164 



PROBLEMS OF PHOTOSYNTHESIS 



a chlorophyll peptide composed of aspartic acid, alanine and glutamic acid 

 the last-mentioned being of particular importance in photosynthesis. 



Chlorella contains glutamic acid in concentrations varying from 0.5 to 

 1.3% of the cells' dry weight, depending on the method of cultivation em- 

 ployed. In chlorophyll-rich cells (5 to 8%) 1 to 2 mole glutamic acid is 

 present per mole chlorophyll. It is possible that in such cells all the glutamic 

 acid is bound to chlorophyll. In chlorophyll-poor cells only a part of the 

 glutamic acid is bound to chlorophyll and the remaining part exists in a free 

 state. 



It is an important fact that Oo inhibits the breakdown of glutamic acid. 

 The addition of NaF increases respiration and the energy derived from the 

 increased respiration resynthesizes the decomposed glutamic acid until an 

 equilibrium state is reached between decomposition due to NaF and resyn- 

 thesis due to respiration. Anaerobically, 0.001 A^ NaF completely decom- 

 poses glutamic acid. In the presence of O2 the decomposition is incomplete 

 because of the above-mentioned resynthesis. 



The action of light decreases as the glutamic acid decomposes, and increases 

 as it is resynthesized. Thus, glutamic acid must be closely connected with 

 the light action. Two different NaF concentrations are added, in the pres- 

 ence of O2, to a Chlorella suspension. The decomposition of glutamic acid 

 and the decrease in the light action are measured when the steady state is 

 reached. Table 19 clearly shows the close relationship mentioned (6, 13). 



TABLE 19 

 Glutamic acid and light action 



The objection could be raised that NaF inhibits the light action not because 

 of the decomposition of glutamic acid, but because of some other, unknown 

 reasons. A comparison of the inhibition of the light action by 0.001 A^ 

 NaF under anaerobic and aerobic conditions shows — as already mentioned 

 — that all the glutamic acid is decomposed under anaerobic conditions and 

 that little glutamic acid is decomposed under aerobic conditions. With the 

 same NaF concentration, the inhibition of the light action is very pronounced 

 under anaerobic conditions and very weak under aerobic conditions. Thus, 

 under all conditions the decomposition of glutamic acid runs parallel to the de- 

 crease in the light acdon; it must be concluded that the former is the cause 

 of the latter. The inhibitory action of long-lasting withdrawal of Oo upon 

 photosynthesis must be attributed to the decomposition of glutamic acid. 



