KAHN, V., Department of Food Science, Agricultural Research Organization, Volcani Center, P. O. Box 6, Bet Dagan, Israel

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). Copyright © 1990, Wiley Blackwell. All rights reserved