Diffusion-controlled reactions of enzymes. A comparison between Chou's model and Alberty-Hammes-Eigen's model

In the study of enzyme-catalysed mechanisms, it is often necessary to calculate the upper limit of enzyme reaction, which is usually used as an important criterion to identify whether an assumed enzyme-catalysed mechanism is reasonable or not. Basically, in the existing methods, there are two kinds of models, the Alberty-Hammes-Eigen model and the Chou model, for calculating the upper limit of enzyme reaction. In this paper, an analysis and comparison between these two models are made. It is pointed out that the magnitude of the van der Waals' binding energy between enzyme and substrate molecules will play a key role in deciding whether there is a significant difference or not for the results calculated from these two models. Through such a comparison, the role of the major protein outside the active site of an enzyme molecule also becomes obvious; if the van der Waals' binding energy is very small, the major protein will act like a 'wall', blocking the flow of some substrate molecules to the active site; while if the van der Waals' energy is greater than 3 kT (where k is the Boltzmann constant and T the absolute temperature), the major protein will behave like a 'accelerator', speeding up the flow of the substrate molecules to the active site around the enzyme molecule.