A multicomponent reaction-diffusion model of a heterogeneously distributed immobilized enzyme.

Area of Science:

• Biocatalysis
• Chemical Engineering
• Pharmaceutical Synthesis

Background:

• Industrial synthesis of antibiotics like cephalexin often utilizes immobilized enzymes for efficiency.
• Immobilized enzymes, such as penicillin G acylase (Assemblase), can exhibit different reaction kinetics compared to free enzymes.
• Suboptimal product yields and increased by-product formation are observed in some immobilized enzyme systems.

Purpose of the Study:

• To develop a physical model for cephalexin synthesis using immobilized penicillin G acylase (Assemblase).
• To elucidate the complex interplay of factors contributing to suboptimal conversion in immobilized enzyme systems.
• To provide insights for improved biocatalyst design and optimization of bioconversion processes.

Main Methods:

• Development of a physical model incorporating heterogeneous enzyme distribution, electrostatically coupled transport, and pH-dependent reactant dissociation.
• Validation of the model using experimental synthesis data across a range of substrate concentrations (50–600 mM), temperatures (273–303 K), and pH values (6–9).
• Analysis of intraparticle process dynamics, including predicted pH gradients within the biocatalytic particle.

Main Results:

• The model successfully predicted cephalexin synthesis under various diffusion limitations.
• Severe intraparticle pH gradients were predicted, consistent with previous experimental findings.
• The model demonstrated the significant impact of coupled transport and pH effects on overall conversion efficiency.

Conclusions:

• The developed physical model provides a comprehensive understanding of cephalexin synthesis with immobilized Assemblase.
• Insights into intraparticle pH gradients and their influence are crucial for optimizing biocatalyst performance.
• The modular nature of the model allows for its potential application to other enzymatic bioconversions.