Tyrosinase source

Evidence tom a variety of sources indicates that the active site of tyrosinase is very similar to that of hemocyanin, a dioxygen-binding protein found in molluscs and arthropods (15,16). This type of active site contains two copper ions, which are cuprous in the deoxy state, and which reversibly bind dioxygen, forming the oxy form of the enzyme or protein in which a peroxy ligand bridges between two cupric ions. 

The dominant feature of tyrosinase is that it has both cresolase and catecholase activity. Laccase has a very clear catecholase activity, but its cresolase activity is not so clear. Mason, Fowlks, and Peterson (109) used 02 to label 3,4-dimethylphenol during the tyrosinase-catalyzed oxidation of this compound and showed that the source of the oxygen introduced into the phenol in the phenolase reaction was molecular oxygen according to Reaction 1. 

Biosensors based on a Clark oxygen electrode, coupled to tyrosinase immobilized by three different methods, were investigated for the determination of phenol in real matrices, such as water of various natural sources, industrial wastes and oil press. The feasibility study included direct use of the biosensors and in situ analysis. An integrated system, incorporating SPE, desorption, fractionation and biosensor detection, was validated for screening phenolic compounds in water. Two types of electrode were tested, solid graphite and CPE incorporating tyrosinase. Correct analyses were found for river water samples spiked with phenol (10 p.gL ), p-cresol (25 p.gL ) and catechol (1 A mul-... 

A crnde extract of sweet potato Ipomoea-batatas (L.) Lam.) was nsed as a source of phenol oxidases (polyphenoloxidase, tyrosinase, catecholoxidase, EC 1.14.18.1). The extract was directly placed in the carrier of a FIA system with UVD, to promote oxidation of phenolic compounds to o-quinones that condense to form melanin-like pigments with a strong absorption at 410 nm. The determination of phenols in industrial wastewaters showed good agreement with conventional methods (correlation coefficient 0.9954) LOD was 10 p,M, with RSD <2.7% (w = 6). Under optimal storage conditions the enzymatic activity did not vary for at least five months . 

Park YD et al. (2006) TXM13 human melanoma cells a novel source for the inhibition kinetics of human tyrosinase and for screening whitening agents. Biochem Cell Biol 84(1) 112-116... 

The crystal structures of tyrosinase from Streptomyces castaneoghbisporus HUT 6202 and catechol oxidase from the sweet potato Ipomoea batata have been determined. They confirm that the coordination of the type-3 copper site in tyrosinase and catechol oxidase is very similar to that found in hemocyanin. This had been deduced before from the similarity of spectroscopic properties and a comparison of many tyrosinase and hemocyanin primary structures. On the basis of the biological source of the proteins seven different domain organizations could be identified. Plant catechol oxidases of different organisms have a sequence identity of about 40-60%. The sequence identity between catechol oxidases and mulluscan hemocyanins is about 35% over almost the whole length of the sequences. In contrast, the sequence identity between plant catechol oxidases and other type-3 copper proteins from any nonplant source is limited to the two copperbinding regions. 

The traditional view of enzymatic melanogenesis, expressed by different authors (SS, 145, 242), holds that tyrosinase is the melanogenic enzyme, and studies on in vitro melanogenesis using mushroom tyrosinase have been considered as valid for mammalian melanogenesis as well, although the enzymes isolated from different sources show qualitative differences (27, 126). 

In an alternative approach to mimic tyrosinase activity a copper(I)-copper(n) redox couple and a hydroquinone-quinone redox couple were incorporated in one complex (scheme 17). The hydroquinone moiety should act as an electron shunt between an external reducing agent, i.e. ascorbic acid, zinc or electrochemical reduction, and the copper ions. Catalytic oxygenation by monooxygenases is usually accompanied by the formation of water, with the aid of an external electron and proton source.35 46 Activation of O2 by dinuclear copper(I) complex 58 results in superoxo- or p-peroxo-dicopper(II) complex 59, which oxygenates an external substrate molecule. Internal electron transfer to quinone dicopper(II) complex 60 is followed by quinone to hydroquinone reduction. The electron transfer system shown here is reminiscent of the quinone based systems found in the primary photochemical step of bacterial photosynthesis, and in (metallo)porph3nin-quinone electron transfer systems.In contrast to expectation, the hydroquinone dinuclear copper(II) complex 60 (L = (2-pyridylethyl)formidoyl, scheme 17), designed to mimic step c in this cycle, is a stable system in which the hydroquinone moiety is not oxidized to a quinone structure 61. 

Tyrosinases from various sources also catalyze the hydroxylation of phenols to catechols and the oxidation of catechols to o-quinones [139]. 

Anionic dyes can be removed from textile effluent streams at acidic pH with chitosan through protonated amine complexation with anionic dye sites. Phenols are common waste products in paper processing. Application of mushroom enzyme tyrosinase to the stream specifically converts phenols into quinones, which can subsequently be absorbed by chitosan. Toxic polychlorinated hiphenols (PCBs), commonly used in plastic processing and lubricants, are a significant source of water contamination. Although the nature of the interaction is not currently known, chitosan treatment shows potential in lowering PCB concentrations. 

Oxidations now known to be catalyzed by copper-containing enzymes were noticed over a century ago, when Schoenbein observed that oxidation of natural substrates resulted in pigment formation in mushrooms. Individual enzymes were gradually identified laccase by Yoshida in 1883 and tyrosinase by Bertrand in 1896. However, it was not imtil potato polyphenol oxidase was isolated in 1937 by Kubowitz that the role of copper was defined. The family of copper oxidases includes a number of enzymes of both plant and animal origin that may very probably be found to react through similar mechanisms, but which exhibit a number of individual characteristics. The enzymes to be described in this section include potato phenol oxidase, mushroom polyphenol oxidase (tyrosinase), laccase, mammalian and insect tyrosinase, and ascorbic acid oxidase. Each of these differs in certain respects from the others, and undoubtedly other related enzymes will be described from other sources that resemble these, but also display individualities. In these cases, identities in nomenclature must not be extended to imply identities in enzyme structure or activity. 

The oxidation of tyrosine to 3,4-dihydroxyphenylalanine (DOPA) is a well-established reaction that occurs enzymatically under the influence of tyrosinase. The presence of tyrosinase has been shown in mammalian tissues, a particularly good source being the Harding-Passey mouse melanoma. " Lemer et determined that the enzymatic activity for tyrosine and DOPA is associated with cytoplasmic particles and that the two activities are not separable. Preparations can be obtained which have a long induction period before the onset of the oxidation of tyrosine and... 

The results of LaDu and Zannoni on dog liver enzyme were substantiated by Hager c< al. 212) on enzyme preparations from beef and pig liver The enzyme from these sources were purified by ethanol precipitation, (NH4)2S04 precipitation, and chloroform-ethanol treatment. A purification of about a hundredfold was achieved. These authors suggest that p-hydroxyphenylpyruvate oxidase is a copper enzyme with properties similar to tyrosinase. Additional support for this is the relative insensitivity of the enzyme to CO and CN and the very high affinity for O2. 

Mushroom tyrosinase is popular among researchers as it is commercially available and inexpensive. It plays a critical role in tyrosinase inhibitor studies for its use in cosmetics as well as in food industries, and many researches have been conducted with this enzyme, which is well studied and easily purified from the mushroom A an cMS bisporus. No matter in terms of inhibitory strength, inhibitory mechanism, chemical structures, or the sources of the inhibitors, the search for new inhibitors based on mushroom tyrosinase has been so successful that various different types of inhibitors have been found in the past 20 years (Chang, 2009 Parvez, 2007 Seo, 2003). 

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