280 



INTRACELLULAR LUMINESCENCE 



linear, when plotted in the manner illustrated in Fig. 10, the slope 

 of the line indicating the ratio of drug to enzyme molecules in the 

 equilibrium established. In Fig. 10, it is evident that the relationship 

 is not linear throughout a wide range of drug concentrations, for the 

 slope increases at the higher concentrations. Moreover, the numerical 



2.0 



1.0 



Jo.o 



o 



10 



Luminescence 



P. phosphoreum 



pH7 



1 



— Slope = s = 



/ 



/ 



/ 



yC. 



/ 



/ 



y 



^j^ Slope = 2.8 

 Slope = 1.0 



o--'*'-s = 13 



Yeast oxygen 

 consumption 



2.0 L 



2.5 



00 



10 15 



log jg molar concentration urethan 



Fig. 10. Relation between concentration of urethan (abscissa) and amount of 

 inhibition (ordinate) of luminescence in P. phosphoreum at 5°, 20°, and 

 30° C, respectively. The symbol Ti for inhibition represents [(L/Iw) — 1], 

 where /<■ is the intensity of luminescence in a control suspension of bacteria, 

 and /u is the intensity in a corresponding suspension containing a given 

 concentration of the drug. (Data of Johnson et ah, 1945.) The broken line 

 repres*ents data replotted from Fisher and Stearn (1942) concerning the 

 urethan inhibition of oxygen consumption in yeast. (From Johnson, Eyring, 

 and Polissar, 1954, courtesy of John Wiley & Sons.) 



values of the slopes are not integers, and they change with tempera- 

 ture. They also change with pressure. It follows that more than a 

 single equilibrium is involved in the total effect, and the measured 

 slopes give only the average ratios of the combining molecules. 



Figure 10 indicates a similarity in the action of urethan on bacterial 

 luminescence and on yeast respiration. The data on the latter process 

 were interpreted to mean that two different enzyme systems are af- 



