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| | Mutant IDH1 Biochemical Assay: LC-MS Detection of 2-HG |
| Description: | Mutant IDH1 R132H catalytic activity was monitored using the quantitative liquid chromatography/mass spectrometry (LC-MS) detection of 2-HG, a product of the NADPH-dependent alpha-KG reduction reaction.More specifically, the biochemical reactions were performed at room temperature in 384-well Greiner flat-bottom plates (Costar, Cat. No. 781201) using a final reaction volume of 30 μL and the following assay buffer conditions: 50 mM HEPES pH 7.4, 10 mM MgCl2, 50 mM KCl, 1 mM DTT, 0.02% BSA, 5 uM NADPH and 100 uM alpha-KG.The final reaction mixture contained 3.3% DMSO and inhibitors with concentrations ranging 0.02-50 μM. The IDH1 enzyme was used at a final concentration of 0.25 nM. Following 45 minutes incubation, the reaction mixtures were quenched by the addition of 10 μL of 16% formic acid containing 800 nM of 5-carbon labeled 13C-2-HG). The protein was then precipitated by the addition of 2.5 volumes of acetonitrile followed by centrifugation (3000×g, 20 minutes). The concentration of 2-HG in the resulting supernatants was measured by LC-MS (see below).LC-MS method. Reaction mixture supernatants were submitted to chromatographic separation on a BiobasicAX column (2.1 mm×20 mm, 5 μm particle, Thermo Scientific Inc.). The chromatographic mobile phases were A) 25 mM ammonium biocarbonate and B) acetonitrile (0.1% ammonium hydroxide). Nicotinamide was eluted at 1 ml/min using a 85-5% B gradient over 0.9 minutes (Agilent 1200SL LC system, Thermofisher LX-4 autosampler) and analyzed by multiple reaction monitoring (MRM) on a API4000 QTrap mass spectrometer (ABSciex, Framingham, Mass.) in the positive electrospray ionization (ESI+) mode. The mass transition for 2-HG and 13C-2-HG were 147→129 and 152→134, respectively. The relative responses (2-HG/13C-2-HG) were measured at varied inhibitor concentrations and used to calculate inhibitory IC50 values (normalized IC50 regression curves). |
| Affinity data for this assay | |
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