Section 6.4: Diffusion-Controlled Reactions

There is a theoretical upper limit to the rate of reactions in solution, based upon the diffusion coefficients of reactant molecules, which determines how often they collide with each other
Under physiological conditions, this limit is around 10⁸ to 10⁹ M^-1s^-1
A few kinds of enzymes approach this limit, and some, incredibly, even pass it
In order to accelerate a reaction to the diffusion limit, an enzyme must essentially catalyze a reaction between substrates for every collision that occurs
Under physiological conditions, the velocity is determined by the second-order rate constant k_cat/K_m, so enzymes that catalyze at the diffusion limit have rate constants near this value