The final step of aldosterone biosynthesis requires reducing power. It is not a dehydrogenation.

A mitochondrial preparation from adult duck adrenal gland was used to study the mechanism (dehydrogenation or other) of the last step of aldosterone biosynthesis (18-oxidation) by incubation of tritiated 18-hydroxycorticosterone. Results show that the role of citric acid cycle metabolites is to provide reducing power. When reducing power is provided by malate, which yields NADH or NADPH directly, the reoxidation of reduced coenzymes in the oxidative phosphorylation chain is not necessary. In the presence of succinate, the oxidative phosphorylation chain is required, but only to provide ATP. Stimulation of the reaction by low concentrations of KCN in the presence of malate shows that the reducing power is not used in the oxidative phosphorylation chain. These data suggest that the reaction is not a dehydrogenation and that the reducing power is used in a pathway competing with the respiratory chain, most probably a hydroxylating pathway, in mitochondria.