Assay Method Information

Assay Name:  Inhibitory Activity
Description:  To detect thyroid peroxidase (TPO) inhibitory activity, the production of hypoiodous acid (HOI) was quantified. HOI was detected by reacting it with methionine, which is converted to dehydro-methionine, which in turn is detected by reacting it with excess iodide at acidic pH. The reaction converts I− to I3 − that has absorbance at 353 nm. In brief, 0.6 μL compound serially diluted in DMSO was added to 25 μL 50 nM baculovirus-expressed recombinant human TPO (obtained from RSR Ltd, Cardiff, UK) in assay buffer (100 mM Na2HPO4/NaH2PO4, pH 7.4), after which absorbance at 353 nm was read to obtain a blank value. The enzyme reaction was initiated by the addition of 25 μL of a mix consisting of 2 mM methionine, 20 μM NaI and 100 μM H2O2 in assay buffer, and stopped by the addition of 10 μL catalase, 0.25 mg/mL. After an additional 5 min, 25 μL 600 mM sulphuric acid followed by 25 μL 100 mM KI were added, and absorbance at 353 nm was read 5 min after this addition. IC50 values of the compounds tested were obtained using standard procedures.In general, the compounds disclosed herein, which were tested, had a surprisingly high selectivity for the MPO enzyme over the TPO enzyme within the range of 220-1600 for the ratio IC50 (TPO)/IC50 (MPO).
Affinity data for this assay
 

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