Immunoassay of glycosylated proteins employing antibody directed to reductively glycosylated N-terminal amino acids

An immunoassay for a protein that is non-enzymatically glycosylated on the alpha amino group of its N-terminal amino acid, the immunoassay comprising: providing a sample containing the glycosylated protein; reacting the glycosylated protein with a reducing agent so that the sugar residue on the N-terminal amino acid is reduced; contacting the reduced glycosylated protein with an antibody directed to Glc-ol-X which is prepared by immunizing an animal with an immunogen of the formula (Glc-ol-X-L)n-carrier; and detecting or quantitating the reduced glycosylated protein bound to the antibody. In the formula (Glc-ol-X-L)n-carrier: X is the N-terminal amino acid of the glycosylated protein, except that X cannot be lysine; L is a bond or a linker group; Glc-ol is the reduced form of the sugar attached to X on the glycosylated protein, and Glc-ol is attached to the alpha amino group of X; the carrier is an immunogenic compound other than the glycosylated protein; and n is from 1 to the number of available coupling sites on the carrier. Also, the antibody, the immunogen, and methods of making them. Finally, a kit for quantitating a protein glycosylated on its N-terminal amino acid.