56 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



Experiment 2. The effect of dinitrophenol (DNP) (6 x 10-5 M) is 

 similar to that of dicoumarol (Fig. 2). When lower concentrations of 

 either dicoumarol or DNP were used bacteriochlorophyll synthesis 

 was inhibited but to a lesser degree (Table 1), 



Experiment 3. Amytal at a concentration of 1,6 x 10-3 M inhibits 

 bacteriochlorophyll synthesis to a lesser extent than growth (Fig. 3); 

 consequently, the specific bacteriochlorophyll content increases. This 

 is in marked contrast to the results with DNP and dicoumarol, 



TABLE 1 



Comparison of the effects of certain inhibitors on growth and 

 bacteriochlorophyll synthesis. 



T , ., .. ,, , ., Relative Relative bacterio- 



Inhibitor Molaritv ^, ^ , , , ,, ^ ^ 



^ growth rate chlorophyll content 



In order to avoid the effects of self-shading, the bacteriochlorophyll content 

 was determined in each case when the bacteriochlorophyll concentration was 

 Afig/ml. 



Experiment 4. Cohen- Bazire and Kunisawa (4) have reported that 

 the specific bacteriochlorophyll content is reduced in cultures grown 

 at a low temperature. Fig. 4a shows the results of an experiment in 

 which a culture was subjected to a sudden decrease in temperature. 

 Bacteriochlorophyll formation is inhibited, but not completely as it is 

 after addition of DNP or dicoumarol. Essentially the same result is 

 obtained when growth is inhibited by 5-methyltryptophan (Fig. 4b). 



Fig. 5 shows the differential rate of bacteriochlorophyll synthesis 

 in the presence of amytal and of 5-methyl-tryptophan. In Table 1 are 

 shown the relative growth rates and bacteriochlorophyll contents ob- 

 tained with inhibitors. 



