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| | ACCase Enzymatic Assay |
| Description: | Ustilago maydis acetyl CoA carboxylase (ACCase) was cloned, expressed, and purified as described (Weatherly et al, Biochem. J., 2004) and the test compounds were tested in a 96-well plate format. Primary in vitro screening consisted of obtaining dose response data at 100, 33, 10, and 1 μM inhibitor. Actives in the primary screen were re-tested to establish IC50 values.Direct detection of the conversion of acetyl CoA to malonyl CoA by ACCase was not feasible, but during this process ATP is converted to ADP which allowed for detection through a standard reaction coupling with ADP recycling to the oxidation of NADH. Thus, ACCase activity was measured via kinetic OD340 measurements of the conversion of NADH to NAD in a coupled reaction involving the conversion of phosphoenolpyruvate (PEP) to lactate.The complete 200 ul reaction mixture contained 52.5 mM HEPES (pH8), 2.625 mM MgCl2, 1 mM ATP, 0.525 mM DTT, 11 mM NaHCO3, 1% DMSO with or without inhibitor, 1× pyruvate kinase/lactate dehydrogenase (PK/LDH), 0.3 mM NADH, 0.5 mM PEP, and 5 μg ACCase. The reactions were incubated at 30° C. for 10 minutes and then initiated by the addition of 0.33 mM acetyl CoA. The initiated reactions were read immediately via plate reader at OD340 and kinetic readings were acquired every 20 s for 15 minutes while keeping the temperature at 30° C.A slope of the kinetic curve was determined by using the 2 to 7 minute data which was then calculated as percent inhibition relative to the no inhibitor control.The primary screens were conducted in duplicate and the IC50's conducted in triplicate. Averages were reported along with standard deviation calculation to generate error bars.Each plate contained its own controls and consisted of a DMSO only control, 5-fold titration series of soraphen from 2 μM to 3.2 nM, and an ADP coupled reaction control.In order to effectively screen out non-specific modulators of pyruvate kinase and lactate dehydrogenase (the coupled portion of the reaction), a PK/LDH inhibition test was developed. The complete 200 μl reaction mixture contained 52.5 mM HEPES (pH8), 2.625 mM MgCl2, 0.525 mM DTT, 11 mM NaHCO3, 1% DMSO with or without inhibitor, 1× pyruvate kinase/lactate dehydrogenase (PK/LDH), 0.3 mM NADH, and 0.5 mM PEP. The reactions were incubated at 30° C. for 10 minutes and then initiated by the addition of 66 μM ADP. The initiated reactions were read immediately via plate reader at OD340 and kinetic readings were acquired every 20 s for 15 minutes while remaining at 30° C.A slope of the kinetic curve was determined by using the 2 to 7 minute data which was then calculated as percent inhibition relative to the no inhibitor control. Those compounds which had no significant PK/LDH inhibition at or above the IC50 in the ACCase assay, were considered to be valid modulators of only ACCase. |
| Affinity data for this assay | |
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