In recent years fluorescence techniques have become increasingly popular
for the estimation and localization of enzymatic activities. Basic methodological
concepts on enzyme histochemistry can be found in standard books and reviews [1 - 6].
Enzyme activity studies may be carried out to assess the localization of enzymes within
cells and tissues, and to determine the effects of pH, ionic strength, temperature,
presence of inhibitors, etc., on the rate of an enzyme-catalyzed reaction. In addition,
enzymes can be applied as histochemical reagents to remove macromolecular
substrates, examples being RNases, DNases, amylases, etc., or to identify substrates
after their fluorescent labeling. Chromo- and fluorogenic reactions are usually
employed to reveal enzymatic activity. A relevant issue to avoid diffusion artifacts or
false localization is that the colored or fluorescent product of a given enzymatic
reaction must have very scarce or null water solubility. However, insoluble or
crystalline precipitates should be not confused with specific cell structures. Some
examples will illustrate these points.
Keywords: AEC, Arylsulfatases, Benzothiazole-hydroxystyrene, CARD,
Caspases, Cathepsins, Dehydrogenases, ELF, Esterases, Fluorogenic substrates,
Glycosidases, Indigogenic methods, Peroxidases, Phosphatases, Tyramide signal
amplification.