Purification and characterization of prophenoloxidase from kuruma prawn Penaeus japonicus

A prophenoloxidase (proPO) was purified from hemocyte of kuruma prawn Penaeus japonicus. An 134-fold purification of the enzyme with 25% yield was achieved by a combination of several chromatographies. The molecular mass of the native proPO was estimated to be 330 kDa by gel filtration. In SDS-PAGE analysis, two closely migrating subunits of 78 kDa and 72 kDa were detected under a reducing condition. ProPO was activated by SDS and methanol. Phenoloxidase (PO), the active form of proPO, had its optimum pH and temperature at approximately 9 and 37 degrees C, respectively. The activity of PO depended on the concentrations of divalent cations, such as Mg2+ and Ca2+: the highest activity was obtained at the concentration of 50 mM for both ions. PO oxidized mono phenols and o-diphenol derivatives, but it was unable to oxidize the p-diphenol derivatives, suggesting PO from the prawn hemocyte catalyzes a consecutive reaction, hydroxylation of monophenols and deprotonation of o-diphenols.