Study of prophenoloxidase activating system of freshwater crayfish (Pontastacus leptodactylus)

Phenoloxidase (Po) activity was measusred spectrophotometrically in serum, plasma and haemocytes (HLS) of the freshwater crayfish (Pontastacus leptodactylus). The highest activity was found in HLS suggesting that the haemocytes are the major source of the Po or its proform prophenoloxidase (proPO) in crayfish. Furthermore, the enzyme activity in serum samples was reduced after freezing the samples for 20 days at -20˚C. Po activity was cation-dependent and the peak of enzyme activity obtained using 5mM of CaCl2 or MgCl2 .Also, the Po activity in the HLS samples treated with different elicitors of 10% sodium dodecyl sulphate (10%SDS), b 1-3-glucan, Aeromonas hydrophila lipopolysaccharids (LPS) and trypsin resulted in variable activities with the highest and the lowest activities measured in samples treated with trypsin and 10% SDS, respectively. The marked enhancement induced by trypsin suggests the role of an endogenous proteinase which is probably able to promote the enzyme activity. To confirm the role of the proteinase on the proPO activating system, trypsin activity was also measured in the crayfish HLS.