Phoresis and Enhanced Diffusion Compete in Enzyme Chemotaxis

Area of Science:

• Biophysics
• Chemical Physics
• Biochemistry

Background:

• Enzyme chemotaxis, movement in response to substrate gradients, is experimentally observed but poorly understood.
• Existing theories do not fully account for the microscopic interactions between enzymes and substrates.

Purpose of the Study:

• Develop a microscopic theory for enzyme chemotaxis applicable to enzymes and small molecules.
• Investigate the contributions of nonspecific interactions and specific binding to enzyme movement.
• Clarify the relationship between enhanced diffusion and chemotaxis direction.

Main Methods:

• Formulated a microscopic theory incorporating nonspecific enzyme-substrate interactions.
• Included specific binding leading to complex formation.
• Analyzed the interplay between diffusiophoresis and binding-induced diffusion changes.

Main Results:

• Identified two key chemotaxis mechanisms: diffusiophoresis and binding-induced diffusion modification.
• Demonstrated that binding-induced diffusion can lead to movement towards or away from substrates.
• Showed that diffusiophoresis dominates at high substrate concentrations, while binding-induced diffusion dominates at low concentrations.
• Resolved experimental contradictions regarding urease chemotaxis direction.

Conclusions:

• The developed theory explains enzyme chemotaxis by considering both phoretic and binding effects.
• Enzyme movement direction depends on the balance between these two mechanisms and substrate concentration.
• This understanding allows for the engineering of nanomachines with controlled movement relative to substrate gradients.