THE CHEMISTRY OF PHOTOSYNTHESIS 



169 



The aerobic resynthesis of glutamic acid should not be considered to be a 

 simple reversal of the anaerobic decarboxylation reaction. As the resynthe- 

 sis occurs only under aerobic conditions. O2, i.e., respiration, must be indis- 

 pensable. In fact, when small amounts of NaF are added to Chlorella under 

 aerobic conditions, respiration increases. 



§ 64 The Necessity for Glutamic Acid in Photosynthesis 



The foregoing paragraphs have shown that, upon addition of NaF, the 

 glutamic acid of Chlorella can be decomposed and resynthesized by alternat- 

 ing anerobic conditions and aerobic conditions. It has been found that 

 0.001 tV NaF inhibits photosynthesis anaerobically but not aerobically. The 

 decomposition of glutamic acid and the inhibition of photosynthesis on the 



>A=157mr 



20 30 40 50 60 

 Duration of illumination in mm 



fig. 65. Influence of NaF on photosynthesis under anaerobic conditions changing into 

 aerobic conditions. This experiment is the continuation of the experiment in Fig. 64, at the 

 end of which the composition of the gas phase was changed to 10 vol % COo and 90 vol % 

 argon. After 50 min anaerobiosis in the dark glutamic acid is decarboxylated. At / = 

 illumination with 200 jx\ quanta^min. pH, temperature and vessel constants as in Fig. 64. 

 Result: initial marked inhibition of photosynthesis steadily decreasing with increasing O2 

 pressure and resynthesis of glutamic acid (curve II) (Warburg et al., Zschr. Xaturf.). 



one hand, and the resynthesis of glutamic acid and the reincrease of photo- 

 synthesis, on the other, are simultaneous processes. Figure 64 shows an 

 aerobic experiment without NaF and with 0.001 A^ NaF described by War- 

 burg (17). The gas phase contains, initially, 10 vol % CO2, 30 vol % O2 

 and 60 vol % argon. Under these aerobic conditions, photosynthesis is 

 not inhibited by 0.001 A^ NaF. After changing the content of the gas phase 

 to 10 vol % CO2 and 90 vol % argon, anaerobic conditions set in. The ves- 

 sels are shaken for one hour in the dark so that all the glutamic acid is decom- 

 posed. Illumination with the same intensity as in the experiment depicted 



