Incubation conditions and assay technique were as described in Table 2. Microsomes contained 0.14 nmol of CYP1A1/mg or 0.19 nmol of CYP1A2/mg). Inhibition was determined by comparing catalytic activity in aliquots from primary reaction mixtures with carrier to that in aliquots of primary reaction mixtures containing TCB, but not NADPH. Rate constants (k) were determined from a linear regression analysis of the plot of the natural log of remaining catalytic activity and time. Data are from three replicate experiments. Inhibition of CYP1A2 but not CYP1A1 by TCB is similar to results seen with rat liver CYP1As (Voorman and Aust, 1988).

• ↵5-a For CYP1A1, the catalytic assay was EROD and for CYP1A2, the catalytic assay was MROD.