Tyrosinase insect

Burmester, T. and K. Scheller (1996). Common origin of arthropod tyrosinase, arthropod hemocyanin, insect hexamerin, and dipeteran arylphorin receptor. J. Mol. Evol. 42 713-728. 

Tyrosinase inhibition may be a potential approach to prevent and control the enzymatic browning reactions and improve the quality and nutritional value of food products [20]. Tyrosinase also plays a major key role in the developmental and defensive functions of insects. Tyrosinase is involved in melanogenesis, wound healing, parasite encapsulation, and sclerotization in insects [21-23]. For these reasons, in recent years the development of tyrosinase inhibitors has become an active alternative approach to control insect pests [20]. Additionally, it is now well-recognized that tyrosinase inhibitors are important for their potential applications in medical and cosmetic products [24-26]. 

Hemolymph JHE from Day 2 of the fifth instar larvae of T. ni was used (L3D2), diluted 1 500 with 0.08M phosphate buffer (pH-7.4 with 0.1% phenylthiourea to inhibit tyrosinases). The main reason for choosing this insect was that a great deal of effort has been put into the characterization of larval carboxylesterases and JHE in T. ni (39,40). In L3D2 larvae, the JHE titer is near its maximum (19). CIO 3H labeled JH III (New England Nuclear) and unlabeled JH III (Calbiochem) were used as substrate solubilized in abs.ethanol. 

The phenoloxidases are a related group of copper containing enzymes that catalyze the oxidation of phenols to quinones in animals and plants (5,6). Two distinct types of phenoloxidases that have substrate specificities and inhibitor sensitivities resembling typical tyrosinases and laccases are found in different types of insect cuticle (Z 8). Peroxidases, heme-containing enz)niies that also oxidize diphenols to quinones, may be present in cuticle and may play a role in sclerotization (9,10). 

Inhibition of insect laccases was first studied by Yamazaki found that this enzyme is inhibited by cyanide and diethyldithiocarbamate, but is fairly insensitive to thiourea and carbon monoxide. Studies by Andersen (8) and Barrett (23) have shown that laccases from many insect species are less sensitive to phenylthiourea, but more sensitive to azide than are tyrosinases. In our laboratory, we have also found that laccase from M. sexta is less sensitive to phenylthiourea than is tyrosinase, but carbon monoxide has not proven useful for distinguishing the two types of phenoloxidases (18). Laccase is reportedly inhibited by mono-... 

Interfering with tyrosinase, an enzyme of cuticle synthesis in insects (D 22.2.5)... 

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. 

Insect Protyrosinase and Tyrosinase. Tyrosinase has been isolated from grasshopper eggs as a protyrosinase by Allen and Bodine. This precursor already contains copper. Activation occurs when any of a large number of environmental conditions is changed, such as ionic strength, pH, or temperature. Surface-active agents (as aerosols) are effective activators. Cyanide can be used to remove metal from this enzyme also, and activity can be restored by the addition of copper. 

Tyrosinases are ubiquitous oxidative enzymes that use molecular oxygen to convert phenols into quinones. These quinones are reactive intermediates that undergo further reactions with various nucleophiles. In nature, tyrosinase-catalyzed reactions are responsible for the browning of food(16), the setting of mussel ghxe(5-I0) and the hardening of insect shells(77-79/... 

Phenolases (tyrosinases) are widely distributed in the plant kingdom (champignon mushrooms, potatoes, bananas). They are responsible for the darkening of freshly cut surfaces of plants or fruits. For insects, phenolases are important both for melanin formation and for browning and hardening (sclerotization) of the cuticle. 

The genus Curcuma includes some 30 species, native to India and the southeast of Asia. An extract is produced from the rhizomes, whose main components are curcumin and its derivatives. This extract has well-known anti-inflammatory, antioxidant, wound healing, anti-microbial and tyrosinase inhibitory properties. Its versatility makes it suitable for a number of cosmetic formulations on the basis of its anti-ageing, photo-protective, sensitive skin treatment, skin whitening, antiseptic and insect-repellent properties (Srimal, 1997). 

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