A new dynamic model system for the study of capture reactions for diffusable compounds in cytochemistry. II. Effect of the composition of the incubation medium on the trapping of phosphate ions in acid phosphatase cytochemistry.

A model system developed for the study of the dynamics of capture reactions for diffusable compounds in cytochemistry served as a basis for the experiments reported in the present paper. The model was used to study the effect of the composition of the cytochemical medium on the trapping of phosphate ions by lead (II) ions in acid phosphatase cytochemistry. In this system a phosphate-containing solution and a lead-containing solution (cytochemical medium) are pumped along opposite sides of a polyacrylamide film. The phosphate concentration at which measurable precipitation starts in the film (critical phosphate concentration) was taken as a measure of the trapping efficiency of the cytochemical medium. The addition of beta-glycerophosphate and cytidine-5'-monophosphate to a buffered lead-containing solution resulted in a higher critical phosphate. The addition of chloride ions and acetone, as well as decreasing the molarity of the acetate buffer of the cytochemical medium, were found to lower the critical phosphate concentration, whereas the addition of fluoride ions, glucose, and sucrose had no effect. From the effect of variations in the composition of the cytochemical medium on the trapping efficiency and the turnover number of acid phosphatase in the medium, it was possible to predict which cytochemical medium would be the most suitable for the demonstration of acid phosphatase activity in guinea-pig peritoneal exudate cells. The results were in accordance with the localization of acid phosphatase activity: the higher the trapping efficiency and the turnover number, the higher the amount of precipitate and the number of positive enzymatic sites. In this way an improved cytochemical medium for acid phosphatase was developed.