Biocatalytic formation of synthetic melanin: The role of vanadium haloperoxidases, L-DOPA and iodide

The vanadium haloperoxidase (V-HPO) enzyme, extracted from the brown alga Laminaria saccharina, is able to catalyze the formation of a black precipitate, using as precursor the amino acid L-dopa in the presence of hydrogen peroxide and iodide, in one-pot synthesis. The L-dopa oxidation is a multistep reaction with a crucial role played by the iodide in the enzyme catalyzed peroxidative production of dopachrome, a well known intermediate in the synthesis of melanin. Dopachrome is then converted to a synthetic form of melanin through a polymerization reaction. Factors, such as buffer composition and pH, influence significantly the reaction first steps, but further steps of melanin production …