title: A new bilirubin-degrading enzyme from orange peels.
abstract: A novel enzyme activity that catalyzes the degradation of unconjugated bilirubin (Bu) has been demonstrated in extracts of the peels of edible oranges. Unlike the few known bilirubin-oxidizing enzymes, the orange enzyme does not produce biliverdin as a product, does not seem to require oxygen, and has a unique absorption spectrum of its products. Even at the crude stage, the enzyme has a specific activity that is 10 and 20 times higher, respectively, than those reported for the crude or partially purified Bu-degrading enzymes from mushrooms and rat liver. The enzyme has a pH optimum near 7.5 and a Km value of 50-100 microM for Bu. The enzyme is remarkably stable, retaining over 50% activity after prolonged digestion with proteinase K or heating at 100 degrees C. Similar treatments inactivated the bilirubin oxidase from Myrothecium verrucaria MT-1. The enzyme is poorly soluble in water but can be partially solubilized with cholic acid, with a doubling in specific activity.
authors.affiliation: Department of Clinical Biochemistry, Toronto General Hospital, Ont., Canada.
authors.forename: T W
authors.initials: TW
authors.lastname: Wu
authors.forename: G S
authors.initials: GS
authors.lastname: Li
mesh_terms: D001663:Bilirubin / Q000378:metabolism*; D002957:Citrus; D004795:Enzyme Stability; D004798:Enzymes / Q000302:isolation & purification*; D006863:Hydrogen-Ion Concentration
chemical_list: D004798:Enzymes; D001663:Bilirubin