Properties and kinetic behavior of free and immobilized laccase from Oudemansiella canarii: Emphasis on the effects of NaCl and Na₂SO₄ on catalytic activities

Studies have highlighted the great potential of Oudemansiella canarii laccase in degrading synthetic dyes for reducing their toxicity. Immobilization of enzymes improves usability in degradation processes and the present work succeeded in immobilizing this laccase onto MANAE-agarose. Immobilization improved pH, thermal, and storage stabilities. Both, free and immobilized enzymes presented Michaelis-Menten kinetics with the substrate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with K_m values of 0.056 ± 0.003 and 0.195 ± 0.022 mM, respectively. Immobilization increased V_max 1.27-fold. NaCl caused incomplete (hyperbolic) inhibition, which was satisfactorily described by the one-substrate one-modifier mechanism. Immobilization reduced the maximal inhibition by NaCl from 80.2 to 55.7 %. The effect of Na₂SO₄ was predominantly stimulation, but inhibition of the free enzyme occurred at high substrate concentrations. Stimulation of the immobilized enzyme by Na₂SO₄ was much more pronounced. It strongly depended on the substrate concentration and was much stronger (up to 300 %) at low substrate concentrations. The combined effects of substrate and sulfate on the immobilized laccase could be satisfactorily described by the one-substrate one-modifier mechanism. The modified response of the immobilized O. canarii laccase to NaCl and Na₂SO₄ considerably favors its use as a tool in bioremediation processes because environmental contamination by salts frequently represents a strong operational challenge.