USE OF FLUORESCEIN-DI-BETA-D-GALACTOPYRANOSIDE (FDG) AND C-12-FDG AS SUBSTRATES FOR BETA-GALACTOSIDASE DETECTION BY FLOW-CYTOMETRY IN ANIMAL, BACTERIAL, AND YEAST-CELLS

Fluorescein-di-beta-D-galactopyranoside (FDG) was found to be a useful substrate for beta-galactosidase detection by flow cytometry in gram- negative bacteria, since it entered viable cells and gave a fluorescen ce emission proportional to the enzymatic activity. C-12.FDG, a more l ipophilic derivative, gave a very poor signal because of the lack of p enetration. On the contrary, C-12.FDG was more sensitive than FDG for beta-galactosidase activity determinations in animal cells. In contras t to previous reports, C-12-FDG did not enter viable yeast cells, so t hat the use of the substrate required cell permeabilization. Without t his treatment, C-12.FDG penetrates only nonviable yeast cells that may occur in populations expressing beta-galactosidase.