Which substrate is characteristic for alkaline phosphatase (ALP) in luminescent assays?

• A. Luminol
• B. Dioxetane phosphate
• C. Acridinium ester
• D. Luciferin

Answer: (B)

Alkaline phosphatase works by removing phosphate groups, and in luminescent assays the substrate is designed so that this dephosphorylation triggers light emission. Dioxetane phosphate fits this idea perfectly: when ALP cleaves the phosphate, the dioxetane moiety is activated and decomposes to produce chemiluminescence that can be measured.

Luminol, acridinium esters, and luciferin are used in other types of chemiluminescent or bioluminescent systems, not as the standard ALP substrates. Luminol is common with peroxidases, acridinium esters serve as labels in certain immunoassays, and luciferin requires luciferase. Hence, dioxetane phosphate is the substrate that characteristically works with ALP in luminescent assays.