Hepa-1 cells were grown to >95% confluence. After adding 10 ml of fresh medium, the cells were incubated in the presence of OT or UVT (100 μM) or TCDD (2 nM) for a total of 4 h. TCDD was added in dimethyl sulfoxide (final concentration of dimethyl sulfoxide was 0.02%). Cycloheximide (5-μg/ml medium) was added during the final 2 h of oxidized tryptophan treatment. After the end of incubation, the cells were washed two times with sterile PBS and incubated for an additional period of 3 h in fresh medium (10 ml) containing actinomycin D (1 μg/ml). The cells were then washed with ice-cold PBS, scraped, collected by centrifugation, and EROD activity was determined as described in the text.

• ↵1-a EROD activity is expressed as picomoles of resorufin formed/milligram protein/min ± S.D.

• ↵1-150  Significantly different from the untreated control group (P < .01).

• ↵1-160  Significantly different from the respective group where no cycloheximide was added (P < .01).