Deep eutectic solvent tailoring the electrode-enzyme interface for phenylalanine dehydrogenase immobilization and...

Area of Science:

• Biocatalysis and enzyme immobilization
• Green chemistry and sustainable solvents
• Bioelectrosynthesis and electrochemical regeneration

Background:

• Deep eutectic solvents (DESs) offer tunable properties for enzyme immobilization.
• Hierarchical zeolitic imidazole framework-8 (HZIF-8) provides a robust support structure.
• Phenylalanine dehydrogenase is crucial for amino acid synthesis and cofactor regeneration.

Purpose of the Study:

• To investigate the efficacy of HZIF-8 and halogenated DESs for immobilizing phenylalanine dehydrogenase.
• To optimize enzyme activity and stability for L-homophenylalanine production.
• To develop a bioelectrosynthetic system for phenylpyruvate production using immobilized enzymes and electrochemical regeneration.

Main Methods:

• Immobilization of phenylalanine dehydrogenase onto HZIF-8 using three halogenated DESs (I, Cl, Br).
• Enzyme activity assays for L-homophenylalanine production from ethyl 2-oxo-4-phenylbutyrate (EOPB).
• Stability studies through multiple reaction cycles.
• Integration of immobilized enzyme onto a poly(methylene blue) electrode for electrochemical NAD+ regeneration.
• Bioelectrosynthesis of phenylpyruvate using phenylalanine-ethanolamine (Phe-MEA) or L-phenylalanine (L-Phe) as substrates.

Main Results:

• Optimal activity of 6.11 U/mg achieved at 70°C with a 5.4-fold increase compared to the free enzyme.
• 78.4% of original enzyme activity retained after six recycles.
• Successful bioelectrosynthesis of phenylpyruvate, yielding 13.85 mM using Phe-MEA.
• High total turnover numbers (TTN) for NADH regeneration: 138.5 (Phe-MEA) and 102.2 (L-Phe).

Conclusions:

• HZIF-8 combined with halogenated DESs is an effective system for phenylalanine dehydrogenase immobilization.
• The immobilized enzyme exhibits enhanced stability and activity, enabling efficient biocatalysis.
• The developed bioelectrosynthetic approach offers a sustainable method for phenylpyruvate production with efficient cofactor regeneration.