Macroglobulin was purified from grass carp plasma by precipitation with polyethylene glycol (PEG)6000, gel filtration and anion-exchange chromatography. The three steps of the procedure resulted in the purification of grass carp plasma α 2M. The purified product was analyzed by polyacrylamide gel electrophoresis (PAGE) under natural conditions and the proteins showed a single band. Meanwhile, it was analyzed by SDS-PAGE under reducing conditions and the proteins showed double bands with molecular weight of about 95 kD and 80 kD. This result demonstrated that grass carp α 2M was composed of two distinct subunits. Most properties of grass carp α 2M were similar to that of human α 2M. Grass carp α 2M treated with trypsin produced the fast-form of the molecule more mobile in PAGE, but the untreated grass carp α 2M had the property of electrophoretically slow-form. α 2M was a nonspecific proteinase inhibitors of blood plasma. Inhibition of activity of Aeromonase hydrophilas extracellular proteinase (AhECPase) showed that grass carp α 2M could inhibit the proteinases secreted from invading bacteria. Double immudiffusion of α 2M demonstrated no cross-antigenicity between grass carp’s and human α 2M .
