title: Immobilization of laccase by encapsulation in a sol-gel matrix and its characterization and use for the removal of estrogens.
abstract: Laccase from Myceliophthora thermophila was immobilized by encapsulation in a sol-gel matrix based on methyltrimethoxysilane and tetramethoxysilane. The amount of laccase used for the preparation of the hydrogel was in the range 2.2-22 mg of protein/mL sol and the corresponding enzymatic activities were in the range 5.5-17.0 U/g biocatalyst. The kinetic parameters of the encapsulated laccase showed that the immobilized enzyme presented lower affinity for the substrate 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS). However, the stability of laccase was significantly enhanced after immobilization; thus, both pH and thermal stability improved about 10-30% and tolerance to different inactivating agents (NaN(3) , ZnCl(2) , CoCl(2) , CaCl(2) , methanol, and acetone) was 20-40% higher. The reusability of the immobilized laccase was demonstrated in the oxidation of ABTS for several consecutive cycles, preserving 80% of the initial laccase activity after 10 cycles. The feasibility of the immobilized biocatalyst was tested for the continuous elimination of Acid Green 27 dye as a model compound in a packed-bed reactor (PBR). Removals of 70, 58, 57, and 55% were achieved after four consecutive cycles with limited adsorption on the support: only 10-15%. Finally, both batch stirred tank reactor (BSTR) operated in several cycles and PBR, containing the solid biocatalyst were applied for the treatment of a solution containing the endocrine disrupting chemicals (EDCs): estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2). Eliminations of EDCs in the BSTR were higher than 85% and the reusability of the biocatalyst for the degradation of those estrogens was demonstrated. In the continuous operation of the PBR, E1 was degraded by 55% and E2 and EE2 were removed up to 75 and 60%, at steady-state conditions. In addition, a 63% decrease in estrogenic activity was detected.
authors.affiliation: Dept. of Chemical Engineering, School of Engineering, University of Santiago de Compostela, Santiago de Compostela, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Lloret
authors.forename: G
authors.initials: G
authors.lastname: Eibes
authors.forename: G
authors.initials: G
authors.lastname: Feijoo
authors.forename: M T
authors.initials: MT
authors.lastname: Moreira
authors.forename: J M
authors.initials: JM
authors.lastname: Lema
authors.forename: F
authors.initials: F
authors.lastname: Hollmann
mesh_terms: D055162:Biocatalysis; D052244:Endocrine Disruptors / Q000378:metabolism*; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000737:chemistry*; D004967:Estrogens / Q000378:metabolism*; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D042845:Laccase / Q000737:chemistry* / Q000378:metabolism; D020037:Sordariales / Q000201:enzymology*
chemical_list: D052244:Endocrine Disruptors; D004800:Enzymes, Immobilized; D004967:Estrogens; D005656:Fungal Proteins; D042845:Laccase