Mechanistic aspects of the control of tyrosinase activity

There is now much evidence suggesting that there are multiple control points in the process of melanin production. The most fundamental process of melanogenesis is centered on the oxidative activity of the enzyme tyrosinase. Tyrosinase is a highly unusual enzyme in that it apparently catalyses two processes, i.e., the oxidation of tyrosine and the dehydrogenation of dihydroxyphenylalanine (Dopa), at the same active site. The reactions involved account for the unusual kinetics of tyrosine oxidation and suggest biochemical mechanisms whereby the activity of the enzyme and the process of melanogenesis may be modified. It is proposed that the oxidative engine of melanogenesis resides in an oxidation/reduction cycle involving Dopa and dopaquinone and that this can be modified by processes that result in the removal of dopaquinone or Dopa from the reaction system.