| Assay Method Information | |
| | Enzymatic Assay |
| Description: | TDO2: Recombinant human TDO comprising amino acids 19-407 with a N-terminal hexahistidine tag expressed in E. coli and purified to homogeneity is incubated at a final concentration of 15 nM in assay buffer consisting of 75 mM phosphate buffer at pH7 supplemented with 100 μM ascorbic acid, 50 U/ml Catalase, 0.01% BSA, and 0.01% Tween 20 (protocol modified from Seegers et al, JBS 2014). Example compounds are serially diluted in DMSO, further diluted in phosphate buffer, and added to the reaction mixture at final concentrations ranging from 10 μM to 0.5 nM. The final DMSO concentration is 0.6%. Following a pre-incubation of 30 minutes at RT, the reaction is started by the addition of L-tryptophan at a final concentration of 200 μM in assay buffer. After 30 minutes of incubation at RT, 3 μL of the reaction mixture are transferred to a 384 deep well plate containing 25 μL of deionized water. 100 μl of 200 nM L-Tryptophan-(indole-d5) in cold 100% methanol are added followed by a 10 minutes centrifugation at 4,000 rpm at 4° C. An additional 75 μL of deionized water are then added and followed by a 10 minutes centrifugation at 4,000 rpm at 4° C. The product of the reaction N′-Formylkynurenine (NFK) is quantified by LCMS and normalized to the L-Tryptophan-(indole-d5) signal. Samples with 0.6% DMSO (0% effect) and a TDO/IDO inhibitor (100% effect) are used as control samples to set the parameters for the non-linear regression necessary for the determination of the half-maximal inhibitory concentration (IC50) for each compound. For each compound concentration the percentage of activity compared to 0% and 100% effect is calculated as average±STDEV (each concentration measured in duplicate). IC50 values and curves are generated with XLfit software (IDBS) using Dose-Response One Site model 203 (four parameter logistic curve model). When compounds are measured multiple times, mean values are given. |
| Affinity data for this assay | |
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