172 



CONTROL MECHANISMS IN CELLULAR PROCESSES 



obtain convincing evidence for the existence of separate proteins 

 catalyzing the oxidation of estradiol- 17yS by six different pyridine 

 nucleotides, or a variety of tranhydrogenase reactions. The most 

 purified preparations of the placental enzyme invariably reacted in 

 both dehydrogenase and transhydrogenase systems with the same 

 pyridine nucleotides that served as hydrogen donors or acceptors 

 in crude placental extracts. Table 6-1 shows that of ten acceptor 



TABLE 6-1 



Sp^cific'ty of Purified Placental Enzyme for 

 Pyridine Nucleotides and Analogues * 



Reactivity in Reactivity in 



Nucleotide Dehydrogenase Transhydrogenase 



Acceptor Reaction Reactions 



DPN + + 



TPN + 



DeaminoDPN f 



3-AcetylpyridineDPN + + 



3-Acetylpyridine deaminoDPN 



Pyridine-3-a!dehydeDPN + + 



Pyridine-3-aldehyde deaminoDPN 



TliionicotinamicieDPN + + 



Nicotinamide mononucleotide . 



Ribosyl nicotinamide 



** The reactions were studied at pH 7.4 under conditions similar to those described 

 by Talalay, Hurlock, and Williams-Ashman ( 1958 ) and by Talalay and Williams- 

 Ashman (1960). Estradiol-17/3 was used as substrate for the dehydrogenase reac- 

 tions. Hydrogen transfer from TPNH to acceptor nucleotides (transhydrogenase 

 reactions) was studied in the presence of 4 X 10 — ^ M estradiol-17/3 and continuously 

 generated TPNH at a final concentration of 3 X 10- ^ M. The concentration of the 

 acceptor nucleotides in both the dehydrogenase and transhydrogenase reactions was 

 4X 10-4 M. 



f DeaminoDPN is inert in both the dehydrogenase and transhydrogenase reactions 

 at pH 7.4 but will function as a hydrogen acceptor in both reactions at pH 8.5 

 (Talalay and Williams-Ashman, 1960). 



nucleotides tested with the purified enzyme, five were active and 

 five were inactive in the dehydrogenase system. These nucleotides 

 reacted in exactly the same way in the transhydrogenase reactions. 

 The experimental findings of the Chicago investigators ( Talalay, 

 Hurlock, and Williams- Asliman, 1958; Talalay and Williams- Ashman, 

 1960) are completely at variance with the report of Hagerman and 

 Villee (1959) that an enzyme catalyzing both the TPNH-DPN and 

 the DPNH-acetylpyridineDPN transhydrogenase reactions can be 

 separated from tivo pyridine nucleotide-linked estradiol dehydro- 



