Abstract
Here we describe a protocol for the identification of effectors of tissue-nonspecific alkaline phosphatase (TNAP). It is based on a highly sensitive method for detecting TNAP activity. After dephosphorylation by TNAP, a dioxetane-based substrate undergoes a series of chemical transformations resulting in light production. Light intensity serves as a quantitative measure of the velocity of the TNAP-catalyzed reaction in the steady state. This protocol includes guidelines for optimizing the assay and for high-throughput screening in multiwell plates. The assay is sensitive to the influence of diverse effectors of TNAP as long as the assay optimization steps are repeated for each new batch of the enzyme; full optimization is accomplished in under 2 d. Depending on the available equipment, 10,000-100,000 compounds can be screened in an 8-h period. This protocol provides a method of screening TNAP that is 1,000-fold more sensitive and 10-fold faster than a conventional colorimetric assay with p-nitrophenyl phosphate.