Δ 5-3-Ketosteroid isomerase activities in guinea-pig adrenal glands: The role of copper ions

Abstract

1. (1) Androst-5-ene-3,17-dione isomerase, pregn-5-ene-3,20-dione isomerase and 17α-hydroxypregn-5-ene-3,20-dione isomerase activities were found in the initial extract of guinea-pig adrenal glands and in its particulate cell fraction. The soluble cell fraction showed no activity and the particulate fraction contained not more than one third of the activity present in the initial extract. Combining the soluble with the particulate fraction augmented the isomerization rate considerably. 2. (2) Addition of copper ions (Cu 2+, Cu +) to the soluble fraction activated the three isomerases in this cell fraction. The effect appears to specifically require copper ions. 3. (3) Both augmentation of the isomerization rate obtained with the combined soluble and particulate fractions and activation of the isomerizing capacity in the soluble fraction require a non-dialyzable factor besides copper ions. 4. (4) It appears that the two observations reflect the action of the same factor and that the catalytically active, non-dialyzable, thermolabile, and copper-sensitive factor in the soluble fraction is an enzyme protein lacking copper ions at the proper concentration for its activity. 5. (5) It is further suggested that the particulate fraction contains structurally bound ionic copper, thus providing ionic copper for the activity of the enzyme protein in the soluble fraction, when soluble and particulate fractions are combined. 6. (6) Finally, it appears that two isomerizing systems exist side by side, one associated with the cell particles, the other detected only in presence of the soluble fraction and copper ions.