Bioenergetic aspects and polymer length distribution in steady-state head-to-tail polymerization of actin or microtubules.

Wegner's theory of steady-state head-to-tail polymerization of actin (or microtubules) is extended somewhat in order to show the explicit role of the ATP (or GTP) free energy of hydrolysis (X) in the steady-state kinetics. The monomer flux and the ATP flux can both be expressed in terms of X and rate constants of the model. Both fluxes approach zero as X leads to 0 (by variation of the concentrations of ATP, ADP, and Pi); this limit corresponds to ATP equilibrium. The dependence of rate constants on these concentrations is examined. Free energy levels of the monomer kinetic cycle and the rate of free energy dissipation are discussed. The steady-state polymer length distribution is derived for a special case.