38o 



DANIEL I. ARNON 



20 40 



minutes 



Fig. 22. Effect of succinate on photofixation of nitrogen gas by Chromatium 

 cells. Experimental conditions as described in Fig. 21, except that thiosulphate and 

 oxaloacetate were omitted. 20 /imoles of succinate were added as indicated (Losada, 

 Nozaki, Tagawa, and Arnon [155, 154]). 



sulphate was the electron donor (Table IX). These results suggest that 

 ammonia or Ng did not inhibit the flow of electrons that are required for 

 CO2 assimilation (by way of DPNH., or TPNHg). At high light intensity, 

 when the electron flux is large enough to cope with the requirements of 



Fig. 23. Effect of ammonia on photofixation of nitrogen gas with thiosulphate 

 by Chromatium cells. Experimental conditions were the same as described for Fig. 

 21 except that 30 //.moles of NH4CI were added as indicated (Losada, Nozaki, 

 Tagawa, and Arnon [155, 154]). The addition of ammonia to, or the omission of 

 thiosulphate and oxalacetate from, the complete system prevents nitrogen fixation. 



