Potential of acetylacetone as a mediator for Trametes versicolor laccase in enzymatic transformation of organic pollutants

Abstract

Low-cost and environmentally friendly mediators could facilitate the application of laccase (EC 1.10.3.2) in variant biotechnological processes. Acetylacetone (AA) represents an inexpensive and low toxic small molecular diketone that has been proven as an effective mediator for laccase in free radical polymerization. However, the potential of AA as a mediator for laccase in pollutant detoxification and/or degradation is still unknown. In this work, the roles of AA in laccase-induced polymerization and transformation were investigated. AA was demonstrated to be a highly efficient mediator in the laccase-induced grafting copolymerization of acrylamide and chitosan. The efficacy of AA in the laccase-induced decoloration of malachite green (MG) was compared with that of the widely used 1-hydroxybenzotriazole (HBT). The laccase-AA system had the highest turnover number (TON, 39.1 μmol/U), followed by the laccase-only system (28.5 μmol/U), while the TON of the laccase-HBT system was the lowest (14.9 μmol/U). The pseudo-first-order transformation rate constant (k 1) of MG in the laccase-AA system was up to 0.283 h(-1) under the given conditions, while the k 1 of AA caused by laccase was only 0.008 h(-1). In the five-cycle run, the concentration of AA remained stable. The larger TON of the laccase-AA system and the stability of AA in the cycling runs demonstrate that AA was more recyclable than HBT in the LMS, leading to a prolonged serving life of laccase. These results suggest that AA might be a potential redox mediator for laccase.

A High Redox Potential Laccase from Pycnoporus sanguineus RP15: Potential Application for Dye Decolorization

“…Furthermore, the E ° of a laccase restrains the substrates that it may oxidize to those with lower E °. This limitation may be overcome by using redox mediators, which increase the oxidative capacity of the enzyme towards the oxidation of higher E ° compounds; however, the industrial use of mediators is still hampered by their prohibitive cost and toxicity [ 4 , 7 , 8 , 9 ]. Therefore, high-redox potential laccases are more attractive for biotechnological purposes.…”

“…Synthetic dyes often have low biodegradability, several are toxic, carcinogenic and mutagenic and it is not uncommon that their degradation products show similar properties. Furthermore, the absorption and reflection of the sunlight by dyes in surface waters interferes with bacterial and plant growth, disturbing the ecological balance [ 9 , 11 , 12 ]. As a result, there is a great interest in the development of efficient treatments for the removal of synthetic dyes from wastewaters.…”

“…Furthermore, numerous synthetic dyes are resistant to microbiological attack. Thus, the use of oxidative enzymes is now considered the most promising alternative for the removal of dyes from industrial effluents [ 9 , 10 , 11 , 13 , 14 ]. The large-scale use of laccases for wastewater treatments is, however, severely limited by their high production costs.…”

Radical-Mediated Enzymatic Polymerizations

“…Laccases, copper-containing oxidoreductases that are obtained from a variety of organisms, commonly fungi, including Pycnoporus coccineus [ 58 ], Myceliophthora thermophile [ 59 ], Trametes trogii [ 60 ], and Trametes versicolor [ 61 , 62 , 63 ], catalyze the reduction of molecular oxygen while concurrently oxidizing a hydrogen-donating substrate (see Figure 6 ) [ 59 ]. These reactions result in the formation of radical-bearing species and have been utilized in pulp/paper [ 64 ], food/beverage, and waste treatment applications [ 65 , 66 ].…”

“…In an exploration of the pollutant removal ability of a laccase-bearing polymer matrix, Zhang and coworkers first grafted poly(acrylamide) to chitosan in a laccase-mediated polymerization [ 62 ]; once again, the necessity of a mediator, acetylacetone, was confirmed as no polymer formed in its absence. The resulting combination of the chitosan-poly(acrylamide) graft copolymer, laccase, and acetylacetone were then successfully used to decolorize a model organic pollutant, malachite green, confirming that laccase was not deactivated during the formation of the chitosan-poly(acrylamide) graft copolymer.…”