2,3,4-TRIHYDROXYACETOPHENONE (2,3,4-THAP) AS A SUBSTRATE FOR MUSHROOM TYROSINASE

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2,3,4-Trihydroxyacetophenone (2,3,4-THAP) can serve as a substrate for mushroom tyrosinase with a Km value of 1.2 mM. The product(s) formed is yellow, characterized by a peak at 420–430 nm. A lag period in 2,3,4-THAP oxidation to the yellow product(s) in the presence of ascorbate indicates that the initial product(s) is an o-quinone of 2,3,4-THAP. An oxime, characterized by a broad peak at 510–650 nm, is the likely product formed between o-quinone of 2,3,4-THAP and NH2OH. The ɛm of the o-quinone of 2,3,4-THAP was estimated to be 1.6 × 104 M−1 cm−1 at 425 nm. During relatively long incubation periods, the peak of the yellow product(s) shifts from 420–425 nm to 430–440 nm; the solution remains yellow and transparent for at least a week and no precipitate is formed. The final yellow product(s) is probably a low molecular weight polymer of THAP-o-quinone (dimer, tetramer, etc).