THE CHEMISTRY OF PHOTOSYNTHESIS 



171 



It must be emphasized that the reaction 

 CO2 + 7-ainin(jl)ut\ ric acid 



s^lutamic acid 



does not represent CO2 hxation in photosynthesis. The more 7-aminobutyric 

 acid produced, the greater the inhii^ition of photosynthesis. § 65 shows that 

 the aerobically dissociating COo — a great amount of COo fixed in the pres- 

 ence of O2 and removed in the absence of O2 — must be considered to be of 

 utmost importance. This fraction of CO2 is also quantitadvely connected 

 with glutamic acid. If half of the glutamic acid is decomposed by the addi- 

 tion of NaF, photosynthesis and also aerobically dissociating CO2 are halved. 



§ 65 Dissociating Carbon Dioxide 



When Chlorella is saturated at various COo pressures and NaF is added, not 

 only glutamic acid but also bicarbonates develop CO2, e.g., 



H2CO3 + HPO4-- ^ HCO:r + H2PO4- 

 H2CO3 + protein- :^ HCO3- + H-protein 



Furthermore, it may be possible that CO2 originates from carbamino-acids 

 produced in the cells by the action of CO2 upon amino-acids (e.g. glutamic 

 acid). 



COOHCH2CH2CHNHCOOH^COOHCH2CH2CHNH2COOH + CO2 



COOH 



N-carboxyl-glutamic acid • glutamic acid 



The CO2 derived from such carbamino-acids is dependent on CO2 pressure, 

 whereas the CO2 derived from glutamic acid is not dependent on the CO2 

 pressure. 



Warburg (13) found that more CO2 is bound under aerobic than under 

 anaerobic conditions. When, for instance, 100 ^1 cells containing 1.84 

 /zmole chlorophyll and suspended in 3 ml salt solution at pH 3.8 are satu- 

 rated with CO2 pressures varying from 5 to 50 vol %, the amount of CO2 

 removed by Vso A^ NaF in 20 min at 20 °C is as shown in Table 21 . 



TABLE 21 

 Dissociating CO2, anaerobically and aerobically 



If the CO2 removed from glutamic acid at zero CO2 pressure is subtracted 

 from the anaerobic values, the anaerobically dissociating COo is obtained. If 

 the anaerobic values are subtracted from the aerobic values, we find the 



