Involvement of sialic acid residues in electroimmunodiffusion of alpha 1-acid glycoprotein. A method for determining the degree of sialylation of serum glycoproteins.

When the two immunological methods, radial immunodiffusion (RID) and electroimmunodiffusion (EID), were used for the determination of alpha 1-acid glycoprotein, a significant discrepancy in the results was encountered depending on the degree of sialylation. It appeared that with desialylated alpha 1-acid glycoprotein, amounts estimated by EID were much lower than those actually present as assayed by the RID method. Determination of glycoprotein samples treated with neuraminidase for varying periods of time revealed an increasing underestimation by the EID method with decreasing sialic acid content. Partial resialylation of asialo-alpha 1-acid glycoprotein by bovine colostrum beta-galactoside alpha (2 leads to 6) sialyltransferase on the other hand resulted in less underestimation. Differential determination of alpha 1-acid glycoprotein by the two immunological methods thus offers a method for the estimation of the degree of sialylation of alpha 1-acid glycoprotein and other sialoglycoproteins in serum and body fluids.