PROBLEMS OF ENZYMATIC LOCALIZATION BY CHEMICAL REACTIONS APPLIED TO TISSUE SECTIONS

Abstract

1. During the preparation of the tissues for histochemical studies, attention must be directed toward the conservation of enzymatic activity and the maintenance of enzyme localization. No matter which technique is employed, the histological manipulation can result in either false positive or false negative enzyme localization. 2. The special characteristics of the chemical reactions used for the demonstration of enzymes in tissue sections have been listed, and an analysis of the desired properties of each constituent has been made. 3. When the tissue sections are introduced into the incubation medium new problems arise which are related to the properties of both the enzyme being studied and the chemical reagents being used. 4. Theoretical arguments have been presented to indicate that the discrete deposition of the dye within the cell does not necessarily represent a more accurate localization for all enzymes, than does the widespread dispersion of the dye throughout the cells. 5. Although we have some understanding of the ideal properties of the substrate, the split product, and the final pigments, there are many situations where these cannot be attained. Nevertheless, by the selection of the proper combination of suboptimal conditions, an accurate localization of many enzymes can be achieved.