V. Kahn et al., p-hydroxyphenylpropionic acid (PHPPA) and 3,4-dihydroxyphenylpropionic acid (3,4-DPPA) as substrates for mushroom tyrosinase, J FOOD BIOC, 23(1), 1999, pp. 75-94
p-Hydroxyphenylpropionic acid (PHPPA) and 3,4-dihydroxyphenylpropionic acid
(3,4-DPPA) serve as substrates for tyrosinase. The Km value of 3,4-DPPA fo
r tyrosinase is 1.3 mM. The yellow o-quinone of 3,4-DPPA. (4-carboxyethyl-o
-benzoquinone) (lambda(max) = 400nm), is detected initially and it is then
converted to a red product(s) (lambda(max) = 480+/-10 nm), the o-quinone of
6,7-dihydroxy 3-dihydrocumarin (dihydroesculetin). When the concentration
of the latter is relatively high, it polymerizes to a final brown product(s
), characterized by an ill-defined spectrum.
H2O2 shortens the lag period of PHPPA hydroxylation, hastens the conversion
of the yellow o-quinone of 3,4-DPPA to the red o-quinone of dihydroesculet
in, and prevents the polymerization of the latter to the final brown produc
t(s).
The relatively unstable o-quinone of 3, 4-DPPA interacts with amines such a
s hydroxylamine (NH2OH), p-aminosalicylic acid (PASA) and p-aminobenzoic ac
id (PABA), forming relatively stable final product(s) characterized by diff
erent spectra from those formed in their absence.
Acetohydroxamic acid (AHA) and salicylhydroxamic acid (SHAM) each has an ef
fect on the spectrum of product(s) obtained when 3, 4-DPPA is oxidized by t
yrosinase, indicating that these hydroxamic acids derivatives interact with
the o-quinone of 3, 4-DPPA. The spectrum of the final product(s) was also
different when 3,4-DPPA was oxidized by tyrosinase in the presence of benze
nesulfinic acid than in its absence, suggesting the formation of a stable p
henylsulfonyl derivative.