IDENTIFICATION OF PRODUCTS AND INTERMEDIATES DURING L-DOPA OXIDATION TO DOPACHROME USING HIGH-PRESSURE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

Products and intermediates produced during L-dopa oxidation by sodium periodate and mushroom tyrosinase were studied using high pressure liquid chromatography with electrochemical detection (HPLC-ED). The oxidation products and intermediates, including dopaquinone, leukodopachrome, 2,4,5-trihydroxyphenylalanine and its quinone species, were readily separated on a reverse-phase column with 15 mM citrate buffer, pH 3.0, containing 35 mM NaCl, 0.25 mM octyl sulfate and 0.7 mM Na2EDTA and detected at either a reductive (-100 mV) or an oxidative potential (750 mV) of the working electrode. Using these techniques, the effect of base and acid on the chemical reaction of dopaquinone to dopachrome was demonstrated.