Abstract
.alpha.2M (.alpha.2-macroglobulin) was purified from human plasma by 2 different procedures. As well as having no detectable impurities by the usual criteria for testing the homogeneity of protein preparations, these .alpha.2M preparations showed a single component, after reduction in urea, of 185,000 daltons by sodium dodecyl sulfate/polyacrylamide-gel electrophoresis. The MW of the .alpha.2M was 718,000 by sedimentation-equilibrium experiments by using the gravimetrically determined .hivin.v [partial specific volume] of 0.731 ml/g. The interaction of several proteinases with .alpha.2M was studied by using a novel discontinuous polyacrylamide-gel system, which showed clear separation of the enzyme-complexed .alpha.2M from the free .alpha.2M. Urokinase, as well as trypsin, chymotrypsin, plasmin and thrombin apparently forms complexes with .alpha.2M. The cleavage of the 185,000-dalton subunit to a 85,000-dalton species on interaction of trypsin with .alpha.2M was demonstrated by sodium dodecyl sulfate/polyacrylamide-gel electrophoresis after reduction of the .alpha.2M-trypsin complex in urea. The amino acid composition, carbohydrate content, absorption coefficient at 280 nm, the specific refractive increment and the sedimentation coefficient for these .alpha.2M preparations were measured. The stability of the trypsin-binding activity of the .alpha.2M preparations was also studied under several storage situations.