176 PROBLEMS OF PHOTOSYNTHESIS 



well of the manometer vessel should contain KOH, as is shown, for instance, 

 in Figure 19. The addition of quinone produces CO2 from glutamic acid 

 and this CO2 must, of course, be absorbed by KOH. However, the quinone 

 added may distil into the KOH where it may be oxidized to tetrahydroxy- 

 quinone. This reaction also consumes Oo. For this reason, it is necessary 

 to carry out control studies without cells and to subtract the pressure changes 

 obtained in the controls from those obtained in the experiment. There is a 

 further complication: on illumination quinone produces Oo (Hill reaction). 

 To avoid this, quinone should be completely reduced : this can be done by 

 means of brief illumination with very high light intensity. Otherwise, the 

 O2 production due to quinone would prevent the correct measurement of Oo 

 uptake due to the carotenoid oxygenase. Thus, there are so many sources of 

 error in the activation with quinone that it is preferable to use lyophilized 

 cells to measure oxygenase activity. 



§ ^1 Experiments with Quinone 



When quinone is added to Chlorella in the dark and under anaerobic con- 

 ditions, a considerable amount of CO2 is developed in a short time, and qui- 

 none is reduced to hydroquinone. The amount of quinone reduced is not 

 equivalent to the amount of CO2 produced. The major part of the CO2 pro- 

 duced originates from decarboxylation of glutamic acid, a reaction which is 

 not an oxidation process. Warburg and Krippahl (18) found that addition 

 of 0.1 mg quinone gives the greatest CO2 production, whereas addition of 

 2.0 mg quinone elicits the smallest production of CO2. Whereas 0.1 mg 

 quinone added to 100 jul cells in 3 ml salt solution K has no poisoning effect, 

 0.2 mg quinone inhibits O2 respiration and, therefore, photosynthesis com- 

 pletely and irreversibly. It has been found that, for instance, after addition 

 of 0.1 mg quinone the end value of 57 /xl CO2 developed from 100 /xl cells was 

 attained after 30 min. Of this amount, 40 /xl CO2 were due to glutamic acid 

 breakdown; the origin of the remaining 17 /xl CO2 was unknown. 



Similar experiments in the dark under aerobic conditions also show that 

 0.1 mg quinone does not inhibit O2 respiration but that 0.2 mg quinone does. 

 However, under these conditions O2 is used to a great extent without CO2 pro- 

 duction, due to the action of the carotenoid oxygenase. 



The light reaction of Chlorella with quinone has been discovered by ma- 

 nometry with KOH in the center well of the vessels (3), so that the influence of 

 CO2 could only have been observed with very low CO2 pressures. In these 

 experiments the pH should be low and constant (3.8) to decrease the bicar- 

 bonate content of the medium as much as possible. The suspension of 100 

 lA cells in 3 ml salt solution K is previously treated with 0.1 mg quinone in the 

 dark to drive out the major part of the labile COo. The suspension is first 

 aerated with argon and a little CO2 for 20 min. After closing the stop cocks, 

 the vessels are shaken — also in the dark — for 40 min. Afterwards, 2 mg 

 quinone are tipped from the side-arm and strong illumination (725 /jlI quanta/ 



