3-Indoxyl phosphate is a chromogenic and electrochemical substrate for alkaline phosphatase.1,2 Upon enzymatic cleavage by alkaline phosphatase, 3-indoxyl is released and subsequently oxidized to produce water-insoluble indigo, which can be quantified by colorimetric detection at 660 nm as a measure of alkaline phosphatase activity.1 3-Indoxyl phosphate can also be converted to water-soluble leucoindigo by reduction of indigo in alkaline solution by sodium dithionite, which can be quantified by colorimetric detection at 415 nm or voltametric detection as a measure of alkaline phosphatase activity.2 3-Indoxyl phosphate has been used in ELISAs.
1.Tsou, K.C., and Su, H.C.F.A new colorimetric method for the determination of alkaline phosphatase with indoxyl phosphateAnal. Biochem.11(1)54-64(1965) 2.Fanjul-Bolado, P., GonzÁlez-GarcÍa, M.B., and Costa-GarcÍa, A.Detection of leucoindigo in alkaline phosphatase and peroxidase based assays using 3-indoxyl phosphate as substrateAnal. Chim. Acta534(2)231-238(2005)