A fluorescent probe for selective detection of lysosomal β-hexosaminidase in live cells.

Determining the activity of lysosomal β-hexosaminidase in cells is of great importance for understanding the roles that these enzymes play in pathophysiological events. Herein, we designed the new fluorescent probe, βGalNAc-Rhod-CM(NEt), which consisted of a βGalNAc-linked rhodol unit serving as a β-hexosaminidase reactive fluorogenic moiety and a N,N'-diethylaminocoumarin (CM(NEt)) group acting as a fluorescence marker for determining the degree of cell permeabilization. Treatment of βGalNAc-Rhod-CM(NEt) with β-hexosaminidase promoted generation of Rhod-CM(NEt), thereby leading to an increase in the intensity of fluorescence of Rhod. However, this probe did not respond to the functionally related glycosidase, O-GlcNAcase. The detection limit of βGalNAc-Rhod-CM(NEt) for β-hexosaminidase was determined to be 0.52 nM, indicating that it has high sensitivity for this enzyme. Furthermore, the probe functioned as an excellent fluorogenic substrate for β-hexosaminidase with k and K values of 17 sec and 22 μM, respectively. The results of cell studies using βGalNAc-Rhod-CM(NEt) showed that levels of β-hexosaminidase activity in cells can be determined by measuring the intensity of fluorescence arising from Rhod and that the intensity of fluorescence of CM(NEt) can be employed to determine the degree of cell permeabilization of the probe. Utilizing the new probe, we assessed β-hexosaminidase activities in several types of cells and evaluated the effect of glucose concentrations in culture media on the activity of this enzyme.