Disodium p-nitrobenzene phosphate (p-NPP), a widely used phosphatase chromogenic substrate, can form p- nitrophenol under the action of acid phosphatase. Under alkaline conditions, p-nitrophenol is yellow and has a maximum absorption peak at 405 nm. The darker of the yellow product is, the higher of the ACP activity is. Therefore, the activity of ACP can be calculated by measuring the OD value at 405 nm.
