Interaction of acid alpha 1-glycoprotein with immunoglobulins.

1. The acid alpha 1-glycoprotein (alpha 1-AGP) immobilized on Sepharose binds selectively only those immunoglobulins (IgG) of total serum proteins which are eluted either with 0.75 m-NaCl or free alpha 1-AGP. 2. alpha 1-AGP, upon partial enzymatic desialination, loses the ability to bind IgG, and does not acquire the ability to bind other serum proteins. 3. The interaction of alpha 1-AGP with IgG or fragments (Fab')2 depends on pH and ionic strength of the medium. At pH 7.2 and ionic strength of 0.15 alpha 1-AGP forms with IgG soluble complexes in which one molecule of IgG binds six molecules of alpha 1-AGP.