Oxidation of 6-hydroxydopamine catalyzed by tyrosinase.
1. The oxidation of 3,4-dihydroxyphenylethylamine (dopamine) by O2 catalyzed by tyrosinase yields 4-(2-aminoethyl)-1,2-benzoquinone, with its amino group protonated (o-dopaminequinone-H+), which evolves non-enzymatically through two branches or sequences of reactions, whose respective operations are determined by the pH of the medium. 2. The cyclization branch of o-dopaminequinone-H+ takes place in the entire range of pH and is the only significant branch at pH > or = 6. 3. The hydroxylation branch of o-dopaminequinone-H+ only operates significantly at pH < 6, and involves the accumulation of 2,4,5-trihydroxyphenylethylamine (6-hydroxydopamine), identified by high performance liquid chromatography (HPLC). 4. 6-hydroxydopamine is also a substrate of tyrosinase. The identification and evolution of the oxidation products of 6-hydroxydopamine has been carried out by spectrophotometry and HPLC assays.
Rodriguez-López
J N
JN
Departamento de Química-Física, Universidad de Castilla-La Mancha, Spain.
Varón
R
R
García-Cánovas
F
F
D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000031:analogs & derivatives / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006892:Hydroxydopamines; D007211:Indoles / Q000378:metabolism; D007700:Kinetics; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D016627:Oxidopamine / Q000378:metabolism*; D011809:Quinones; D013053:Spectrophotometry; D013237:Stereoisomerism
D006892:Hydroxydopamines; D007211:Indoles; D011809:Quinones; C083552:1,2(4)-topaminequinone; C083549:dopaminechrome; D016627:Oxidopamine; D014442:Monophenol Monooxygenase; D004298:Dopamine