High terephthalic acid purity: Effective polyethylene terephthalate degradation process based on pH regulation with dual-function hydrolase

Eco-friendly enzymatic-recycling has been widely utilized in tackling plastic pollution. However, the limited activity on the polyethylene terephthalate (PET) degradation product mono-hydroxyethyl terephthalate (MHET) leads to the formation of heterogeneous hydrolysis products, resulting in PET downcycling. Herein, by applying a dual-function PET hydrolase Is PETase PA with balanced PET and MHET degradation efficiency, an effective PET hydrolysis process was developed to enhance the terephthalic acid (TPA) product purity. Firstly, the impact of pH on the catalytic activity of Is PETase PA revealed that the pH reduction caused by TPA generation hindered the complete conversion of MHET to TPA. Further investigation of the catalytic mechanism showed that the pH-induced protonation of H208 in the catalytic triad destabilized the interaction between Is PETase PA and MHET. Thus, by introducing pH regulation strategy on the bifunctional Is PETase PA , the single-enzyme process could achieve high-purity TPA recovery (>99 %). Overall, this work ensured the high-quality PET enzymatic-recycling for effectively addressing plastic pollution.