Dithiothreitol inactivation of frog epidermis tyrosinase

Frog epidermis tyrosinase inactivation by dithiothreitol (DTT), both in the proenzyme and active forms, have been studied. Upon increasing DTT:enzyme-up to 1o(6):1 ratios and depending on the incubation period, two inactivation steps both in proenzyme and enzyme were observed. Enzyme lost its activity faster than proenzyme. Oxygen favoured inactivation. After dialysis of the DTT:protein (10(6):1) incubation medium, 20% of the original enzyme activity was recovered. However it decreased to 15% if the enzyme had been incubated with substrate. Conformational changes due to loss of activity were not shown on the fluorescence spectra.