Reaction Pathways for the Enzymatic Degradation of Poly(Ethylene Terephthalate): What Characterizes an Efficient PET-Hydrolase?

Bioprocessing of polyester waste has emerged as a promising tool in the quest for a cyclic plastic economy. One key step is the enzymatic breakdown of the polymer, and this entails a complicated pathway with substrates, intermediates, and products of variable size and solubility. We have elucidated this pathway for poly(ethylene terephthalate) (PET) and four enzymes. Specifically, we combined different kinetic measurements and a novel stochastic model and found that the ability to hydrolyze internal bonds in the polymer (endo-lytic activity) was a key parameter for overall enzyme performance. Endo-lytic activity promoted the release of soluble PET fragments with two or three aromatic rings, which, in turn, were broken down with remarkable efficiency (k(cat)/K-M values of about 10(5) M(-1)s(-1)) in the aqueous bulk. This meant that approximatly 70 % of the final, monoaromatic products were formed via soluble di- or tri-aromatic intermediates.

Automated summary

Bioprocessing of polyester waste is a promising approach for achieving a cyclic plastic economy. This study focuses on the enzymatic breakdown of poly(ethylene terephthalate) (PET) and reveals the crucial role of endo-lytic activity in overall enzyme performance. The release of soluble PET fragments with two or three aromatic rings through endo-lytic activity leads to efficient breakdown of the polymer in aqueous bulk, contributing to the formation of monoaromatic products.