[Structural changes in the sugar chains of gamma-glutamyltranspeptidase by malignant transformation]

Abstract

Structures of the sugar moieties of gamma-glutamyl transpeptidases purified from the kidney and the liver of rat, mouse, and cattle were studied after being chemically released as oligosaccharides. The results indicated that both organ-specific and species-specific differences exist in the sugar chains of the enzyme. Comparative studies of sugar chains of the heavy and light subunits of the rat kidney enzyme revealed that high mannose-type sugar chains are found only in the heavy subunit. By the same analysis of the oligosaccharide fractions obtained from four isozymic forms of the rat kidney enzyme, it was found that all these enzymes contain 2 mole of neutral sugar chains but different numbers of acidic sugar chains in one molecule. Comparative studies of oligosaccharides obtained from the enzymes purified from rat AH-66 hepatoma and from normal rat liver revealed that more than 40% of the sugar chains of the hepatoma enzyme contain bisecting N-acetylglucosamine residues which are not found in those of the liver enzyme. By making use of the structural changes associated with malignant transformation, a new diagnostic method or hepatoma was developed. In principle, the method consists of affinity chromatography of the desialylated serum enzyme using an erythroagglutinating lectin agarose column.