[Studies on the reaction of wheat germ agglutinin with serum glycoproteins. Lectins as reagents. III].

Solutions of wheat germ agglutinin exclusively but incompletely react with serum glycoproteins containing N-acetylneuraminic acid, viz. alpha 2-macroglobulin, haptoglobin, haemopexin, immunoglobulin A, alpha 1-acid glycoprotein, ceruloplasmin, immunoglobulin M (in decreasing order) and others. The precipitation does not proceed stoichiometrically and depends on lectin and polyethyleneglycol concentration, temperature, pH-value, ionic strength, and matrix effects. Presumedly, the reaction is initiated by specific and electrostatic interactions of wheat germ agglutinin with sialic acid residues of the glycoprotein and followed by binding of N-acetylglucosamine residues. A minimal precipitation of albumin is due to its complex formation with glycoproteins via disulphide bonds. Although wheat germ lectin precipitation sensitively detects serum sialoproteins, its intensity does not reflect the amount of N-acetylneuraminic acid in serum glycoproteins, thus calling in question the analytical use of this lectin for the measurement of sialoglycoconjugates.