TRANSHYDROGENASE REACTIONS AND ESTROGENS 181 



dine nucleotide transhydrogenase facilitates the capture of energy 

 from the oxidation of TPNH by promoting the transfer of hydrogen 

 to DPN and thus permitting the synthesis of adenosine triphos- 

 phate (Kaplan, Swartz, Freeh, and Ciotti, 1956; Vignais and Vignais, 

 1S57 ) . But whether estradiol-dependent transhydrogenations of the 

 type catalvzed bv the placental enzyme are of regulatory signifi- 

 cance (Talalay and Williams-Ashman, 1958) is problematical. Villee, 

 Hagerman, and Joel ( 1960 ) have shown that the direct addition of 

 estradiol-17/3 to placental slices increases the incorporation of radio- 

 active acetate and glycine into protein, lipide, and the adenine and 

 guanine of nucleic acids. Hosoya, Hagerman, and Villee ( 1960) ob- 

 served a direct stimulation of fatty acid synthesis by estradiol-17/3 

 in a cell-free placental extract. However, insufficient evidence is 

 available to relate these interesting effects of estradiol-17yS in vitro 

 to the stimulator)- influence of this estrogen upon the transfer of 

 h\ drogen from TPNH to DPN. In placenta, the rates of this trans- 

 Indrogenation catahzed by the soluble, estradiol-stimulable enzyme 

 are considerably slower than those catalvzed bv the mitochondrial 

 transhydrogenase, which is insensitive to estradiol-17^ (Villee, 

 Hagerman, and Joel, 1960 ) . 



A major objection to the hypothesis that transhydrogenations cat- 

 alyzed by the soluble placental enzyme are related to the mecha- 

 nism of estrogen action is the fact that this enzyme is not stimulated 

 by many synthetic, non-steroidal estrogens (Villee, 1957; Talalay and 

 Williams-Ashman, 1958 ) . Thus, substances such as diethylstilbestrol, 

 hexestrol, substituted triphenvlethvlenes, etc., do not mediate the 

 TPNH-DPN reaction, and in substrate amounts they do not oxidize 

 or reduce pyridine nucleotides, in the presence of the placental en- 

 zyme. This is not altogether surprising, as these compounds are 

 devoid of either secondary alcohol or ketone groups and cannot un- 

 dergo oxidoreduction in the same way as estradiol-17^. Like many 

 other phenols, both natural and artificial 'phenolic estrogens may 

 promote hydrogen transport in catalytic concentrations in a number 

 of oxidations catalyzed bv phenolases and peroxidases (Williams- 

 Ashman, Cassman, and Klavins, 1959; Klebanofi^, 1959; Temple, Hol- 

 lander, Hollander, and Stephens, 1960; Talalay and Williams-Ash- 

 man, 1960). But only those estrogens possessing at least one free 

 li)droxyl group transport hydrogen in these model reactions, and 

 the ability of various phenols to stimulate these metalloprotein cata- 

 lyzed oxidations bears no relationship to their estrogenic activity. 



