Y-L-Glutaminyl-3,4-benzoquinone

The quinone imine (542) is formed in vitro and also presumably in the mushroom from y-L-glutaminyl-3,4-benzoquinone (543) according to the mechanism shown in Scheme 90 (489). y-L-Glutaminyl-3,4-benzoquinone (543) is itself produced by the action on y-L-glutaminyl-4-hydroxybenzene (544) of an enzyme with tyrosinase activity which has been purified from extracts of A. bisporus (109, 706, 707). y-L-Glutaminyl-4-hydroxybenzene (544) constitutes 1-2% of the dry matter of the gills of A. bisporus (635, 708) and is present also in the closely related A. hortensis (383). 

Glutamic acid and its derivatives have been found in several microorganisms. The common edible mushroom, Agaricus bisporus, contains y-L-glutaminyl-4-hydroxybenzene (3.46) which is formed from 4-aminophenol and glutamic acid. This metabolite is readily hydroxylated to y-L-glutaminyl-3,4-dihydroxybenzene and oxidized to the 3,4-benzoquinone. This ort/zo-quinone decomposes to an iminoquinone, 2-hydroxy-4-iminocyclohexa-2,5-dieneone (3.47), which imparts a red colour to some mushrooms. 

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