Modification Of Fe₃O₄/SiO₂–Supported Laccase By Cu²⁺ And Its Enzymatic Properties

Laccase, a kind of polyphenol oxidases, is able to oxidize substrates by reducing molecular oxygen to water and shows fairly wide speci?city to substrates such as paradiphenols, polyphenols, aromatic amines, aminophenols, and chlorophenols, these properties make laccase has a great application value in many fields. Compared with free laccase, magnetic nanoparticle as support for laccase immobilization has the characteristics of fast separation, easy to recovery and can be recycled. So magnetic nanoparticle have been regarded as excellent carriers for laccase immobilization. In this paper we immobilize laccase on magnetic Fe3O4/SiO2 support with small diameteter of 30 nm or so, which has high stabilities compared to free laccase. Rapid decolorization of azo dyes by this immobilized laccase has been reported previously.In both free laccase or immobilized laccase in the preservation after a period of time, the activity would be decreased or even deactivated, so how to improve the activity of laccase and repeated use are of particularly importantce. Some studies found that free laccase modified by copper ion or carrier chelation by copper ion, will promote the activity of laccase, and present better storage stability in the meantime. Therefore, in this paper, based on the as-prepared Fe3O4/SiO2-supported laccase, modification of this immobilized laccase with lower laccase loading using copper ion has been studied in present paper and the accompanied enzymatic properties were also investigated.The results are listed below:(1) With the initial concentration of laccase increasing, the amount of laccase loading also increases, the laccase loading was 26 mg/g when 50 mg of Fe3O4/SiO2 and 0.2 mg/mL of laccase concentration was used.(2) Compare with 100 mM and 140 mM of Cu2+ modification, the relative activity of the immobilized laccase with lower laccase loading after 120 mM of Cu2+ modification increased by 54 %.(3) The relative activity of the immobilized laccase on the fifth day’s modification by 120 mM of Cu2+ was much better than the other days’, and correspondingly specific surface area was the highest, 28.073 m2/g.(4) The modified immobilized laccase has an optimum pH 5.0 and optimum temperature 40 ℃.(5) The modified immobilized laccase can be reused for the degradation of the procion dyes solution with a concentration of 10mg/L, even 13 cycles later, the decolorization percentage is still up to 92 %.(6) After storage for one month at room temperature, the modified immobilized laccase has better relative activity than that before modification, demonstrating a better storage stability.