PHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 381 



TABLE IX 



Effect of Nitrogen (Jas and Ammonia on CO^ Fixation by Illuminated 

 Chromatium Cells with Thiosulphate as Electron Donor 



(Losada, Xozaki, and Arnon [136]) 



Total i^CO, fixed 

 Treatment counts/min. 



(thousands) 



Argon 524 



Argon + thiosulphate 2190 



No + thiosulphate 2238 



Argon + thiosulphate + NH4CI 2436 



The reaction mixture contained in a total volume of 3 ml. : 50 mg. of washed 

 cells, suspended in 2-3 ml. of a modified nutrient solution from which nitrogen 

 compounds were omitted, and the following in micromoles : tris buffer, pH 

 7'5> 15°; thiosulphate, 20; and sodium bicarbonate labelled with ^^C, i -o. 30 

 ^tmoles of NH4CI were added as indicated. Gas phase, argon or No as indicated. 

 The reaction was carried out at 30 . 



both X.> fixation and CO^ assimilation, both processes can occur 

 simultaneously. 



CELL-FREE NITROGEN FIXATION 



In preliminary experiments, when cell-free Chromatium preparations 

 were supplied in the dark with a mixture of hydrogen and nitrogen gas, 



TABLE X 



No Fix.^TioN in the Dark uy Cell-Free Extracts of Chromatium Supplied 



WITH Hydrogen Gas 



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



Cjas uptake, mm. pressure change 



Cofactors added q^^ phase q^^ ^^^^^ 



Ho 50% Ho + 50"., N., 



None o —11 



DPN - 22 - 62 



The reaction mixture contained, in a final volume of 3 ml. : cell-free extract 

 containing 0-27 mg. bacteriochlorophyll, and the following in niicromoles : tris 

 buflFer, pH 7-5, 150; MgCla, 5; and, where indicated, DPN, 0-5 (added jointly 

 with benzyl viologen, 0-2). The gas phase was in one case hydrogen gas and in 

 the other a mixture of nitrogen and hydrogen in equal volume. KOH was present 

 in the centre wells of the manometer vessels. The reaction was run for 45 min. 

 at 25° in the dark. 



