60 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



of the cells, the supply of photooxidant will accordingly fall and the 

 electron carriers will return to their initial level of reduction and 

 bacteriochlorophyll synthesis will recommence, 



Amytal is reported to be a poor inhibitor of cyclic photophosphory- 

 lation in Rko do spirillum rubrum chromatophores (5); however, amytal 

 is known to block the oxidation of DPNH by flavoprotein in mitochondria 

 (6), It therefore seems reasonable to ascribe both the inhibition of 

 growth and the stimulation of the differential rate of bacteriochlorophyll 

 synthesis by amytal to a decrease in the rate of DPNH oxidation. In 

 other words, the electron carrier which controls pigment synthesis is 

 DPN. Preliminary results indicate that 2- w-nonyl- hydroxy quinoline-N- 

 oxide and SN5949 have the same effect on bacteriochlorophyll synthesis 

 as amytal. 



Atebrin inhibits photophosphorylation in /?.rM&rMW chromatophores 

 (7) and DPNH oxidation in mitochondria (8), In each case it is likely 

 that the inhibition is on a flavoprotein. It would be expected that atebrin 

 should have the same effect as amytal. As can be seen from Table 1, 

 this is not the case: atebrin inhibits growth and reduces the specific 

 bacteriochlorophyll content. However, it should be noted that the pig- 

 ment content is reduced by only 15%, although growth is inhibited by 

 almost 50%. This is in contrast to the results with DNP, dicoumarol 

 and 5-methyl-tryptophan. It is possible that atebrin inhibits growth not 

 only by interfering with oxidation of DPNH but also in some other 

 fashion unrelated to electron transport. The small reduction in specific 

 bacteriochlorophyll content which is observed may represent the net 

 result of these contrary tendencies. 



ACKNOWL EDGME NTS 



This work has been supported by grants from the National Science Foundation 

 and the National Institutes of Health. 



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2. Sistrom, W. R.,J. Gen. Microbiol., 28,607 (1962). 



3. Sistrom, W. R., J. Gen. Microbiol., 22, 778 (1960). 



4. Cohen-Bazire, G., and R. Kunisawa, personal communication. 



5. Baltscheffsky, H., and M. Baltscheffsky, Acta Chem. Scand., 11,2^1 (1960). 



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