184 PROBLEMS OF PHOTOSYNTHESIS 



Hill — must be regarded as more or less suspect. Phosphorylation due to the 

 action of light still remains very problematical. Warburg's work in the field 

 of photosynthesis chemistry deals mainly with the importance of COo. His 

 studies with fluoride and with quinone have already resulted in many im- 

 portant discoveries which were discussed in the last section of this chapter. 

 They are all based upon reliable measurements by means of new manometric 

 methods. Warburg found considerable evidence that respiration belongs 

 to the chemical mechanism of photosynthesis. This follows from the one- 

 quantum theory discovered in 1950. In 1958 he found that respiration and 

 photosynthesis decrease in the same proportion at very low Oo pressures 

 (§ 42). The experiments discussed in § 67 showing that no COo fixation with- 

 out respiration can be detected provided further support. Recently War- 

 burg and Kayser (9) measured the CO induced inhibitions of respiration and 

 photosynthesis in cotyledons of barley of various ages (6 to 21 days) and 

 found a significant relationship. When respiration in older leaves was less 

 inhibited by CO, the same decrease in CO inhibition was noted in photo- 

 synthesis. Six day old leaves showed inhibition values of 56% and 59% 

 for the two processes. In 14 day old leaves values of 24% and 20% were 

 found, whereas in 21 day old leaves there was no CO induced inhibition in 

 respiration and in photosynthesis. Thus, these experiments clearly show that 

 when respiration is inhibited to a certain degree, photosynthesis is equally 

 inhibited to the same extent. We may also recall here the inhibitory action 

 of O2 withdrawal upon photosynthesis attributed to the decomposition of 

 glutamic acid (§ 61). 



In § 36 and § 57 we discussed the production of glycolic acid in photo- 

 synthesis of Chlorella. There is evidence that this compound may be of 

 particular importance. Zelitch (24) draws the attention to the central posi- 

 tion of glycolic acid in the processes of respiration and photosynthesis in 

 tobacco leaves. Warburg and Krippahl (19) show that Chlorella suspensions 

 in appropriate carbonate buffer solutions provoking a low CO2 pressure (0.05 

 atm %) produce upon strong illumination (800 jul quanta/min) with pure Oo 

 in the gas phase about one molecule glycolic acid for two molecules CO., con- 

 sumed. In increasing the CO2 pressure, glycolic acid formation is inhibited. 

 At a COo pressure of 1.70 atm % only traces of the acid are detectable. It 

 was possible to separate CO2 fixation and glycolic acid formation. When the 

 gas phase contains 2 atm % CO2 and Oo, it is shown that in the beginning of 

 the experiment COo disappears without formation of glycolic acid. After a 

 while the COo pressure is decreased to such an extent that glycolic acid can 

 be produced in more or less pure Oo atmosphere. The chemical mechanism 

 is not yet elucidated but there is evidence that COo reduction on the one hand 

 (e.g., to glycolaldehyde) and oxidation of the resulting reduction products 

 (e.g., to glycolic acid) on the other hand are competitive reactions with respect 

 to an oxidizing enzyme. This view is in full agreement with the fact that in 

 photosynthesis COo has to be oxidized (to the state of the photolyte) before it 

 can be reduced (19). 



