Quantum-dye labeled proteins for glycobiology: a viable nonradioactive alternative tracer

Quantum dye (QD), a macrocyclic europium-chelate, developed as acytological marker, has never been used for quantitative applications. Itwould be ideal, however, if the same tracer can be used for bothqualitative and quantitative purposes. We have labeled some lectins andneoglycoproteins with QD for the purpose of quantitative analyses inglycobiology, and tested its suitability in three different areas inglycobiology: (1) glycosyltransferase, (2) an animal lectin - mannose-binding protein, and (3) the Gal/GalNAc receptor of rat liver membrane.Usefulness of QD-labeled lectins was amply demonstrated by thequantification of galactosyltransferase activity using QD-soybeanagglutinin and QD-RCA120 ( Ricinus communis agglutinin). We also showedthat QD-labeled neoglycoproteins, QD-Man-BSA and QD-Gal-BSA, can replaceradioiodinated counterparts in the binding assays of animal lectins (serummannose binding protein and hepatic Gal/GalNAc receptor.) The advantage ofQD and other europium labels is that it does not decay as radioiodides do.The long shelf-life results in more consistent results from repeatedexperiments.