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. 2014 Oct 14;11(12):4395–4404. doi: 10.1021/mp5004866

Figure 4.

Figure 4

Acetaminophen functions as a weak substrate for NQO2. (a) NQO2 in vitro inhibition assay. NQO2 was incubated in the presence of compounds at the concentrations indicated and NQO2 activity measured with a colorimetric assay. (b) NQO2 substrate assay. Substrate activities of menadione (25 μM), APAP (2.5 mM), AMAP (2.5 mM), and control (DMSO) are shown. All substrate activities were abolished by addition of quercetin (10 μM). (c) Kinetic analysis of NQO2 substrate activity with menadione (left) and acetaminophen (right). Red lines represent 95% confidence intervals of the fitted ligand binding curves (black). NQO2 activity was measured with increasing substrate concentrations at fixed enzyme and cosubstrate (500 μM NMEH) concentrations. Michaelis constants and maximum reaction rates are displayed with standard errors. Note that acetaminophen and menadione were dissolved in the assay buffer in order to omit DMSO (N = 3 in all panels).