HYDROXYSTEROID DEHYDROGENASES 



447 



spect to creatine phosphate (Nihei et al., 1961). However, ADP competes 

 with MgADP" in the reverse reaction. 



Since oxidative phosphorylation may in some ways be related to ATPase 

 activity and transphosphorylations, it is not out of place to discuss the ef- 

 fects of various inorganic phosphorus compounds on this process. The phos- 

 phorylation in a rat liver mitochondrial suspension oxidizing fumarate, and 

 with glucose and hexokinase to trap the phosphate, was studied by Thom- 

 son and Sato (1960) (Table 2-27). Some of the analogs investigated reduce 

 the P : ratio by depressing phosphate uptake more than oxygen uptake, 

 but the only compound that can be considered as a true uncoupler is thio- 

 phosphate. In such a complex system a number of sites for inhibition are 

 evident. It is known that anions can inhibit fumarase and it is possible that 

 other enzymes attacking dicarboxylates might be inhibited. Hexokinase is 

 inhibited at concentrations interfering with oxidative phosphorylation only 

 by triphosphate. Some of these compounds might deplete Mg++ but it was 

 shown that thiophosphate does not. It is not known if any of these sub- 

 stances can enter into the phosphorylative reaction but fail to form ATP. 

 Further study of thiophosphate would seem warranted by these preliminary 

 results. 



HYDROXYSTEROID DEHYDROGENASES 



The /?-hydroxysteroid dehydrogenase of Pseudomonas testosteroni cata- 

 lyzes the oxidations of 3/?- and 17/?-hydroxysteroids to their respective ke- 

 tones with NAD as acceptor. The oxidations of testosterone and 17/5-estra- 

 diol are competitively inhibited by 17cif-estradiol (Talalay and Dobson, 1953). 



H,C 



H,C 



OH 



Androstane 



Testosterone 



Androst-l-ene-3, 17-dione 



HO 



Estra-l, 3, 5-triene 



Estrone 



Progesterone 



