Retroconversion of Estrogens into Androgens by Bacteria via A Cobalamin-Mediated Methylation

Sex steroids, namely androgens and estrogens, modulate physiology, development, and reproduction of animals. Biosynthesis of C₁₈ estrogens proceeds through the removal of the C-19 angular methyl group from C₁₉ androgens, resulting in the formation of an aromatic A-ring. This aromatization proceeds through the oxidative bond cleavage between steroidal C-10 and C-19, which is catalyzed by an aromatase at the cost of NADPH and O₂. The reverse reaction (from estrogens to androgens) is thermodynamically challenging and has not been reported in any organisms.