Characterization of phenoloxidase activity in Sydney rock oysters (Saccostrea glomerata)

Saleem Aladaileh, Rodney Peters, Sham V. Nair, David A. Raftos*

*Corresponding author for this work

Research output: Contribution to journalArticle

44 Citations (Scopus)

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 °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.

Original languageEnglish
Pages (from-to)470-480
Number of pages11
JournalComparative Biochemistry and Physiology - Part B: Biochemistry and Molecular Biology
Volume148
Issue number4
DOIs
Publication statusPublished - Dec 2007

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