170 PROBLEMS OF PHOTOSYNTHESIS 



in Figure 64, results in the curves shown in Figure 65. It follows from curve 

 II that photosynthesis with 0.001 A^ NaF is initially inhibited, but reincreases 

 when Oo production changes the initial anaerobic conditions to aerobic con- 

 ditions. Respiration of the cells sets in and this energy resynthesizes glutamic 

 acid, so that photosynthesis can increase again. By ascertaining the glu- 

 tamic acid content at the beginning and at the end of the anaerobic experi- 

 ment in NaF-free controls, the constant value of 1.7 /xmole/100 ^J.\ cells is 

 found. In the presence of 0.001 A^ NaF the glutamic acid content at the 

 beginning of the experiment is zero. At the end it is 1.47 ^mole/lOO ^1 

 cells. Therefore, because of the autocatalytic Oo production the glutamic 

 acid content increases from to 86% of the normal value (1.7 /xmoleTOO 

 /xl cells). During this time photosynthesis increases from a very low value 

 to 82% of its normal value, as follows from the difTerence of the slopes of 

 curves I and II in Figure 65. This quantitative parallelism between the re- 

 synthesis of glutamic acid and the increase of photosynthesis (see also Table 

 19) proves most convincingly the close connection between photosynthesis 

 and glutamic acid. 



For these experiments illumination with high intensity is necessary so that 

 the Oo saturation pressure is obtained within about 10 min in the NaF-free 

 controls. If the intensity is too low, the saturation pressure would not be 

 obtained for one hour, and six hours would be required for the resynthesis 

 of glutamic acid in 0.001 A^ NaF. 



In this type of experiment it is sufficient to know the ratio of the pressure 

 changes in NaF and in the control. However, if the exact amount of the O2 

 produced is to be ascertained, equadon 12 can be used. Owing to the high 

 light intensity, it is permissible to call 7 = —1, so that 



X,,., = /. -/^°^-V =2.8 A Ml 



With regard to the ratio of the pressure changes, it must be borne in mind 

 that in the experiment depicted in Figure 65 COo is bound when glutamic 

 acid is resynthesized. To this amount of COo we have to add the so-called 

 aerobically dissociating COo which will be discussed in § 65. With 10 vol % 

 CO2 in the gas phase, this amounts to about half of the other COo. As 1.47 

 //mole = 1.47 X 22.4 ijl\ glutamic acid is resynthesized, 



xeo, = 1.47 X 22.4 X 1.5 = 49^1 



Hence, the binding of CO2 in NaF elicits the negative pressure change 



_49 _49 

 //CO, = -r — = yrr = -30.5 mm 



It follows from Figure 65 that the difference A in the pressure changes of 

 both curves is 157 mm. The CO2 binding is thus 20% of A. The remain- 

 ing 80% must be attributed to the decreased O2 production, i.e., indicate the 

 inhibition of photosynthesis. 



