THE ENERGETICS OF PHOTOSYNTHESIS 77 



As very small intensities of blue-green light provoke great photochemical 

 activity, Warburg assumes an enzyme mechanism ; a proenzyme is reversibly 

 changed into an enzyme 



with blue-green 

 proenzyme \ ~ ' enzyme 



without blue-green 



The importance of cultivating Chlorella with fluctuating light has been 

 pointed out in § 15. In § 20 we found that the maintenance of an optimal 

 COo pressure is indispensable. The investigations on the effect of blue-green 

 light show a further factor of importance for low quantum requirements. 

 We have seen that good or poor yields can be obtained as desired by adding 

 or removing blue-green light. This may also explain why great'y diff"ering 

 values for the quantum requirement have been obtained in various institutes. 

 Even when manometry and intensity measurements were correctly carried 

 out, neglect of further important experimental conditions (cultivation, CO2 

 pressure, blue-green light) must have led to discrepancies. However, when 

 all the conditions are met, constant low quantum requirements will be ob- 

 tained at constant illumination in experiments lasting several hours (43). 

 Figure 31 shows the results of an experiment lasting 5 hours where the quantum 

 requirement was always about 3. In an experiment lasting 6 hours (Fig. 

 32) the quantum requirement was about 4. Warburg et al. (43, 63, 64) 

 carried out 23 experiments lasting 6 hours with green + blue-green. They 

 found an average quantum requirement of 4.07. One of these experiments 

 gave the high value of 7.51 (see Addendum, page 186). 



The effect of blue-green light is determined by means of the two-vessel 

 method (57). Each vessel is illuminated with red or green measured light 

 and blue-green light. Thus, a total of four light beams are needed each of 

 which is bolometrically measured. Figure 33 depicts schematically the optical 

 equipment with the two ordinary mirrors Al and a semi-transparent mirror 

 M' . The incident intensity of each of the red (or green) beams and of each 

 of the blue-green beams must be exactly identical for both vessels. To 

 begin with, both red (or green) beams are bolometrically adjusted to the same 

 intensity by means of the diaphragms D, the cuvette C being filled with pure 

 water. Afterwards, this cuvette is filled with a solution of HoPtClg which 

 does not absorb red (or green) so that the intensity of the blue-green beams 

 can be adjusted (63). 



Numerical example: 



Determination of the quantum requirement after 2 and 5 hours at constant illumina- 

 tion, using the two-vessel method. Cell suspension: 0.5 ^1 cells/ml. 



A = 8.595 B = 11.05 C = -12.46 D = -18.00 



Measured light: green. Incident intensity 24.8 ^1 quanta/min of which 3.3% is 

 absorbed. 



Blue-green light: 4700 A. Incident intensity 0.95 ^1 quanta/min of which 20% is 

 absorbed. 



