Cofactor dependency of soluble 3 alpha-hydroxysteroid oxidoreductases in rat testis, prostate, and epididymis

The present paper demonstrates the presence of at least two 3-hydroxysteroid oxidoreductases (3-HSO) in rat testis, prostate, and epididymis cytosol preparations. The enzymes were either NADH or NDAPH dependent. Further investigation by Sephadex G-200 chromatogrphy revealed the presence of enzyme activities in the void volume (peak 1) and also eluting close to the methyl-carbonic anhydrase standard (mol wt, 34,000; peak 2). Enzyme activity in peak 1 was predominantly stimulated by NADH and that in peak 2 was stimulated mainly by NADPH. Both 3 alpha- and 3 beta-HSO activities were observed in testicular eluates from 1; 3 beta-Adiol accounted for up to 50% of the 5 alpha-androstanediols formed. In peak 2,3 alpha-HSO constituted more than 90% of the enzyme activity. In contrast, the prostatic and epididymal eluates revealed only 3 alpha-HSO activity; 3 beta-Adiol constituted less than 5% of the 5 alpha-androstanediols formed in either peak 1 or 2. The apparent Km values for enzyme activation reveal differences in sensitivity to cofactors for enzymes in peaks 1 and 2 and also among testis, epididymis, and prostate. NADH caused a very similar activation of enzyme activity in peak 1 or the prostate and epididymis (Km 50-100 micro M), whereas the enzyme in the testis was activated by much lower cofactor concentration (Km approximately 5 microM). It is possible that this enzyme activity may represent microsomal contamination. The enzyme activity in peak 2 revealed very similar sensitivity to NADPH in all three organs (Km, 0.6-1.7 microM), confirming previous studies from our laboratory that the soluble. NADPH-dependent enzymes in all three tissues are very similar, if not identical.