450 



2. ANALOGS OF ENZYME REACTION COMPONENTS 



ever, inactive, indicating very specific attachment to the enzyme. The K^ 

 for 17/5-hydroxyandrosta-l,4-diene-3-one is 0.146 mM when the substrate 

 is cortisone (iiC,„ = 0.14 xaM), and the other inhibitors presumably have 

 similar values for K^. It may also be noted that 6of- and 6y5-methyl-ll-keto- 

 progesterone are inhibitors. 



The normal roles of these enzymes in bacteria or mammals are not as 

 yet well understood, although the steroid dehydrogenases in Pseudomonas 

 enable this organism to grow with the appropriate steroids as the sole 

 source of carbon. There are many other enzymes involved in steroid syn- 

 thesis and catabolism which have not been studied with respect to analog 

 inhibition. When such studies are made it may well be found that this is 

 an important regulating mechanism in controlling the levels of the steroid 

 hormones. 



NITRITE AND SULFITE METABOLISM 



Nitrobacter is a soil autotroph that can obtain its energy from the oxida- 

 tion of nitrite to nitrate. Chlorate at low concentrations (0.01-0.1 mM) 

 inhibits growth without affecting nitrite oxidation, whereas at higher con- 

 centrations (above 1 mM) nitrite oxidation is progressively depressed (Lees 

 and Simpson, 1955). The inhibition is completely reversible and it was pos- 

 tulated that chlorate combines with a nitrite-oxidizing enzyme at a stage 

 when it is bound to nitrate; however, the inhibition seems to be unrelated 

 to the concentrations of either nitrite or nitrate, and is not reversed by 

 increasing the nitrite concentration (Lees and Simpson, 1957). It was then 

 postulated that chlorate does not inhibit directly but is first converted to 

 some substance, perhaps chlorite, which inhibits rapidly and irreversibly. 



Nitrite 



o 



N=C=0 

 'N— C=0^ 

 '^N=C— O' 



Cyanate 



Related anions do not inhibit comparably with chlorate (see tabulation, 

 where nitrite is 8mM), but cyanate is apparently even more inhibitory 



