble into filaments of F-actin at physiological salt concentrations and the ability of these filaments to stimulate ATPase activity of myosin.;The main goal of this project was to obtain thermodynamic information on the polymerization of actin and use this to better analyze the process of polymerization. We present results on the extent of polymerization for actin as a function of temperature for appropriate concentrations of actin, salt, and for different solvent conditions, using labeled fluorescence. We observed an unanticipated new feature in which there occurred a decrease in the extent of polymerization after a maximum was reached. We also show that glass containers have an effect on actin polymerization.;Statistical mechanical theories have been developed to make predictions about polymerization. We have compared the theoretical values predicted by the mean field theory to the measured values of the extent of polymerization of actin and have shown that this model does not describe the polymerization of actin. We have also obtained kinetic information on the elongation rates of the actin polymerization process. |
