Tyrosinase plant

Jimenez-Atienzar M, Escribano J, Cabanes J, Gandia-Herrero F and Garcia-Carmona F. 2005. Oxidation of the flavonoid eriodictyol by tyrosinase. Plant Physiol Biochem 43(9) 866-873. 

Gandia-Herrero, R, Escribano, J., and Garci a-Carmona, R, Betaxanthins as substrates for tyrosinase an approach to the role of tyrosinase in the biosynthetic pathway of betalains. Plant Physiol, 138, 421, 2005. 

Steiner, U., Schhemann, W., and Strack, D., Assay for tyrosine hydroxylation activity of tyrosinase from betalain-forming plants and cell cultures, Anal. Biochem., 238, 72, 1996. 

More recently (2006) we performed and reported quantitative structure-activity relationship (QSAR) modeling of the same compounds based on their atomic linear indices, for finding fimctions that discriminate between the tyrosinase inhibitor compounds and inactive ones [50]. Discriminant models have been applied and globally good classifications of 93.51 and 92.46% were observed for nonstochastic and stochastic hnear indices best models, respectively, in the training set. The external prediction sets had accuracies of 91.67 and 89.44% [50]. In addition to this, these fitted models have also been employed in the screening of new cycloartane compounds isolated from herbal plants. Good behavior was observed between the theoretical and experimental results. These results provide a tool that can be used in the identification of new tyrosinase inhibitor compounds [50]. 

Some non-silica sol-gel materials have also been developed to immobilize bioactive molecules for the construction of biosensors and to synthesize new catalysts for the functional devices. Liu et al. [33] proved that alumina sol-gel was a suitable matrix to improve the immobilization of tyrosinase for detection of trace phenols. Titania is another kind of non-silica material easily obtained from the sol-gel process [34, 35], Luckarift et al. [36] introduced a new method for enzyme immobilization in a bio-mimetic silica support. In this biosilicification process precipitation was catalyzed by the R5 peptide, the repeat unit of the silaffin, which was identified from the diatom Cylindrotheca fusiformis. During the enzyme immobilization in biosilicification the reaction mixture consisted of silicic acid (hydrolyzed tetramethyl orthosilicate) and R5 peptide and enzyme. In the process of precipitation the reaction enzyme was entrapped and nm-sized biosilica-immobilized spheres were formed. Carturan et al. [11] developed a biosil method for the encapsulation of plant and animal cells. 

Soler-Rivas C, Moller AC, Arpin N, Olivier JM and Wichers HJ. 2000. Induction of tyrosinase mRNA in Agaricus bisporus upon treatment with a tolaasin preparation from Pseudomonas tolaasii. Physiol Mol Plant Pathol 58 95-99. 

Polyphenol oxidase occurs within certain mammalian tissues as well as both lower (46,47) and higher (48-55) plants. In mammalian systems, the enzyme as tyrosinase (56) plays a significant role in melanin synthesis. The PPO complex of higher plants consists of a cresolase, a cate-cholase and a laccase. These copper metalloproteins catalyze the one and two electron oxidations of phenols to quinones at the expense of 02. Polyphenol oxidase also occurs in certain fungi where it is involved in the metabolism of certain tree-synthesized phenolic compounds that have been implicated in disease resistance, wound healing, and anti-nutrative modification of plant proteins to discourage herbivory (53,55). This protocol presents the Triton X-114-mediated solubilization of Vida faba chloroplast polyphenol oxidase as performed by Hutcheson and Buchanan (57). 

Since the oxidative polymerization of phenols is the industrial process used to produce poly(phenyleneoxide)s (Scheme 4), the application of polymer catalysts may well be of interest. Furthermore, enzymic, oxidative polymerization of phenols is an important pathway in biosynthesis. For example, black pigment of animal kingdom "melanin" is the polymeric product of 2,6-dihydroxyindole which is the oxidative product of tyrosine, catalyzed by copper enzyme "tyrosinase". In plants "lignin" is the natural polymer of phenols, such as coniferyl alcohol 2 and sinapyl alcohol 3. Tyrosinase contains four Cu ions in cataly-tically active site which are considered to act cooperatively. These Cu ions are presumed to be surrounded by the non-polar apoprotein, and their reactivities in substitution and redox reactions are controlled by the environmental protein. 

Tyrosinase. This enzyme is found in numerous organisms ranging tom bacteria and fungi to plants and animals. The best characterized tyrosinases are those tom mushrooms and tom N. crassa (11-14). The reactions catalyzed by tyrosinase are the hydroxylation of phenols to give catechols and the subsequent oxi tion of catechols to give o-quinones. 

Tyrosinase Various tyrosinase catalyse the formation of pigments (melanins) in a host of plants and animals. 

Tyrosinase inhibition. Methanol (80%) extract of the dried entire plant at a concentration of 100 (Xg/mL produced weak activity " " . 

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). 

This enzyme exhibits no hydroxylase activity and is involved in the final synthesis of many naturally occurring /t-quinoncs. e.g. the naphthaquinone juglone in walnut (1.58) and the benzoquinone arbutin (hydroquinone-(3-D-glucopyranoside 2.46). Arbutin is a plant cryo-protectant that stabilizes membranes (Hincha et al., 1999). This compound has medicinal properties and has, for example, been used to treat urinary tract infections in humans. It is also used to lighten skin color, because it inhibits tyrosinase and hence the formation of melanin. The derivative deoxyarbutin (2.47 note the difference in the sugar molecule) was recently reported to be considerably more effective as a skin-lightening compound (Boissy et al., 2005). 

Catechol melanin, a black pigment of plants, is a polymeric product formed by the oxidative polymerization of catechol. The formation route of catechol melanin (Eq. 5) is described as follows [33-37] At first, 3-(3, 4 -dihydroxyphe-nyl)-L-alanine (DOPA) is derived from tyrosine. It is oxidized to dopaquinone and forms dopachrome. 5,6-Dihydroxyindole is formed, accompanied by the elimination of C02. The oxidative coupling polymerization produces a melanin polymer whose primary structure contains 4,7-conjugated indole units, which exist as a three-dimensional irregular polymer similar to lignin. Multistep oxidation reactions and coupling reactions in the formation of catechol melanin are catalyzed by a copper enzyme such as tyrosinase. Tyrosinase is an oxidase con-... 

Further analysis of the UV spectrum revealed that this compound is a gallic acid derivative. A search of the Dictionary of Natural Products for molecular ion and plant genus name leads to the identification of a known compound - Pterocaryanin B. The compounds with poly-hydroxyl groups in their structures are very well known as tyrosinase inhibitors and are responsible for the inhibition of melanin synthesis. Therefore, no further isolation was necessary. 

Tyrosinase catalyzes the oxidation of phenols. These enzymes are widespread in fungi, plants, and animals. Polyhydroxystyrene (PHS) is a phenol-containing polymer used as the excellent polymer matrix due to its good coating properties. Phenol moieties of PHS can be oxidized by tyrosinase. Mushroom tyrosinase was observed to catalyze the oxidation of 1-2% phenolic moieties of the synthetic polymer poly (4-hydroxystyrene) (PHS) (Shao et al., 1999) (Figure 4.5). 

Li et al. (1990) developed an assay to measure the diphenol oxidase activity of tyrosine by following the conversion of 3,4-dihydroxymandelic acid (DHMA) to 3,4-dihydroxybenzaldehyde (DHBZ). Tyrosinase is involved in the formation of melanotic pigments in a wide variety of plants and animals. 

Evolution of two phenoloxidases, an arthropod and molluscan type. A close relationship between phenoloxidase and hemocyantn was deduced based on their similar sequences, physico-chemical properties and similar functions. But sequence comparisons also revealed that there is not a common phenoloxidase type the enzymes found in animals, plants, and fungi are different with respect to their sequences, size, glycosylation, and activation. Two different types of tyrosinases can be distinguished based on their sequences, structure, and function. One type (m-phenoloxidase) is more related to molluscan hemocyanin with respect to the active site. The other type (a-phenoloxidase), which is very similar to arthropod hemocyanins, is found in arthropods together with hemocyanins (Figure 9). ... 

The distinguishing feature of tyrosinase is that it catalyzes the oxidation of monohydric phenols, like tyrosine, to the dihydric form and dihydric phenols, like DOPA and catechol, to the corresponding quinones. The striking biological effects of this enzyme arise from quinones which polymerize to produce the darkening of various plants on injury and melanin in mammals. The relative oxidation rates of several dihydric phenols by tyrosinase are given in Table III. 

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