180 



PROBLEMS OF PHOTOSYNTHESIS 



TABLE 23 

 O2 consumption and H2O2 formation in grana (about 1 ^mole chlorophyll) in air, in 0.01 N HCN. 

 0.5 to 1 yumole benzoquinone or /3-naphthaquincne sulfonic acid added. pH 8.3. Incident energy 



about 36 /imoles quanta/min. 



Warburg (21) compared these findings obtained with grana in the presence 

 of quinone with those obtained with Chlorella without quinone. When 

 Chlorella in C02-containing air is illuminated normal photosynthesis is ob- 

 tained. Addition of HCN up to 0.01 A' elicits complete inhibition and no 

 pressure changes are noted; no H2O2 is produced. However, when the O2 

 pressure is increased from 0.2 to 1 atm, considerable negative pressures and 

 H2O2 production are obtained upon illumination but not in the dark. Addi- 

 tion of CO2 accelerates the H2O2 production which can be completely in- 

 hibited by 0.0001 N phenanthroHne. In these experiments the ratio H2O2/O2 

 is not equal to 1. as is the case in simple autoxidation, but has the value 2 

 (Table 24). This means that the reaction equations found for quinone 

 catalysis in grana in 0.01 A^ HCN are the same for Chlorella without quinone 

 in 0.01 A' HCN. Warburg assumes the presence of an oxidant E, which he 

 considers to be an enzyme, in Chlorella. The following reaction scheme can 

 then be applied to Chlorella: 



2E + 2H2O 

 2EH2 + 20 2 



-^ 2EH2 + O2 

 ^ 2E + 2H2O2 



2H2O + O. 



2H2O2 



These experiments prove that Chlorella contains a natural catalyzer which 

 is reduced upon illumination evolving O2. The catalyzer is steadily re- 

 oxidized in the dark. It behaves in the same way as quinone added to grana 

 or Chlorella (see Tables 23 and 24). 



TABLE 24 



O2 consumption and H2O2 formation in 100 yX Chlorella per hour, in 0.01 A' HCN, in 20 vol % 



CO2-O2. pH 4. Incident energy about 36 ^moles quanta/min. 



