Purification and properties of rat alpha 2 acute-phase macroglobulin

Alpha 2 acute-phase macroglobulin was isolated from plasma of turpentine-injected rats. In the method conditions known to damage the biological activities of alpha 2 macroglobulin are avoided. The procedure successively involves: rivanol precipitation, concanavalin A-Sepharose chromatography and ion-exchange chromatography on DEAE-cellulose. Proteolytic activities were minimized throughout the purification. Thus alpha 2 macroglobulin was obtained in a 20% yield and was pure by biochemical and immunological criteria. Its molecular weight appeared to be 760 000 and it consisted of four subunits (Mr 190 000). The protein has an A1cm 1% = 8.8 and an isoelectric point = 4.8. The amino acid and carbohydrate compositions were determined. Our preparations bound 1 molecule of trypsin or 1 molecule of plasmin/molecule of alpha 2 macroglobulin. Kinetic parameters for alpha 2 macroglobulin-bound trypsin and plasmin were determined and compared with those of free trypsin and plasmin using butoxycarbonyl-L-valylglycyl-L-arginine-2-naphthylamide and benzoyl-L-arginine ethylester as substrates.