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Assay Method Information

Assay Name:  Biochemical In Vitro Assay
Description:  To generate the enzyme, full length human TPH1 is cloned into the plasmid pET20b(+) (Novagen) and expressed in E. coli. The bacterial cells are ruptured by sonication on ice and the lysate is cleared by centrifugation. The resulting protein in the pellet is re-extracted and TPH1 is purified from the obtained lysate by affinity chromatography using a pterin cosubstrate analog immobilized to the resin of the column. The protein is further purified by size exclusion chromatography to remove protein aggregates. The activity of TPH1 is determined by using a fluorescence assay. The enzyme activity assay is carried out at 15 C. with atmosphere oxygen for the duration of 60 minutes in a volume of 64 μl. The reaction is carried out in a 0.1 M Tris-HCl buffer, adjusted to pH 7.6, containing 1 mM DTT, 0.2 mg/mL catalase, 100 μM ()-6-methyl-5,6,7,8-tetrahydropterine dihydrochloride, 40 μM L-tryptophan, and 40-80 nM of TPH1. The reaction is started by bringing together L-tryptophan with all the other reaction substituents and stopped by quenching with perchloric acid (HClO4). The amount of 5-hydroxy-L-tryptophan produced during the enzymatic reaction is determined by fluorescence readout. Fluorescence, as determined at 540 nm when excited at 300 nm wavelength, increases proportionally to the 5-hydroxy-L-tryptophan formed. Compounds are prepared as 10 mM stock solution in DMSO, then diluted in 384-well plates using DMSO followed by a transfer of the dilutions into the assay plate. Fluorescence is measured for each well and the fluorescence at 540 nm wavelength is compared to the fluorescence of the vehicle in place of compound. Inhibitory activities of example compounds with respect to the TPH1 protein are determined by calculating the IC50 value (the concentration of compound needed to inhibit 50% of the enzyme activity).
Affinity data for this assay
 

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Last update November 1, 2007
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