Detection, purification and characterization of a human cancer-associated galactosyltransferase acceptor

A low-molecular-weight acceptor of galactosyltransferase activity was detected in sera and effusions of patients with extensive maligant disease. This substance was purified to homogeneity from both human serum and effusion by using sequential charcoal/Celite and DEAE-cellulose column chromatography. The purified acceptor was shown to act as substrate for both purified normal and cancer-associated human galactosyltransferase (EC 2.4.1.22) isoenzymes, but had a higher affinity for the cancer-associated isoenzyme (K(m) = 20 μM) than for the normal isoenzyme (K(m)=500μM). The substrate was found to be a glycopeptide with mol.wt. approx. 3600 determined by polyacrylamide-gel chromatography. Carbohydrate analysis demonstrated only the presence of glucosamine and mannose. Amino acid analysis revealed that the peptide moiety consisted of eight different amino acids, including two residues of asparagine and one residue of serine, but no threonine. These structural data suggest that the acceptor is a fraction of an asparagine-glucosamine type of glycoprotein.