Effect of AOT on enzymatic activity of the organic solvent resistant tyrosinase from Streptomyces sp. REN-21 in aqueous solutions and water-in-oil microemulsions

Abstract

The effect of AOT (sodium-bis(2-ethylhexyl sulfosuccinate)) on enzymatic activity of the organic solvent resistant tyrosinase (OSRT) in aqueous phosphate buffer solutions and in water-in-oil microemulsions of the water/AOT/isooctane system has been investigated. In contrast to mushroom tyrosinase, AOT does not activate OSRT in aqueous solutions, altering its activity very little at concentrations lower than 2 mM. Increasing contents of AOT in isooctane reduce the observed initial reaction rates of oxidation of t-butylcatechol (tBC) and 4-methylcatechol (4-MC). Similarly to mushroom tyrosinase, the effect has been described using an equation based on preferential binding of the substrates by surfactant interface layers. The apparent Michaelis–Menten substrate binding constants increase linearly with AOT concentration (with slopes of 0.12 ± 0.02 and 0.051 ± 0.006 for tBC and 4-MC, respectively), and the effective enzyme turnover number in the microemulsions remains practically constant.