CYTOPHOTOMETRIC DETERMINATION OF ALKALINE PHOSPHATASE ACTIVITY OF INDIVIDUAL NEUTROPHILIC LEUKOCYTES WITH A BIOCHEMICALLY CALIBRATED MODEL SYSTEM

A model system consisting of polyacrylamide films into which cell sonicate is incorporated was applied to investigate quantitative aspects of the cytochemical azo dye coupling method for alkaline phosphatase activity in neutrophilic leukocytes. The films were assayed in media containing naphthol AS-MX phosphate and 4-aminodiphenylamine diazonium sulfate. Optimal reaction conditions under which proportionality existed between the amount of reaction product and incubation time or enzyme concentration were determined. Since the enzyme activity in the films could also be measured chemically, using disodium phenyl phosphate as a substrate, a direct relation between the cytochemical and biochemical activity could be established. The azo dye coupling method was applied for the quantification of the enzyme activity. Air-dried microscopic preparations of exudate neutrophils were stained and the amount of dye formed in the cytoplasm of individual leukocytes was measured with a cytospectrophotometer based on the two-wavelength principle. By reference to the relation between biochemical and cytochemical activities in the model films, the cytochemically determined enzyme activity could be expressed in biochemical units. Independently, the average alkaline phosphatase activity per cell was determined by direct biochemical assay of the leukocyte suspension. The results showed that about 60% of the biochemically assayed activity in sonicate was demonstrated in the cell preparations by the cytochemical staining method. The discrepancy between the results of the two methods is discussed. The applicability of the model system for elucidation of the relationship between the results of cytochemical and biochemical enzyme determination in cells is stressed.