Abstract

Mono-oxygenase (also called cresolase) activity of mushroom tyrosinase (MT) can be optimized in the presence of 0.35 mM of sodium dodecyl sulfate (SDS). Spectrophotometric kinetic studies on MT revealed that the optimum temperature for the cresolase reaction was about 35°C both in the absence and presence of SDS. Circular dichroism studies of the thermal denaturation of MT between 20°C to 90°C disclosed that the secondary structure experienced minor changes in the presence of SDS, while changes in the tertiary structure were significant. The tertiary structure was destabilized by 15.7 kJ/mol in the presence of SDS. Differential scanning calorimetric studies on MT, in the absence and presence of SDS, produced two different profiles. The former showed an irreversible peak with Tm at 72°C and the latter showed a reversible peak with Tm about 37°C. Deconvulation analysis of the reversible peak was in good agreement with three transitions with Tm values of 33, 36 and 39°C, respectively. Considering the results of the kinetic studies, CD, and differential scanning calorimetry, it was concluded that the best performance of the cresolase activity of MT was achieved after a spatial change in the tertiary or quaternary structure caused by SDS. To reach this particular conformation, three structural transitions happen, which could be referred to the changes in the spatial positions of the domains or its subunits.