Repurposing Commercial Hydrolytic and Oxidative Enzymes toward Synergistic PLA Depolymerization

The enzymatic depolymerization of polylactic acid (PLA) under mild conditions remains a major challenge in sustainable plastic recycling. Here, we report a synergistic system combining Tritirachium album proteinase K (PrK) with two commercial biocatalysts, Candida rugosa lipase (Lip) and Glycine max lipoxygenase (LOX I-B), that enhances PLA degradation far beyond individual enzyme performance. PrK alone hydrolyzed amorphous solvent-cast PLA (VPLA) and postconsumer PLA (PCPLA) with moderate efficiency, but the addition of Lip led to a 5.7-fold increase in lactic acid (LA) release on VPLA and a 2.7-fold increase on PCPLA, achieving similar to 60% conversion within 72 h. Similarly, LOX I-B, while catalytically inactive on its own, boosted PrK-mediated VPLA hydrolysis up to 2.5-fold, dependent on molecular oxygen, and yielded pyruvate as a trace oxidative product. Mechanistic investigations revealed that both Lip and LOX I-B promote PrK binding to PLA surfaces, enhancing productive interactions with the polymer. Additionally, Lip hydrolyzed soluble oligo-lactide (O-LA) intermediates generated by PrK, contributing to monomer release. High-resolution mass spectrometry and FTIR spectroscopy confirmed substrate-dependent synergy, surface modifications, and the progressive removal of O-LA species. The study demonstrates that enzymatic cocatalysis using trace amounts of auxiliary hydrolases or redox enzymes can significantly accelerate PLA depolymerization. These findings establish a mechanistic framework for multienzyme systems in polyester biodegradation and offer a promising biocatalytic strategy for scalable PLA recycling.