TYROSINASE - MOLECULAR AND ACTIVE-SITE STRUCTURE

Tyrosinase, a widely distributed copper-containing monooxygenase, is a key enzyme in the biosynthesis of melanins and other polyphenolic compounds. It catalyzes both the hydroxylation of monophenols to o-diphenols (cresolase activity) and the oxidation of o-diphenols to o-quinones (catecholase activity). In many plants, the enzyme is responsible for the undesirable browning reaction, occurring particularly during the processing of fruits and vegetables. Tyrosinase has been isolated from a variety of sources, but pigment contamination and the occurrence of multiple forms have frequently hampered its characterization. Progress in the last decade has, however, allowed the construction of a rather detailed picture of the molecular structure and the reactivity of tyrosinase. In particular, the interaction of the unique binuclear copper complex in this enzyme with O-2, substrates and inhibitors is now well understood at the molecular level. Moreover, comparison of the cloned DNA sequences of tyrosinases from many different species (bacteria, fungi, plants and mammals) revealed two conserved histidine-rich regions, involved in the binding of the active site copper.