The 

 ^^ carboxylation 

 '^^ reactions 



Thus far we have mentioned two carboxylation reactions 

 in photosynthesis: carboxylation of RuDP (the carbon re- 

 duction cycle) and carboxylation of PEPA. When algae 

 have been allowed to photosynthesize for less than a minute, 

 virtually all the radioactivity found on the chromatogram 

 prepared from the algae is located in compounds apparently 

 derived from these two reactions. There still remained the 

 possibility that other carboxylation reactions might occur 

 which would involve intermediate compounds too unstable 

 or too volatile to be seen on the chromatograms. These pos- 

 sibilities were tested by making a quantitative comparison 

 between the rate of uptake of C^^02 from the medium and 

 the rate of appearance of C^* in compounds on the chromato- 

 grams (3). 



For these experiments, the algae were kept, as close as 

 possible, in steady-state growth in the experimental vessel. 

 Light, temperature, pH, and supply of inorganic nutrients 

 were kept constant. Gas was circulated through the algae 

 suspension in a closed system by means of a pump. Levels of 

 CO2, O2, and, when present, C^^Oo, were continuously 

 measured and recorded. From the known gas volumes of the 



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