Reversibility of Steroid Δ-Isomerase

When large quantities of androst-4-ene-3,17-dione were incubated with reduced diphosphopyridine nucleotide and an acetone powder of sheep adrenal microsomes, 3β-hydroxyandrost-4-en-17-one and its Δ5 isomer were isolated and crystallized as their benzoates. The melting points and infrared spectra were in agreement with those of the corresponding standards. A similar incubation of unlabeled androst-5-ene-3,17-dione produced 3β-hydroxyandrost-5-en-17-one in good yield. Since incubation of 3β-hydroxyandrost-4-en-17-one-3α-3H yielded nonradioactive 3β-hydroxyandrost-5-en-17-one and androst-4-ene-3,17-dione, it was concluded that the isomerase did not act on the allylic alcohol. 3β-Hydroxyandrost-4-en-17-one-3α-3H and -3α-H were incubated simultaneously in the presence of diphosphopyridine nucleotide and an acetone powder of sheep adrenal microsomes for varying times. There was no measurable difference in the rates of oxidation of these two allylic alcohols.