5-Bromo-6-chloro-3-indoxyl phosphate p-toluidine salt, also known as Magenta-phos p-toluidine salt, is a histochemical substance used for visualizing areas of alkaline phosphatase activity. Hydrolysis of the phosphate group on 5-Bromo-6-chloro-3-indoxyl phosphate by alkaline phosphatase generates an insoluble indigo compound. The indoxyl species resulting from phosphate hydrolysis of related compounds can be reacted with tetrazolium salts, reducing the tetrazolium to a colorful insoluble formazan species. A solubilization technique involving reduction of the insoluble hydrolytic product of the closely related 5-Bromo-4-chloro-3-indoxyl phosphate permitted the use of this substrate in quantitative ELISA experiments. 5-Bromo-6-chloro-3-indolyl phosphate, p-toluidine salt is a substrate of TNAP.
