Catalytic activity of Cerrena unicolor laccase in aqueous solutions of water-miscible organic solvents—Experimental and numerical description

The stability and catalytic activity during oxidation of syringaldazine (SGZ) by laccase from Cerrena unicolor (CUL) was studied in aqueous solutions of ethanol, acetone and dimethyl sulfoxide (DMSO). Additional, the oxidation of other two substrates, catechol (CAT) and 2,6-dimethoxyphenol (DMOP), was studied in ethanol and in DMSO solutions, respectively. It was observed that in 3 M solutions of the studied solvents CUL was practically stable for 30 min of the experiments, which show its good applicability in solutions of water-miscible organic solvents. Moreover, it was observed that the effect of the tested organic solvents on the maximum rate of oxidation values (Vmax) of different substrates was not dependent on the substrate. Within the studied range of concentrations (up to 8 M) ethanol did not affect Vmax values and the presence of DMSO reduced it at roughly the same rate for the studied substrates. In the case of SGZ as a substrate, the effect of the solvent on Vmax values increased in the order ethanol < acetone < DMSO and in the case of KM in the order DMSO < acetone < ethanol. The experimental relationships between the content of organic solvents and the observed kinetic parameters were numerically described using the exponential relationships on the solvent concentrations, in the first approximations replacing the variability of the activity coefficients of the reactants. The fitted exponential coefficients were observed with the values observed for other fungal laccases and discussed.