Diffusion control in reversible enzyme reactions. Applications to carbonic anhydrase.

Area of Science:

• Biochemistry
• Physical Chemistry
• Enzyme Kinetics

Background:

• Enzymatic reactions are fundamental to biological processes.
• The rate of enzymatic reactions can be influenced by various factors, including substrate availability and product removal.
• Diffusional motion in the aqueous medium can impose physical limitations on reaction rates.

Purpose of the Study:

• To determine the theoretical upper limit for reversible enzymatic reaction rates imposed by diffusion.
• To investigate the roles of reactant diffusion to and product diffusion away from the enzyme.
• To evaluate proposed reaction mechanisms for carbonic anhydrase against these diffusion-limited rates.

Main Methods:

• Theoretical analysis of diffusion-limited reaction rates in bulk aqueous medium.
• Derivation of general equations for diffusion-controlled enzymatic reactions.
• Application of derived equations to specific reaction schemes of carbonic anhydrase.

Main Results:

• Diffusion of both reactants to the enzyme and products away from the enzyme can be rate-limiting.
• An upper limit to the possible reaction rate was established based solely on diffusion.
• A reaction scheme for carbonic anhydrase involving HCO3- as a substrate and direct buffer-enzyme interaction is consistent with diffusion limits.

Conclusions:

• Diffusional transport is a critical determinant of maximal enzymatic reaction velocity.
• The proposed mechanism for carbonic anhydrase aligns with physical constraints imposed by diffusion.
• Other potential reaction pathways for carbonic anhydrase were excluded based on diffusion limitations.