Improving biocatalytic microenvironment with biocompatible ε-poly-L-lysine for one step gluconic acid production in low pH enzymatic systems

Surface amine modification could not only improve the microenvironment near the active sites of enzyme, but also enhance the multi-point chemical crosslinking between the enzyme and carrier. The linear structured polymer of ε-poly-L-lysine (EPL) is an ideal donor of amino with much more exposed on the surface for enzyme attachment. Analysis of the result of dynamic light scattering (DLS) and circular dichroism (CD) demonstrated the favorable electrostatic interactions and negligible impact on the conformation of enzymes, Glucose Oxidase and Catalase (GOx&CAT). Titration and dissociation curve together with Zeta-potential characterization revealed that enzymes (EPL@GOx&CAT) under the protection of EPL had more stable structure and better activity and stability in acidic reaction environment. Meanwhile, the activity recovery of immobilized EPL@GOx&CAT increased to 1.56 times higher than that of GOx&CAT, and the acid resistance was improved by 1.44 times with the optimum pH shifting to acidic by 0.50 unit. The substrate affinity was raised with the decrease of K_m from 5.98 to 4.35 mg mL⁻¹. Thus, the gluconic acid production in low pH system could be increased by pH-engineering of the enzyme microenvironment via conjugation with positively charged polyelectrolyte.