On the Oxidation Product of Catechol When Oxidized by Means of Tyrosinase

It was only natural that the earlier investigators of the action of the oxidase, tyrosinase, on catechol should have assumed that the first stage in the reaction is the formation of o-quinone. More recently this view of the reaction has gained additional approval from the studies carried on by Pugh and Raper (1). One of the difficulties encountered in trying to determine the nature of the initial oxidation product of the catechol is due to the great instability of o-quinone, especially when the latter occurs in an aqueous solution. Since o-quinone forms with aniline an insoluble dianilinoquinone, Pugh and Raper allowed the enzymatic oxidation of catechol to take place in the presence of aniline. The formation of the dianilinoquinone thus obtained is regarded by them as evidence that o-quinone is the initial oxidation product in the reaction. About 2 years previous to Pugh and Raper’s publication, Robinson and McCance (2) showed that in the oxidation of catechol by means of tyrosinase, 2 atoms of oxygen are used up per mole of catechol. Since only 1 atom of oxygen is required in converting catechol into o-quinone, the question naturally arises as to what becomes of this second atom of oxygen. Onslow and Robinson (3) have suggested that the oxidation of the catechol to o-quinone is accompanied by the formation of hydrogen peroxide.