Corticosteroid side-chain isomerase in mouse organs: kinetic and immunologic studies

We have investigated the distribution of corticosteroid side-chain (CSC) isomerase in the tissues of mice using as criteria its enzyme activity and immunoreactivity with monospecific polyclonal antibodies generated in rabbits. CSC isomerase was present in all organs examined. The liver and kidney contained the highest activity. The strain-dependent differences that we had previously reported for liver (i.e., BALB/c greater than C57BL/6) extended to the other organs, including the kidney, brain, heart, muscle, pancreas, testis, thymus, and lung. Western blot analysis showed a single antigen, identical in all tissues, corresponding in mobility to purified CSC isomerase. The intensities of the bands were generally proportional to enzyme activities. Titration of homogeneous enzyme with the IgG fraction of antiserum (unfractionated serum had some CSC isomerase activity) caused an increase in activity, followed by rapid inactivation after the addition of more antiserum. The broad distribution of CSC isomerase suggests that the ketol-aldol interconversion of the CSC may play a role other than, or in addition to, initiating metabolic inactivation of corticosteroids.