| We investigate the effects of the nonequilibrium process of nucleotide hydrolysis upon the dynamics of actin polymerization via a combination of analytic theory, computer stochastic simulation and numerical integration. Specifically, we show that experimentally observed polymerization dynamics are not artifacts of the fluorescence assays, but rather are genuine features that must result when nucleotide hydrolysis within actin molecules is considered. Additionally, we offer the first model of pyrene fluorescence that accurately describes previously discordant experimental polymerization data. We also investigate the effect of branching and serving stimuli upon actin polymerization. We show that branching and severing stimuli have different characteristic dynamics and how these effects depend upon the concentration of capping protein in solution and the rate of nucleotide exchange. Finally, we offer a new method of calculating polymerization time courses---which accounts for the intrinsically nonequilibrium dynamics of actin polymerization during hydrolysis---that will be useful to both specialists and non-specialists alike. |
