790 15. EFFECTS OF VARIOUS FACTORS ON INHIBITION 



the effect of an inhibitor on (B) will depend on the initial \'\IV2 ratio, 

 which can l)e modified by the temi)erature. 



Examination of an homologous series of carbamates for their effects on 

 the luminescence of PJiotobacterimn pho.sphoreuiH demonstrated that the 

 temperature relationships changed as the alkyl chain length increased 

 (Johnson et al., 1951). While methyl carl)amate and ethyl carbamate (ure- 

 thane) shift the T^^^^, downward. >?-propyl carbamate and >*-hexyl carbamate 

 shift it upward, indicating that the inhibiting actions are different in some 

 way. On the enzyme-denaturation hypothesis one must assume then that 

 the higher homologs do not favor denaturation; on the multienzyme basis 

 one must assume that the higher homologs act predominantly on a different 

 pathway. The effects of high ])ressure on the inhibitions also support a 

 different type of action. It may also be pointed out that ethanol exerts 

 effects similar to urethane in that the T,^^,, is shifted to lower temperatures 

 (Johnson et al., 1945) and has been shown to inhibit luciferase at high con- 

 centrations (it requires about 1 M to inhibit 50%) (Cliase. 1952). A more 

 detailed summary of the study of the inhibition of luminescence and its 

 interpretation may be found in "The Kinetic Basis of Molecular Biology" 

 (Johnson et al, 1954). 



(D) Inhibition of Bliizobium respiration by uretJiane. The results obtained 

 by Koffier et al. (1947) for the inhibition of respiration are very similar to 

 those just discussed for luminescence. The inhibition by urethane increases 

 w^ith the temperature; for example, with 300 mM urethane, the following 

 inhibitions were observed. There is no marked effect on the T^^,^ but it 



Temperature Inhibition (t) 



18° 

 310 



0.36 

 0.56 



400 () s4 



is shifted slightly to lower temperatures. These results w^ere interpreted in 

 terms of an equilibrium between native and denatured enzymes and the 

 similarity between the inhibitions on respiration and methylene blue 

 reduction pointed to the dehydrogenases as l)eing the enzymes involved. 

 Incidentally, these results make it likely that urethane in acting on the 

 ATP-forming ])atliways in addition to luciferase in the studies of bac- 

 terial luminescence. 



(E) Retardatio)} of cell division by urethane. The cleavage of Arbacia eggs 

 is retarded by uretlianes and it has been sliown by Cornman (1950, 1957) 

 that the effectiveness is least at 200-21°. The concentrations required for 



