Residual α 2-macroglobulin in fetal calf serum and properties of its complex with thrombin

Abstract

Summary Active α2-macroglobulin (α2M) has been shown to persist in commercial preparations of fetal bovine serum. Reaction with trypsin and the mitogenic protease thrombin leads to cleavage of the polypeptide chain of α2M, with simultaneous conversion to a fast electrophoretic form. The trapped protease is fully active toward low molecular weight synthetic substrates, but reacts slowly if at all with the protein inhibitor hirudin (M.W. 12,200). Addition of methylamine to fetal bovine α2M leads to covalent incorporation of the amine into the protein, but the subsequent and apparently spontaneous conversion from the slow to the fast electrophoretic form seen with human α2M is not observed. Sedimentation velocity studies of intact and modified fetal bovine α2M show that a small shape change results from reaction with proteases but that, in contrast to the human protein, no shape change results from reaction with methylamine.