Mushroom monophenol

Tyrosinase inhibitors prevent browning in foodbecause they inhibit the oxidation caused by the enzyme tyrosinase. Cuminaldehyde is identified as a potent mushroom tyrosinase monophenol monooxygenase inhibitor from cumin seeds, ft inhibits the oxidation of L-3,4-dihydroxyphenylalanine (l-DOPA) by mushroom tyrosinase with an ID50 of 7.7g/ml (0.05 mM). Its oxidized analogue, cumic acid (p-isopropylbenzoic acid), also inhibits this oxidation with an 1D50 of 43g/ml (0.26mM). These two inhibitors affect mushroom tyrosinase activity in different ways (Kubo and Kinst-Hori, 1998). 

Tyrosinase (see Copper Proteins with Dinuclear Active Sites), a copper metalloenzyme with a very broad phylogenetic distribution, is responsible for the browning of fruits and mushrooms.Tyrosinase is a bifimctional phenol oxidase that is able to both hydroxylate monophenols like tyrosine (monooxygenase reaction, (equations)) and snbseqnently oxidize the diphenol product to the corresponding quinone (oxidase reaction, (equation 6)) at a single Type 3 binuclear copper active site. 

Most PPO preparations from potato, apple, mushroom, and bean possess both monophenol and diphenol oxidase activities, whereas those from tea leaf, tobacco, mango, banana, pear, peach, and sweet cherry have been reported not to act on monohydroxyphenols [28]. Whether a single enzyme system exhibits both mono- and diphenol oxidase activities is still unclear. It was suggested that both cresolase and catecholase functions are catalyzed by a single site. Verdedoncella apple PPO showed both monophenol and diphenol oxidase activities with a reaction mechanism involving one... 

Catechol and pyrogallol are good substrates for the mushroom enzyme. In crude preparations monophenols are also oxidized, but with a lag period. As purification proceeds the ability to oxidize monophenols is lost. The ability to oxidize monophenols was named cresolase activity by the Nelson school, as p-cresol was used as a representative substrate. 

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