Enzymatic degradation of poly-[(R)-3-hydroxybutyrate]: Mechanism, kinetics, consequences

Abstract

Poly-[(R)-3-hydroxybutyrate] (PHB) films prepared by compression molding and solvent casting, respectively, were degraded with the intracellular depolymerase enzyme natively synthetized by the strain Bacillus megaterium. Quantitative analysis proved that practically only (R)-3-hydroxybutyric acid (3-HBA) forms in the enzyme catalyzed reaction, the amount of other metabolites or side products is negligible. The purity of the product was verified by several methods (UV-VIS spectroscopy, liquid chromatography, mass spectroscopy). Degradation was followed as a function of time to determine the rate of enzymatic degradation. Based on the Michaelis-Menten equation a completely new kinetic model has been derived which takes into consideration the heterogeneous nature of the enzymatic reaction. Degradation proceeds in two steps, the adsorption of the enzyme onto the surface of the PHB film and the subsequent degradation reaction. The rate of both steps depend on the preparation method of the samples, degradation proceed almost twice as fast in compression molded films than in solvent cast samples. The model can describe and predict the formation of the reaction product as a function of time. The approach can be used even for the commercial production of 3-HBA, the chemical synthesis of which is complicated and expensive.

Unraveling the Interplay between Abiotic Hydrolytic Degradation and Crystallization of Bacterial Polyesters Comprising Short and Medium Side-Chain-Length Polyhydroxyalkanoates

“…Abiotic hydrolysis of PHB and PHOHHx (co)­polyesters under physiological-like pH (PBS, pH = 7.4) is expected to be an extremely slow process. Moreover, it was previously found that hydrolytic and enzymatically catalyzed degradation of PHA by extracellular e-PHA depolymerase enzymes occurs at alkaline pH. − With the aim of conducting abiotic degradation experiments at elevated pH, the influence of pH on the chain conformation and the crystallization behavior of the polymer was studied.…”

Beyond Intracellular Accumulation of Polyhydroxyalkanoates: Chiral Hydroxyalkanoic Acids and Polymer Secretion

“…PHB degradation studies by extracellular depolymerases are typically performed using PHB films as substrate, producing R3HBA as the hydrolysis product (Polyák et al, 2018), thus limiting the access of enzymes to its substrate. In order to achieve high R3HBA titers, a high initial concentration of PHB should be used.…”

Synthesis of Poly(Hexamethylene Succinate-Co-Ethylene Succinate) Copolymers With Different Physical Properties and Enzymatic Hydrolyzability by Regulating the Ratio of Monomer

“…One promising class of degradable polymers is aliphatic polyesters which are biocompatible, biodegradable, and thermally stable. As such, copolyesters have attracted growing attention and are used in a wide range of applications, including biomedical materials, disposable packaging, and agricultural films ( Pan et al, 2018 ; Polyák et al, 2018 ; Siracusa and Blanco, 2020 ; Kesavan et al, 2021 ).…”