title: Regulation of 18-hydroxycorticosterone formation in bovine adrenocortical mitochondria.
abstract: The conversion of deoxycorticosterone to 18-hydroxycorticosterone was examined by using sonicated mitochondrial suspension of bovine adrenocortex. The KM's of deoxycorticosterone for the 11 beta- and 18-hydroxylations were in the same range (1 microM), while the turnover number for the 11 beta-hydroxylation (50 nmol/min/nmol cytochrome P-450) was 6 times as great as that for the 18-hydroxylation (7.3). The KM and turnover number for the 18-hydroxylation of corticosterone were 6 microM and 0.4, respectively. Those for the 11 beta-hydroxylation of 18-hydroxy-11-deoxycorticosterone were 120 microM and 5. When products were analysed in the incubation of deoxycorticosterone with the mitochondrial suspension containing a larger amount of cytochrome P-450, the formation of 18-hydroxycorticosterone was observed in addition to the formation of corticosterone and 18-hydroxy-11-deoxycorticosterone. The kinetic interrelation between the two pathways was further examined together with consideration of the cytochrome P-450-linked hydroxylation system. The result suggests that the pathway via 18-hydroxy-11-deoxycorticosterone substantially participates in the formation of 18-hydroxycorticosterone from deoxycorticosterone. The perturbation of this network by an artificial means, such as the addition of Triton X-100, revealed that the detergent (0.02%) facilitated the production of 18-hydroxycorticosterone from deoxycorticosterone, regardless of its inhibitory effect on the production of corticosterone and 18-hydroxy-11-deoxycorticosterone from deoxycorticosterone. These studies provide an important insight into the regulation mechanism of 18-hydroxycorticosterone formation from the precursors on the mitochondrial level.
mesh_terms: D015062:11-Hydroxycorticosteroids / Q000096:biosynthesis; D015065:17-Hydroxycorticosteroids / Q000096:biosynthesis*; D015069:18-Hydroxycorticosterone / Q000096:biosynthesis; D000311:Adrenal Glands / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D003345:Corticosterone / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003900:Desoxycorticosterone / Q000378:metabolism; D006900:Hydroxylation; D008928:Mitochondria / Q000378:metabolism; D011092:Polyethylene Glycols / Q000494:pharmacology
chemical_list: D015062:11-Hydroxycorticosteroids; D015065:17-Hydroxycorticosteroids; D011092:Polyethylene Glycols; D003900:Desoxycorticosterone; D015069:18-Hydroxycorticosterone; D003577:Cytochrome P-450 Enzyme System; D003345:Corticosterone