A NEW HISTOCHEMICAL METHOD FOR ACID PHOSPHATASE BY THE USE OF 5-IODOINDOXYL PHOSPHATE

Abstract

5-Iodoindoxyl phosphate has been found to be a useful indigogenic substrate in the histochemical demonstration of acid phosphatase activity. Its superiority to other indoxyl phosphates is apparently due to a rapid oxidation of 5-iodoindoxyl to 5,5'-diiodoindigo in the acid pH range. A redox system of ferri-ferrocyanide enhances the oxidation and improves the localization. This method can be applied to calcium-formol-fixed tissues or to fresh frozen sections, although fixed tissues yield better results. The method is not recommended for the demonstration of enzyme activity in lipid-rich tissues because of the complexing property of lipids with 5,5'-diiodoindigo that results in crystal formation. The distribution of acid phosphatase activity with this method is generally similar to that obtained using azo dye methods.