Oxidation and reduction of the C-11 position of corticosterone and 11-dehydrocorticosterone by mouse liver fractions in vitro

Corticosterone and 20α dihydrocorticosterone have been found in the liver and blood of mice injected intravenously with C-11-dehydrocorticosterone. Within a few minutes after injection the latter is no longer detectable in the blood and liver, (1). The enzyme responsible for the reduction of the C-11 keto group has been isolated in the microsomal fraction of mouse liver homogenate. This fraction was precipitated by ultracentrifugation at 100,000 x G of the supernatant after centrifugation at 6,000 x G. NADPH₂ was established as the coenzyme required although limited activity could be demonstrated with NAD₂. The reaction can be reversed by use of NADP. Certain kinetic properties of the reaction have been investigated. The reaction velocity is proportional to enzyme concentration and linear with time over the period studied. For the reduction reaction with 11-dehydrocorticosterone as substrate Km = 1.8 x 10⁻⁵ and Vmax = 1.6 x 10⁻⁴ μmoles/ml/min. For the dehydrogenation reaction with corticosterone as substrate Km = 1.7 x 10⁻⁴ and Vmax = 2.7 x 10⁻³ μmoles/ml/min.Medicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat