A NEW METHOD FOR THE INVESTIGATION OF THE KINETICS OF THE CAPTURE REACTION IN PHOSPHATASE CYTOCHEMISTRY I. THEORETICAL ASPECTS OF THE LOCAL FORMATION OF CRYSTALLINE PRECIPITATES

Abstract

Factors governing the precipitation kinetics and localization of lead phosphate in phosphatase cytochemistry are discussed, with special attention to the origin of diffusion artifacts. The principal differences between the kinetics of coupling reactions leading to insoluble organic dyes and of lead salt methods are treated in terms of the physicochemical theory of crystallization of sparingly soluble salts. This process, since it involves nucleation and crystal growth, is dependent on supersaturation and the presence of heterogeneous catalysts in the reaction medium. Under cytochemical conditions in tissue sections these factors are partially determined by the lead concentration in the medium and the local specific enzyme activity. It is postulated that heterogeneous nucleation of phosphate ions which have escaped from their enzymatic production sites may be a source of falsely localized precipitates. The need for experimental models for the study of the dynamics of precipitation and diffusion is stressed.