Interaction of phenols with δ9 terminal desaturase and other cyanide-sensitive factors in chicken liver microsomes

Abstract

p-Cresol stimulates the oxidation of reduced cytochrome b 5 in chick embryo liver microsomes, which lack stearoyl-CoA desaturase activity, as well as in hepatic microsomes from neonatal chicks and fasted-refed adult chickens, both of which have greatly increased stearoyl-CoA desaturase activity. The K m value of p-cresol for the interaction in chick embryo microsomes is 2–4 mM, whereas that in adult liver microsomes is only 6 μM; the V value for p-cresol in the adult is 2-fold higher than that in chick embryo. During neonatal development the shift in the K m value of p-cresol from high to low occurs concomitantly with the formation of stearoyl-CoA desaturase activity in newly hatched chicks. Antibodies to Δ 9 desaturase completely inhibit stearoyl-CoA desaturation but inhibit only 50% of the p-cresol-stimulated oxidation of cytochrome b 5 in hepatic microsomes from adult chickens, indicating that the p-cresol effect in adult chicken microsomes is partly mediated by Δ 9 terminal desaturase. In chick embryo liver microsomes antibodies to Δ 9 desaturase do not inhibit p-cresol-dependent oxidation of cytochrome b 5. In chick embryo and adult microsomes p-cresol is converted to a more polar product whose formation is dependent on NADH, microsomes and is inhibited by KCN. The results support the conclusion that p-cresol interacts with several microsomal cyanide-sensitive factors including Δ 9 terminal desaturase. On the basis of cyanide sensitivity of the interaction of various phenols with hepatic microsomes, phenols can be classified into three groups; cyanide-sensitive phenols (e.g., p-cresol) which interact exclusively with cyanide-sensitive factors; cyanide-insensitive phenols (e.g., p-aminophenol, hydroquinone and catechol) which interact directly with cytochrome b 5 and partly cyanide-sensitive phenols (e.g., phenol) which interact with both cytochrome b 5 and cyanide-sensitive factors.