THE CHEMISTRY OF PHOTOSYNTHESIS 



177 



min) sets in. It was found that at ClOo pressures between 0.125 vol % and 

 1.49 vol % the end values for the O- produced are practically idendcal. 

 They are equivalent to the amounts of quinone added. However, the rates 

 of O.. production increase with the CO2 pressures. Under 0.015 vol % CO2 

 the rates are very low (Fig. 69). These experiments can only be explained if 

 we admit that CO2 is an intermediate product of the Hill reacdons, as has 

 been proved in other ways for the Hill reagents: NO3 ions and ferric ions 

 (see §49). 



10 15 20 



Duration of illumination in mm 



25 



Fig. 69. Influence of CO2 pressure on the quinone light reaction. In the main com- 

 partment, 100 yul Chlorella (south cells) suspended in 3 ml salt solution K + 0.1 mg qui- 

 none. In the side-arm 2 mg quinone dissolved in 0.2 ml water. In the gas phase argon 

 with various contents of CO2. Illumination; 725 /il quanta/min (Warburg et al. Zschr. 

 Naturf.) . 



In isolated grana and in lyophilized cells of Chlorella the Oo evolution in the 

 light upon addition of quinone proceeds twice as quickly when the gas phase 

 contains 1 .4 vol % COo in addition to argon. In the grana the end value for 

 the Oo produced is the same whether the gas phase contains, besides argon, 

 CO2 or not. It corresponds to about 83% of the amount of quinone added. 

 The end values for O2 production in lyophilized cells are also independent 

 of the presence of CO2 in the gas phase. They are about 50% of the values 

 calculated from the quinone turnover (17). 



The investigations discussed in this paragraph are still being carried out in 

 Warburg's institute. The results already obtained clearly show the prime 

 importance of CO2 in the Hill reactions. 



