Activation of mammalian tyrosinase by ferrous ions

Mammalian tyrosinase from B16 mouse melanoma is significantly activated by Fe2+. Monitoring of tyrosine oxidn. by both dopachrome formation and O2 consumption showed that Fe2+ at micromolar concns. induce a marked enzymic activity with 0.01 U/mL of highly purified tyrosinase, whereas no detectable reaction occurs in the absence of metal over a sufficiently prolonged period of time. The extent of the activating effect, which is specific for the reduced form of Fe, is proportional to the concn. of the added metal with a typical satn. profile, no further effect being obsd. beyond a threshold value. Changing the buffer system from phosphate to Hepes or Tris results in a marked decrease of the Fe2+-induced activation. Scavengers of active O species, such as superoxide dismutase, catalase, formate, and mannitol have no detectable effect on the tyrosinase. These results are accounted for in terms of an activation mechanism involving redn. of the Cu2+ at the active site of the resting enzyme.