Steroid aromatization by a small particle fraction from porcine ovaries.

Testosterone, 4-androstene-3,17-dione, 19-hydroxy-4-androstene-3,17-dione, 4alpha-5-oxido-5alpha-androstane-3,17-dione and 4beta-5-oxido-5beta-androstane-3,17-dione were compared as substrates for aromatization by the small particle fraction from sow ovaries. Relative conversion rates were: 19-hydroxy-4-androstene-3,17-dione:4-androstene-3,17-dione: testosterone: 4alpha-5-oxido-5alpha- and 4beta-5-oxido-5beta-androstane-3,17-dione; 100:32:20:congruent to O. Apparent Michaelis constants were 4.4 muM for 4-androstene-3,17-dione and 12 muM for testosterone. Maximum velocities were 0.20 pmoles/mg protein per min for androstenedione [1] and 0.16 for testosterone. The substrate preferences of the aromatizing system found in ovary are similar to those of the enzyme found in placenta.