that proceeds in the dark, and PGA continues to be formed 

 in the dark. Could the carboxylation of ribulose diphosphate 

 to form PGA be the first step in carbon dioxide reduction? 

 To answer this question, an experiment similar to the one 

 just described was performed. This time, however, instead 

 of turning off the light, the light was left on, and carbon 

 dioxide was suddenly removed (19). The result of this ex- 

 periment was that the concentration of ribulose diphosphate 

 now rose rapidly while PGA dropped rapidly. Thus the car- 

 boxylation of RuDP to give PGA was confirmed. 



20 



