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Assay Method Information

Assay Name:  ENPP1 Activity Assay
Description:  Selected compounds of Table 1, Table 2 and other derivatives were prepared and assessed in an ENPP1 activity assay using thymidine monophosphate paranitrophenol (TMP-pNP) as a substrate. Enzyme reactions were prepared with TMP-pNP (2 μM), 5-fold dilutions of ENPP1 inhibitor, and purified recombinant mouse ENPP1 (0.5 nM) in 100 mM Tris, 150 mM NaCl, 2 mM CaCl2, 200 μM ZnCl2, pH 7.5 at room temperature. Reaction progress was monitored by measuring absorbance at 400 nm of paranitrophenolate produced by the reaction for 20 minutes. Slopes of product formation were extracted, plotted, and fit to obtain IC50 values with Graphpad Prism 7.03. Compounds were also assessed in an ENPP1 enzyme activity assay using 32P cGAMP as a substrate. Radiolabeled32P cGAMP was synthesized by incubating unlabeled ATP (1 mM) and GTP (1 mM) doped with 32P-ATP with 2 μM purified recombinant porcine cGAS in 20 mM Tris pH 7.5, 2 mM MgCl2, 100 μg/mL herring testes DNA overnight at room temperature, and the remaining nucleotide starting materials were degraded with alkaline phosphatase for 4 h at 37° C. The probe 32P-cGAMP (5 μM) was incubated with purified recombinant mouse ENPP1 (20 nM) in 100 mM Tris, 150 mM NaCl, 2 mM CaCl2, 200 μM ZnCl2, pH 7.5 at room temperature for 5 hours. To generate enzyme inhibition curves, 5-fold dilutions of ENPP1 inhibitor were included in the reaction. Degradation was evaluated by TLC (as described by Li et al. Nat. Chem. Biol. (2014) 10:1043-8). Plates were exposed on a phosphor screen (Molecular Dynamics) and imaged on a Typhoon 9400 and the 32P signal was quantified using ImageJ. Inhibition curves were fit to obtain IC50 values using Graphpad Prism 7.03.
Affinity data for this assay
 

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