FIGURE 4.

The effects of 4-HPR, 4-HPR metabolites, and C₈-CPPC on desaturase activity in vitro. A, the effects of increasing concentrations of 4-HPR and 4-HPR metabolites on DES activity in rat liver microsomes. In these experiments, [C₈-dhCer] was 0.25 K_m, and the inhibitor concentrations were between 1 and 7.5 μm. The values represent the mean ± S.D. of two independent experiments performed in triplicate. B, the effects of increasing concentrations of C₈-CPPC on DES activity in rat liver microsomes. In these experiments, [C₈-dhCer] was 0.25 K_m, and C₈-CPPC concentrations were 0.5, 0.75, and 1 μm. The values represent the mean ± S.D. of two independent experiments performed in triplicate. C, the effects of increasing concentrations of 4-oxo-HPR on DES activity in rat liver microsomes. DES activity was measured using a fixed amount of substrate (2 nm labeled and 500 nm unlabeled substrate) and increasing concentrations of 4-oxo-HPR (0, 1, 2.5, 5, 10, 25, and 50 μm). The values represent the mean ± S.D. of two independent experiments performed in triplicate, D, the effects of increasing amounts of substrate on 4-oxo-HPR inhibition of DES activity in rat liver microsomes. DES activity was measured using a fixed concentration of 4-oxo-HPR (10 μm) and increasing amounts of substrate (from 0.25 to 3 K_m). The values represent % inhibition as compared with controls and the mean ± S.D. of two independent experiments performed in triplicate. E, Lineweaver-Burke plot for K_i demonstrating DES activity with increasing concentrations of 4-oxo-HPR. For these experiments, the [substrate] was fixed and ranged from 0.25, 0.5, 1, 2, to 3 K_m, and the [4-oxo-HPR] used ranged from 0, 1, 2.5, 5, 10, 25, and 50 μm. Values represent the mean ± S.D. of five independent experiments performed twice in triplicate. F, table of IC₅₀ values for 4-HPR, 4-oxo-4HPR, and C₈-CPPC. Values represent the mean ± S.D. of three independent experiments performed in triplicate.