CARBON-14 PREILLUMINATION EXPERIMENTS 



217 



ing the R level increased with O2 partial pressure (Fig. 4) and was 

 reversible. 



Figure 5 shows that the decay of R was markedly accelerated by the 

 presence of O2. 



Quinone reacts with R in much the same manner as does O2 except 

 that, in high quinone concentration, inhibition is irreversible (Fig. 6). 

 The C02-fixing power of cells is not restored even by repeated wash- 

 ings wuth phosphate buffer after light exposure in the presence of 



20 



40 50 GO 



TIME IN MINUTES 



Fig. 7. Effect of quinone (lO"''-' M) on the decay of R in the dark. The algae 

 were first illuminated for 50 minutes in the absence of quinone, and simultane- 

 ously with turning off the light, quinone was added and the subsequent fate of R 

 was followed by measuring 30-second Ci*02-fixation in the dark. 



2 X 10-* M quinone. With 5 X 10"* M quinone (Fig. 7) the decay 

 of the R level in the dark is greatly accelerated, as is the case for the 

 analogous experiment using O2 instead of quinone. 



When we investigated the effect of cyanide on the processes of for- 

 mation and decay of R, it appeared that this poison did not affect 

 formation of R, except in so far as the second induction was 

 eliminated. This latter observation corresponds to the observa- 

 tions of McAlister and Myers (3) and of Aufdemgarten (4) on the 

 influence of cyanide on the induction phenomenon occurring in the 

 photosynthetic CO2 uptake. However, when R was formed by pre- 

 illumination for 50 minutes in the absence of cyanide and subse- 

 quently measured by exposure of the cells to C'^O? in the presence of 

 varying amounts of cyanide, it was observed, in confirmation of 



