Tiron as a substrate for mushroom tyrosinase

Abstract

Tiron (4,5-dihydroxy-1,3-benzene disulphonic acid) can serve as a substrate for mushroom tyrosinase with a K m value of 34 mM. The product(s) formed is yellow (λ max 435 nm) and is stable with time. An intermediate product, having significant absorbance at 3685 nm (probably tiron- o-quinone), was detected and the kinetics of its conversion to the final yellow product(s) was studied. Hydrogen peroxide (at 0.03–1.3 mM) accelerated the conversion of the intermediate compound to the yellow product(s). Tiron-semiquinone was detected by EPR spectroscopy during the initial phase of Tiron oxidation by mushroom tyrosinase. Maximum EPR signal intensity due to Tiron-semiquinone and the time required to reach maximum intensity were dependent on the amount of mushroom tyrosinase but not on the presence or absence of hydrogen peroxide (3.3 mM). In view of separate studies showing that the yellow product(s) is mainly a low M, polymerized Tiron-quinone, suggestions as to possible pathways by which such a product(s) is formed are discussed.