Tyrosinase/catecholoxidase activity of hemocyanins: structural basis and molecular mechanism.
The enzymes tyrosinase, catecholoxidase and hemocyanin all share similar active sites, although their physiological functions differ. Hemocyanins serve as oxygen carrier proteins, and tyrosinases and catecholoxidases (commonly referred to as phenoloxidases in arthropods) catalyze the hydroxylation of monophenols or the oxidation of o-diphenols to o-quinones, or both. Tyrosinases are activated in vivo by limited proteolytic cleavage, which might open up substrate access to the catalytic site. It has recently been demonstrated that if hemocyanins are subjected to similar proteolytic treatments (in vitro) they also exhibit at least catecholoxidase reactivity. On the basis of their molecular structures, hemocyanins are used as model systems to understand the substrate-active-site interaction between catecholoxidases and tyrosinases.
Decker
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H
Institut für Molekulare Biophysik, Johannes Gutenberg Universität Mainz, D-55099 Mainz, Germany. decker@biophysik.biologie.unimainz.de
Tuczek
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F
D000818:Animals; D001665:Binding Sites / Q000502:physiology; D004156:Catechol Oxidase / Q000737:chemistry* / Q000378:metabolism; D004789:Enzyme Activation; D006433:Hemocyanins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D015394:Molecular Structure; D014442:Monophenol Monooxygenase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D013379:Substrate Specificity
D006433:Hemocyanins; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase