FLOW CYTOFLUOROMETRIC ANALYSIS OF ENZYME-REACTIONS IN INDIVIDUAL CELLS

Cytochemical methods available for flow cytofluorometric analysis of enzyme reactions in individual cells are reviewed. Methods for hydrolytic enzymes such as esterases, glycosidases, phosphatases and proteinases are based on the principle that the reaction product after hydrolysis is fluorescent whereas the substrate is not. Peroxidase activity can be demonstrated with monomeric homovanillic acid as substrate which is converted into its dimer which is highly fluorescent. Oxidoreductases can be analysed by measuring the formation of NAD(P)H or by the use of tetrazolium salts yielding fluorescent formazans. A new approach is the indirect analysis of formazan production which quenches autofluorescence of cells in a dose-dependent manner and the decrease in fluorescence is a measure for cellular dehydrogenase activity.