Human liver cytosol, HCY (20 μM), and acrolein (10, 50 μM) were preincubated at 37°C for 2 min and then the reaction was initiated with the addition of NAD (0.5 mM) and stopped after 5 min. Control incubations contained no exogenously added acrolein. Because acrolein is formed chemically from HCY during the incubations, the actual acrolein concentrations were measured at the beginning and the end of the incubations. The actual mean acrolein concentrations at the beginning and the end of the incubations were 5, 15, and 55 μM in the control incubation and in the incubations with the addition of 10 and 50 μM acrolein exogenously, respectively.