THE CHEMISTRY OF PHOTOSYNTHESIS 



175 



2 mg quinone added. Sample III is shaken with air in the dark for the 

 same time with 2 mg quinone added. The cells are afterwards washed with 

 water, centrifuged and extracted with methanol. Using Willstatter's method, 

 the chlorophylls are removed by saponification and the remaining carotenoid 

 ether solution filled up with ethanol to 100 ml. P'or 1 cm layer thickness 

 In iji is plotted against the wave-length. It follows from Figure 67 that the 

 activation of the oxygenase by means of quinone reduces the carotenoid con- 

 centration in the dark to about 50% of the initial value, but reduces it in the 

 light to about 25% of the initial value. 



160 



— I 1 1 \ I 



80 100 120 140 160 180 200 



Fig. 68. O.xygenase reaction with lyophilized cells of Chlorella. In the manometer vessel 

 3 ml Vso M phosphate, 0.1% KCl (pH 6.5). In the side-arms 25 mg lyophilized cells. Air 

 in the gas phase. KOH in the center well. At time t = 0, the lyophilized cells are tipped into 

 the vessel. Curve I: dark. Curve II: incident intensity of white light 200 yul quanta/ 

 min. Curve HI: incident intensity of white light 750 ^ul quanta/min (Warburg et al., Zsc/ir. 

 Naturf.). 



Figure 68 illustrates the behavior of lyophilized cells in the dark and upon 

 illumination with two light intensities. A suspension of 25 mg lyophilized 

 cells corresponding to 100 tx\ fresh Chlorella consumes 160 /xl O2 in the dark 

 after 190 min (curve I). On illumination the uptake decreases more mark- 

 edly at high light intensities than at lower light intensities (curves II and 

 III). This experiment shows some similarity to the compensation of respi- 

 ration by photosynthesis. However, it should be kept in mind that lyophilized 

 cells produce neither CO2 due to respiration nor Oo from CO2 (see § 63). 



In the manometric experiments discussed certain precautions have to be 

 observed. Lyophilized cells must be brought into the side-arm of the ma- 

 nometer vessel and only at time t = are they tipped into the salt solution of 

 the main compartment, where Oo uptake immediately sets in. If the lyo- 

 philized cells were suspended in the salt solution before the manometric 

 reading, the greater part of the oxidation process would pass unobserved. 

 Precautions are also necessary for the activation with quinone. The center 



