Monophenol monooxygenase

These copper ion-dependent enzymes [EC 1.10.3.1] (also referred to as diphenol oxidases, O-diphenolase, phe-nolases, polyphenol oxidases, or tyrosinases) catalyze the reaction of two catechol molecules with dioxygen to produce two 1,2-benzoquinone and two water. A variety of substituted catechols can act as substrates. Many of the enzymes listed under this classification also catalyze a monophenol monooxygenase activity [/.c., EC 1.14.18.1]. See also Monophenol Monooxygenase Tyrosine Monooxygenase... 

MONOPHENOL MONOOXYGENASE NITRITE REDUCTASE PHOTOSYSTEM I QUERCETIN 2,3-DIOXYGENASE SUPEROXIDE DISMUTASES COPROPORPHYRINOGEN OXIDASE... 

ACTIN REGULATORY PROTEINS MONOMOLECULARITY Monomolecular surface coverage, BIOMINERALIZATION MONOPHENOL MONOOXYGENASE... 

MONOPHENOL MONOOXYGENASE NITRIC OXIDE SYNTHASE PEPTIDYL GLYCINE a-AMIDATING MONOOXYGENASE... 

Polyphenol oxidase (PPO) (EC 1.14.18.1 monophenol monooxygenase [tyrosinase] or EC 1.10.3.2 0-diphenol 02-oxidoreductase) is one of the more important enzymes involved in the formation of black tea polyphenols. The enzyme is a metallo-protein thought to contain a binudear copper active site. The substance PPO is an oligomeric particulate protein thought to be bound to the plant membranes. The bound form of the enzyme is latent and activation is likely to be dependent upon solubilization of the protein (35). PPO is distributed throughout the plant (35) and is localized within in the mitochondria (36), the cholorplasts (37), and the peroxisomes (38). Using antibody techniques, polyphenol oxidase activity has also been localized in the epidermis palisade cells (39). Reviews on the subject of PPO are available (40—42). 

An alternative mechanism for the oxidation of phenolic compounds is enzyme-catalyzed oxidation. Several classes of enzymes can catalyze this reaction. According to the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology (NC-IUBMB), these enzymes are part of the E C. 1 class of oxidoreductases (see the Internet web site http //www.chem.qmul.ac.uk/iubmb/enzyme/ECl). The three main classes of enzymes that catalyze the oxidation of phenolic compounds are the oxidoreductases that use oxygen as electron acceptor (E.C. 1.10.3), the peroxidases (E.C. 1.11.1), and monophenol monooxygenase (E.C. 

This class includes enzymes that use diphenols or related compounds as electron donors and oxygen as the acceptor, thereby forming the oxidized donor and water. Members include catechol oxidase (E.C. 1.10.3.1), laccase (E.C. 1.10.3.2), and o-aminophenol oxidase (E.C. 1.10.3.4). Laccase is also known as / -diphenoloxidase. whereas catechol oxidase is also known as diphenoloxidase, phenoloxidase, polyphenoloxidase, o-diphenolase, phenolase and tyrosinase. Many of these names are also used in reference to a different enzyme, monophenol monooxygenase (E.C. 1.14.18.1). This enzyme will be discussed further in Section 1.8.2.2. 

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). 

Phenoloxidase (monophenol monooxygenase, E.C. 1.14.18.1) introduces one atom of molecular oxygen into the substrate and was used in alginate-entrapped cells or in partially purified form. The pharmaceutical 7,8-dihydroxy-N-(di-n-propyl)-2-aminotetralin was produced continuously using a phenol oxidase suspension in dialysis tubing in an airlift fermenter coupled to an aluminium oxide column for selective product isolation (Figure 16.3-13)[6S1. A product concentration of 130 mg/L and a yield of 25 % were reached. 

Oxygenases. They catalyze substrate oxidation by molecular oxygen with a hydrogen donor that may be the substrate itself. Example monophenol monooxygenase (EC 1.14.18.1)... 

Monophenol monooxygenase, loccase (EC 1.14.18.1) see Oxygen metabolism. Lignin. 

Tyrosinase (E.C. 1.14.18.1, monophenol monooxygenase) is a copper monooxygenases enzyme that catalyzes two different oxygen-dependent reactions, namely the oxidations of both monophenols (cresolase or monophenolase activity) and o-diphenols (catecholase or diphenolase activity) into reactive o-quinones [28, 89]. 

Polyphenol oxidase catalyzes two reactions first the hydroxylation of a monophenol to o-diphenol (EC 1.14.18.1, monophenol monooxygenase) followed by an oxidation to o-quinone (EC 1.10.3.1, o-diphenol oxygen oxidoreductase). Both activities are also known as cresolase and catecholase activity. At its active site, polyphenol oxidase contains two Cu ions with two histidine residues each in the ligand field. In an ordered mechanism (cf. 2.5.1.2.1) the enzyme first binds oxygen and later monophenol with participation of the intermediates shown in Fig. 2.8. The Cu ions change their valency (Cu Cu ). The newly formed complex ([] in Fig. 2.8) has a strongly polarized... 

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