LEAD AND PHOSPHATE AS SOURCES OF ARTIFACT IN NUCLEOSIDE PHOSPHATASE HISTOCHEMISTRY

The contribution of lead and lead phosphate binding to tissue as a possible source of artifact in the Wachstein-Meisel histochemical procedure was considered. In addition, the relevance of lead-catalyzed substrate hydrolysis in tissue water and in the reaction media, as well as the efficacy of the enzyme inhibitors, para-mercurobenzoate and potassium fluoride were examined. Lead-catalyzed hydrolysis of substrate in tissue water does not play a significant role in reaction product deposition. Lead-catalyzed hydrolysis in the reaction media does produce significant amounts of lead phosphate. Furthermore, the enzyme inhibitors in addition to inhibiting enzyme activity alter lead binding to tissue, precipitate lead from solution and decrease tissue staining. Loss of tissue staining may result from a decrease in phosphate-trapping efficiency of lead when the free lead ion concentration is lowered in the reaction medium. Lead phosphate and lead localize as deposits of electron-dense material at tissue sites parallel to those observed with the complete Wachstein reaction mixture. It is concluded that tissue and chemical events other than enzyme activity may contribute to reaction product localization.