STRUCTURE OF PHOTOS YNTHE TIC SULFUR BACTERIA 77 



PO4 RELEASE 



5 10 



TIME 



15 20 25 

 IN MINUTES 



35 



Fig. 4. Phosphorus uptake by a particulate fraction from 

 Chlorobium. The fraction consisting of pigmented particles 

 was incubated in light and dark in Warburg vessels contain- 

 ing 0.8 ml extract; 10 //moles MgCl2; lO^umoles Kh2P04; 

 100 yUmoles Tris pH 7.0; 7.5 yUmoles ADP; 0.5 ml Hexokinase 

 (Sigma), and water to a total vol. of 2.5 ml. 0.5 ml of TCA 

 (10%) was added to stop the reaction and the precipitate re- 

 moved by centrifugation. Rates of phosphate uptake are ex- 

 pressed as/imolesorthophosphateesterifiedAr/mg chloro- 

 phyll. 



recently shown that bacteriochlorophyll is also associated with the 

 particle from Chlorobium and have suggested that Chlorobium chloro- 

 phyll may act as an accessory pigment to the photochemically active 

 bacteriochlorophyll. 



It is only recently that we have been able to show that the small 

 particle is indeed an active photochemical system. During experi- 

 ments designed to measure light-dependent phosphate uptake, inorganic 

 phosphate was always released into the medium, making measurements 

 of photophosphorylation difficult. It has recently been shown by Hughes 

 et al. (11) that Chlorobium thiosulfatophilum accumulates large amounts 



