OXIDATION OF 6-HYDROXYDOPAMINE CATALYZED BY TYROSINASE

1. The oxidation of 3,4-dihydroxyphenylethylamine (dopamine) by O2 cat alyzed by tyrosinase yields 4-(2-aminoethyl)-1,2-benzoquinone, with it s amino group protonated (o-dopaminequinone-H+), which evolves non-enz ymatically through two branches or sequences of reactions, whose respe ctive operations are determined by the pH of the medium. 2. The cycliz ation branch of o-dopaminequinone-H+ takes place in the entire range o f pH and is the only significant branch at pH greater-than-or-equal-to 6.3. The hydroxylation branch of o-dopaminequinone-H+ only operates s ignificantly at pH < 6, and involves the accumulation of 2,4,5-trihydr oxyphenylethylamine (6-hydroxydopamine), identified by high performanc e liquid chromatography (HPLC). 4. 6-hydroxydopamine is also a substra te of tyrosinase. The identification and evolution of the oxidation pr oducts of 6-hydroxydopamine has been carried out by spectrophotometry and HPLC assays.