616 



LIGHT AND LIFE 



Q. 



o 



CL 

 CO 



ro 

 to 



CD 

 O 







10 



30 



Hl22 0^ 



120 I 



118^ 

 o 



-116 



o 

 Q. 



ro 



CO 



a 



40 



20 

 Minutes 

 Fig. 1. Measurement of oxygen exchange with the reaction mixture for 



oxidative photophorylation. 



centration of the mass thirty-four isotope, indicating that oxygen 

 from the gas phase is being consumed by the illuminated chloro- 

 plasts. At the same time, an increase in the concentration of the mass 

 thirty-two isotope in the gas phase is observed, indicating that oxygen 

 is being produced from the aqueous phase. These rates of oxygen pro- 

 duction and consumption are nearly equal. When the light is turned 

 off, this oxygen exchange reaction stops. More information about the 

 indophenol-induced oxygen exchange by illuminated chloroplasts is 

 seen in Table 1. The rate of synthesis of ATP during these experiments 

 is quite low because of the damaging effects on the chloroplasts of pro- 

 longed shaking during equilibration and calibration of the mas<; 

 spectrometer. However, the oxygen exchange reaction is seen to be 

 independent of the net synthesis of any considerable amount of ATP, 

 in that the reaction is unaffected by the omission of ADP. Neverthe- 

 less, the high rate of oxygen exdiange is dependent on the presence 

 of indophenol dye. Also, there is negligible exchange activity of the 

 complete reaction mixtine if boiled chloroplasts are used. 



TABLE 1 

 Oxygen Exchange with 2,3',6-Trichlorophenol Indophenol 



Reaction 

 Mixture 



Atmoles P 

 csterificd 



iuatoms O2 

 consumed 



liaXoms O2 

 produced 



complete 

 minus ADP 

 minus dye 



12 

 1 

 3 



53.1 

 58.9 

 22 



42.6 

 53.6 

 14 



Values are reported as rates/mg chlorophyll/hour. 



