A NOTE ON THE EFFECT OF INHIBITORS OF 

 ELECTRON TRANSPORT AND PHOSPHORY- 

 LATION ON PHOTOPIGMENT SYNTHESIS 

 m RHODOPSEUDOMONAS SPHEROIDES 



W. R. SISTROM 



The Biological Laboratories , Harvard University, 



and The Department of Biology, 



University of Oregon 



INTRODUCTION 



The general features of the control of photopigment synthesis in 

 the photosynthetic bacteria are well known (1,2). The hypothesis orig- 

 inally proposed (1) to account for the changes in the bacteriochlorophyll 

 and carotenoid pigment contents of cells grown at different light in- 

 tensities or oxygen tensions is adequate to a first approximation at 

 least. It does not, however, account satisfactorily for all the kinetic 

 observations (2), The hypothesis assumed that pigment synthesis is 

 controlled by the ratio of the oxidized to the reduced form of an electron 

 carrier. When the carrier becomes oxidized, for example by a sudden 

 increase in light intensity, pigment synthesis is inhibited; conversely, 

 when the carrier is reduced, pigment synthesis is accelerated. 



More recent experiments have shown that at constant light intensity 

 the bacteriochlorophyll content of a culture depends directly upon its 

 growth rate. For example, when Rhodopseudomonas spheroides is 

 maintained in a chemostat the pigment content of the cells depends 

 upon the dilution rate. If it is assumed that the rate of reduction of the 

 electron carrier which controls pigment synthesis is proportional to 

 the growth rate, then our original hypothesis can account for these re- 

 sults also. 



It seemed possible that the site of control could be determined by 

 studying the effect of inhibitors of electron transport and phosphoryla- 

 tion on bacteriochlorophyll synthesis. This paper describes in a pre- 

 liminary way some experiments along these lines. The results indicate 

 that this will be a fruitful approach and suggest that pigment synthesis 

 is controlled by the ratio of reduced to oxidized DPN, 



53 



