Mechanisms of metal--salt methods in enzyme cytochemistry with special reference to acid phosphatase.

This review is concerned with theoretical and experimental aspects of the factors governing the localizing potentialities of cytochemical enzyme reactions that are based on the metal-salt principle, that is, the precipitation of the primary product of the enzymatic reaction by a heavy-metal ion at the enzymatic site. Special attention is given to the lead phosphate precipitation process in acid phosphatase cytochemistry. The various model systems developed for the study of the factors involved in precipitation are described and their advantages and disadvantages discussed. Furthermore, the various cytochemical methods so far used for the demonstration of acid phosphatase activity are critically evaluated in the light of the results obtained with the model systems.