| Assay Method Information | |
| | Enzymatic TDO Assay |
| Description: | The IC50 values for each compound were determined by testing the activity of TDO in a mixture containing 50 mM potassium phosphate buffer at pH 6.5; 200 nM purified human TDO protein, 20 μM L-tryptophan, 20 mM ascorbate 0.1% DMSO. Differently from the IDO activity assay, no methylene blue is added to the assay. The inhibitors were initially diluted in DMSO at 100 mM and were diluted in potassium phosphate 50 mM, added to the reaction mixture at final concentrations raging from 30 μM to 5 nM and preincubated with the enzyme for 5 min at 25° C. The reaction was started by addition of L-tryptophan to 20 μM and incubated 15 min at 37° C. The reaction was stopped by addition of 0.5 vol of 30% trichloroacetic acid and incubated 30 min at 60° C. to hydrolyze N-formylkynurenine to kynurenine. The reaction was centrifuged at 3400 g for 5 min to remove precipitated protein and the supernatant was reacted with 2% (w/v) of p-dimethylaminobenzaldehyde in acetic acid. The reaction was incubated 10 min at 25° C. and read at 480 nm in a spectrophotometer. Control samples with no TDO inhibitor, or with no TDO enzyme were used as controls to set the parameters for the non-linear regressions necessary for determination of the IC50 for each compound. Nonlinear regressions and determination of the IC50 values were performed using the GraphPad Prism 4 software. |
| Affinity data for this assay | |
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