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Oxidation of 3,4-dihydroxymandelic acid catalyzed by tyrosinase.

Biochimica et biophysica acta (1988-11-02)
F Martínez Ortiz, J Tudela Serrano, J N Rodríguez López, R Varón Castellanos, J A Lozano Teruel, F García-Cánovas
ABSTRACT

Tyrosinase usually catalyzes the conversion of monophenols to o-diphenols and the oxidation of o-diphenols to the corresponding quinones. However, when 3,4-dihydroxymandelic acid was provided as the substrate, 3,4-dihydroxybenzaldehyde was produced. These results led to the proposal that tyrosinase catalyzes an unusual oxidative decarboxylation of this substrate (Sugumaran, M. (1986) Biochemistry 25, 4489-4492). However, 3,4-dihydroxybenzaldehyde is also obtained through the oxidation of 3,4-dihydroxymandelic acid by sodium periodate and on a mercury electrode. These results led to the proposal that tyrosinase catalyzes the oxidation of the substrate into o-quinone, which reacts immediately with a molecule of substrate, oxidizing it and through decarboxylation generates an intermediate (quinone methide) which transforms into 3,4-dihydroxybenzaldehyde; simultaneously, the original o-quinone is reduced to 3,4-dihydroxymandelic acid.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
DL-3,4-Dihydroxymandelic acid, 95%