Fluorometric determination of sugars using fluorescein-labeled concanavalin A-glycogen conjugates

The fluorescence of fluoresceinisothiocyanate-labeled concanavalin A (FITC-Con A) was quenched by forming an FITC-Con A-glycogen conjugate and dequenched upon addition of sugars to the conjugate solution due to disaggregation of the conjugate. However, fluorescence quenching was barely observed upon formation of FITC-Con A-dextran conjugate. The sugar-induced fluorescence response of the FITC-Con A-glycogen conjugate depended significantly on the type of sugar: methylated alpha-D-glucose and alpha-D-mannose both induced high and rapid responses, while the responses to D-mannose and D-glucose were moderate. In contrast, no response was observed in the presence of D-galactose due to a lack of affinity to Con A. Thus, it is apparent that D-glucose and other sugars can be detected via the fluorescence of the FITC-Con A-glycogen conjugate.