PHOSPHORYLATION IN Cfilorella 



335 



The accumulation of the phosphate compounds under consideration 

 in the absence of CO2 is maximal at pPI ^^ 4, and decreases toward 

 zero at pH 7 to 8. It does not require oxygen and is not affected by the 

 presence of nitrate. It is less sensitive to phenylurethane than photo- 

 synthesis; only the photochemical reaction appears to be affected. 



Photosynthesis and polyphosphate formation are affected by dini- 

 trophenol in mutually similar ways. Also here the effect is greatest at 

 low light intensities. pH has an effect upon this inhibition which can 

 be understood quantitatively if one assumes that the cell membrane 

 is impermeable to the ionic form of the poison, and, moreover, that 



p qP/ m \ 



10 



20 



30 



40 50 60 



10 ergs/ c m^ sec. 



Fig. 2. Fi.xation of orthojihosphate by Chlorella at different light intensities in 

 the presence and in the absence of COs-pH ± 4.0; 25° C; ± 5 mm.''' cells/ml.; 

 iUumination for about 3 hours (3b). 



the internal pH of the cells is se\Tral units above 4 (3b). Sodium 

 azide and sodium fluoride inhibit photosynthesis and polyphosphate 

 formation in much the same way (3b). 



Chromatium was found to excrete inorganic phosphate into the 

 suspension medium in darkness (la). Chlorella mostly hxes some phos- 

 phate, also in darkness. This, however, requires oxygen, contrary to 

 the fixation in light. Under anaerobic conditions a release of phosphate 

 may occur in darkness (31)) ; then the situation becomes very similar 

 to that in Chromatium (la). Dark fixation was found to be less sensi- 

 tive to glucose, phenylurethane, and XaF, but more sensitive to 

 DNP than fixation in the hght. 



