title: Switch between tyrosinase and catecholoxidase activity of scorpion hemocyanin by allosteric effectors.
abstract: Phenoloxidases and hemocyanins have similar type 3 copper centers although they perform different functions. Hemocyanins are oxygen carriers, while phenoloxidases (tyrosinase/catecholoxidase) catalyze the initial step in melanin synthesis. Tyrosinases catalyze two subsequent reactions, whereas catecholoxidases catalyze only the second one. Recent results indicate that hemocyanins can also function as phenoloxidases and here we show for the first time that hemocyanin can be converted to phenoloxidase. Furthermore, its substrate specificity can be switched between catecholoxidase and tyrosinase activity depending on effectors such as hydroxymethyl-aminomethan (Tris) and Mg(2+)-ions. This demonstrates that substrate specificity is not caused by a chemical modification of the active site.
authors.affiliation: Institut für Molekulare Biophysik der Johannes Gutenberg Universität Mainz, Jakob-Welder-Weg 26, Mainz, Germany.
authors.forename: Dorothea
authors.initials: D
authors.lastname: Nillius
authors.forename: Elmar
authors.initials: E
authors.lastname: Jaenicke
authors.forename: Heinz
authors.initials: H
authors.lastname: Decker
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D002384:Catalysis / Q000187:drug effects; D004156:Catechol Oxidase / Q000378:metabolism*; D004298:Dopamine / Q000737:chemistry / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D006433:Hemocyanins / Q000378:metabolism*; D006458:Hemolymph / Q000187:drug effects / Q000201:enzymology; D015636:Magnesium Chloride / Q000494:pharmacology; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D012605:Scorpions / Q000187:drug effects / Q000201:enzymology*; D013057:Spectrum Analysis; D013379:Substrate Specificity / Q000187:drug effects; D014439:Tyramine / Q000737:chemistry / Q000378:metabolism
chemical_list: D015636:Magnesium Chloride; D006433:Hemocyanins; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; D004298:Dopamine; D014439:Tyramine