Determination of kinetic parameters for the metabolism of 2-oxo-clopidogrel by HLMs in the presence of GSH (●), l-Cys (○), and NAC (■). Metabolism of 2-oxo-clopidogrel (2-oxo) was performed in 50 mM potassium phosphate buffer (pH 7.4) with 1 mM reductant and varying concentrations (0–50 μM) of 2-oxo-clopidogrel at 37°C for 30 min, and the amount of 2-oxo-clopidogrel consumed and the products formed were determined with ESI-LC/MS, as described under Materials and Methods. A, kinetic profile for the consumption of 2-oxo-clopidogrel. The amount of 2-oxo-clopidogrel remaining after 30 min of incubation was quantified with ESI-LC/MS, on the basis of a calibration curve prepared with 2-oxo-clopdogrel standards in the same matrix as the samples. The net difference between substrate and 2-oxo-clopidogrel remaining yielded the amount of 2-oxo-clopidogrel consumed. B, kinetic profile for the formation of the total amount of the AM (sum of M2–M5). The relative amount of the AM was calculated as the ratio of the area for m/z 356.1 to that for m/z 322.0. C, kinetic profile for the formation of the AM-thiol conjugates. The relative amount of AM-thiol was calculated as the ratio of the area for MH+ for the AM-thiol conjugate to that for m/z 322.0. The MH+ ions for the AM-NAC and AM-l-Cys conjugates are m/z 517.1 and 475.1, respectively.