Effect of hydrolysis products on the enzymatic degradation of polyethylene terephthalate nanoparticles by a polyester hydrolase from Thermobifida fusca

• Factors limiting the degradation of PET nanoparticles by polyester hydrolases were investigated.
• The intermediate hydrolysis products MHET and BHET were identified as competitive inhibitors of the PET hydrolase TfCut2.
• Product inhibition by MHET was identified as a limiting factor in the biocatalytic hydrolysis of PET.

The biocatalytic hydrolysis of post-consumer polyethylene terephthalate (PET) is a promising approach for an environmentally friendly plastic recycling process. The influence of intermediate hydrolysis products on the degradation of PET by TfCut2, a polyester hydrolase from Thermobifida fusca, was analyzed by reversed-phase HPLC. Nanoparticles prepared from PET films as substrate were hydrolyzed by the enzyme in the presence of ethylene glycol, terephthalic acid, bis(2-hydroxyethyl) terephthalate (BHET) and mono-(2-hydroxyethyl) terephthalate (MHET). The initial reaction rates were determined and kinetically analyzed using a model for PET degradation. BHET and MHET were identified as competitive inhibitors with similar binding constants. The reaction efficiency (Ef) for the hydrolysis of MHET was considerably lower compared to BHET indicating MHET as a relevant inhibitor of the enzymatic hydrolysis of PET nanoparticles by TfCut2. The results demonstrate the importance of product inhibition of the hydrolysis of PET by TfCut2 for the further improvement of biocatalytic plastic recycling processes.

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