Purification and characterization of prophenoloxidase from the haemolymph ofLocusta migratoria

Prophenoloxidase (proPO) was purified from plasma of the locust, Locusta migratoria. This was achieved in three steps (gel filtration on 5300, anion exchange on QMA Memsep, and affinity chromatography on blue Trisacryl) without the use of anticoagulant buffer or inhibitors. The native protein had an apparent molecular mass of 250 kDa as determined by gel filtration and was likely composed of three non-covalently associated subunits of 81 kDa. Its amino acid composition was found to be very similar to that of Bombyx mori proPO. Purified locust proPO could be converted into phenoloxidase (PO) by α-chymotrypsin. Using L-dopa as substrate, Kin and Vmax were determined to be 1.5 mM and 5 μM/s, respectively.