Reaction kinetics in intracellular environments: The two proposed models yield qualitatively different predictions

A recently proposed model by Schnell and Turner for reaction kinetics in environments crowded by macromolecules is applied to elementary bimolecular binding. It is found that it leads to an unusual equilibrium constant equal to zero. The progress curves are qualitatively different from the prediction of a model based on a non-integer (fractal) power law proposed earlier by Savageau. In the case of the Michaelis-Menten reaction, the two models predict qualitatively similar progress curves and identical equilibrium concentrations. The two models are investigated analytically and numerically, and their differences are discussed in regard to possible validation of the models by use of experimental data.