Oxidation of 3,4-dihydroxymandelic acid catalyzed by tyrosinase.
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.
Martínez Ortiz
F
F
Departamento de Química-Física, Facultad de Ciencias Químicas, Universidad de Murcia, Spain.
Tudela Serrano
J
J
Rodríguez López
J N
JN
Varón Castellanos
R
R
Lozano Teruel
J A
JA
García-Cánovas
F
F
D001487:Basidiomycota / Q000201:enzymology; D004156:Catechol Oxidase / Q000378:metabolism*; D008333:Mandelic Acids / Q000378:metabolism*; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010504:Periodic Acid; D011048:Polarography; D013057:Spectrum Analysis
D008333:Mandelic Acids; D010504:Periodic Acid; C000989:3,4-dihydroxymandelic acid; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase