Determination of sialic acid residues in transferrin by oxidative-reductive immunoassay

A method is described for the determination of sialic acid residues in glycoproteins displaying microheterogeneity in the sugar residue. The new method is based on combining an oxidative-reductive step with binding of the glycoprotein to an immunoadsorbent. After a mild oxidation with sodium metaperiodate the sugar is reduced with labeled sodiumborotritide. The chemical modification of the sugar residues does not seem to impair the binding of glycoprotein to the immunoadsorbent. The procedure, which has been elaborated for human transferrin, can be carried out in the presence of other substances in body fluids.