Purification and characterization of a prophenoloxidase activating enzyme from crayfish blood cells

A proteinase was purified from crayfish haemocytes by affinity chromatography on heparin-sepharose and phenyl-sepharose, followed by DEAE-cellulose ion-exchange chromatography. This proteinase could mediate the conversion of prophenoloxidase (proPO) to its active form, phenoloxidase (PO), and its was therefore designated a prophenoloxidase activating enzyme, ppA.The purified ppA had a molecular mass of about 36,000 Da. Since ppA was a proteinase able to cleave chromogenic peptide substrates of trypsin, and serine proteinase inhibitors were strongly inhibitory towards ppA activity, the enzyme appeared to be a serine type proteinase. It exhibited maximal enzyme activity at neutral and slightly alkaline pH, and was sensitive to heat inactivation at 58°C.