Abstract
Two strains (No. 144 and No. 146) of rat intestinal anaerobic bacteria, phenotypically similar to Eubacterium lentum, were isolated and found capable of 16α-dehydrating corticoids. The initial step in the 16α-dehydration of 16α-hydroxyprogesterone was dehydration at the C-16 and C-17 position with the accumulation of 16-dehydroprogesterone. This step required the side chain at C-17. In bacterial cultures the 16-dehydroprogesterone was then slowly reduced to iso-progesterone. 16α-Hydroxypregnanolone was also converted to iso-pregnanolone by these bacteria. 16α-Dehydratase was easily demonstrated in cell fractions of strain No. 144 incubated either aerobically or anaerobically. The same extracts did not convert 16-dehydroprogesterone to iso-progesterone under similar assay conditions. 16α-Dehydration occurred at all substrate concentrations tested (20 to 200 μg/ml) provided the pH of the growth medium was between 6 and 8 and the Eh below -130mV. Strain No. 146 had both 16α-dehydration and 21-dehydroxylation activities. The two enzymes functioned independently. A role for intestinal bacteria in the biotransformation of biliary 16α-hydroxylated steroids and subsequent excretion in the urine is proposed.
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