PHOTOSYNTHETIC PHOSPHORYLATION" AND THE ENERGY CONVERSION PROCESS 379 



Fig. 21. Effect of thiosulphate and oxaloacetate on photofixation of nitrogen 

 gas by Chromatiimi cells. The reaction mixture included in a final volume of 2-9 

 ml., 01 g. of washed cells, suspended in a modified nutrient solution, pH 72 

 (from which nitrogen compounds were omitted). 20 /^moles each of thiosulphate 

 and oxaloacetate were added as indicated, o • i ml. of 20",, KOH was placed in the 

 centre wells of the Warburg manometer flasks. The reaction was run at 30 . Gas 

 phase, nitrogen. Illumination 50 000 Lux (Losada, Xozaki, Tagawa, and Arnon 

 [155, 154]). , 



acceptor. Succinate ser\ed both as electron donor and as source of a 

 carbon skeleton that is needed for accepting an amino group. 



As shown in Fig. 23, photofixation of X., with thiosulphate was 

 inhibited by ammonia (cf. [149]). Howe\ er, neither ammonia nor nitrogen 

 gas inhibited COo fixation by illuminated Chronuitium cells when thio- 



TAHLK VIII 



Effect of Light and Electron Donors on Fixation of Molecular Nitrogen 



BY Chromatiiim Cells 



(Losada, Xozaki, Tagawa, and Arnon [155, 154]) 



Treatment 



Atom percent ^^X 

 excess 



Dark, succinate 



Dark, thiosulphate 



Light 



Light, succinate 



Light, thiosulphate 



oxaloacetate 



oxaloacetate 



0-004 



-003 

 0-288 



1 -049 

 1-467 



40 fimoles each of thiosulphate, oxaloacetate and succinate were added as 

 indicated. Other experimental conditions as in Fig. 21, except that no KOH 

 was included, and the gas atmosphere was 90*^0 argon and 10",, X,, containing 

 30 atom percent excess ^*X. Reaction time was 2 hr. 



