182 CONTROL MECHANISMS IN CELLULAR PROCESSES 



Furthermore, these reactions are not catalyzed by the purified placen- 

 tal enzyme. There is no evidence that synthetic estrogens such as 

 hexestrol and diethvlstilbestrol are transformed metabolicallv into 

 steroid-like substances (cf. Talalay and Williams- Ashman, 1960), 

 and it would seem improbable that the biochemical mechanism ( s ) 

 responsible for the biological action of synthetic non-steroidal estro- 

 gens is completely different from that involved in the action of natu- 

 ral hormones such as estradiol- 17^. 



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