The Binding of Lithium Carmine to a2-Macroglobulin

The colloidal dye lithium carmine was added in vitro to normal human serum. Electrophoretic experiments showed that the dye was associated mainly with a2-globulins, small amounts with the albumin and only traces with the y-globulins. The main complex was eluted with the macroglobu­ lin peak obtained by gel filtration on Sephadex G-200 and sedimented in the heavy fraction on density gradient ultracentrifugation. The dye-protein complex could be precipitated with an anti­ serum specific for a2-macroglobulin. Gel filtration of a solution of pure ct2-macroglobulin, to which lithium carmine was added, demonstrated that the dye was bound to this protein.