title: Characterization of phenoloxidase activity in Sydney rock oysters (Saccostrea glomerata).
abstract: Phenoloxidase (PO) activity was studied in Sydney rock oysters (Saccostrea glomerata). As in other molluscs, PO was found to exist as a pro-enzyme (proPO) in hemocytes. ProPO could be activated to PO by exogenous proteases (trypsin and chymotrypsin), exposure of hemocytes to pathogen-associated molecular patterns (PAMPs) and by the detergents, Triton X-100 and sodium dodecyl sulphate (SDS). Inhibition studies confirmed the proPO activating system of Sydney rock oysters is a proteinase cascade in which Ca2+ dependent serine proteinases proteolytically convert proPO into active PO. Activated PO was found to be a tyrosinase-like enzyme that is responsible for both monophenolase and diphenolase activity. The bifunctional PO had higher affinity for the monophenol, hydroquinine monomethyl ether (4HA) (Km=4.45+/-1.46 mM) than for the diphenol, l-DOPA (Km=10.27+/-1.33 mM). Maximum enzyme activity was evident at 37 degrees C, pH 8 and at salinities of between 30 and 37 ppt. Melanogenesis catalysed by the active enzyme is a composite of eumelanin and the product of a sclerotin pathway combining DOPA decarboxylase with PO activity.
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, NSW, 2109, Australia.
authors.forename: Saleem
authors.initials: S
authors.lastname: Aladaileh
authors.forename: Peters
authors.initials: P
authors.lastname: Rodney
authors.forename: Sham V
authors.initials: SV
authors.lastname: Nair
authors.forename: David A
authors.initials: DA
authors.lastname: Raftos
mesh_terms: D000818:Animals; D003902:Detergents / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D004792:Enzyme Precursors / Q000378:metabolism; D006434:Hemocytes / Q000201:enzymology; D006458:Hemolymph / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D019746:Intramolecular Oxidoreductases / Q000378:metabolism; D007700:Kinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors / Q000097:blood / Q000378:metabolism*; D010125:Ostreidae / Q000201:enzymology*; D011480:Protease Inhibitors / Q000494:pharmacology; D011802:Quinidine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D054712:Salinity; D012697:Serine Endopeptidases / Q000378:metabolism; D013696:Temperature; D015054:Zymosan / Q000378:metabolism / Q000494:pharmacology
chemical_list: D003902:Detergents; D004792:Enzyme Precursors; D008070:Lipopolysaccharides; D011480:Protease Inhibitors; C014486:hydroquinidine; D015054:Zymosan; D014442:Monophenol Monooxygenase; D012697:Serine Endopeptidases; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase; D011802:Quinidine