Kinetics of the Photosynthetic Incorporation 



of Radiocarbon 



S. AROXOFF, The Institute for Atomic Research and Departments of Botany 

 and Chemistry, Iowa State College, Am.es, Iowa 



The kinetics of incorporation of radioactive carbon into various 

 compounds in photosynthesizing Scenedesrmis are available (1). C'*02 

 having been incorporated under conditions as near steady state 

 as possible, one may seek to ascertain whether a qualitative cor- 

 respondence may be shown with the known pathway of carbon dioxide 



polymeric CHO's 



Fig. 1 . Scheme for the photosynthetic assimilation of carbon dioxide in Scene- 

 desmus, as proposed by Calvin and co-workers. The reversibility of all of the re- 

 actions within the cycle is presumed but not indicated. Erythrose phosphate is at 

 present still unidentified. Recent findings also suggest the possibility of the for- 

 mation of xylulose as a precursor of ribose. 



assimilation (Fig. 1). The correspondence is sought in two types of 

 curves: (a) the rate of incorporation of isotope into the various com- 

 pounds (including its distribution within the individual moieties) 

 and (6) the changes in concentrations of the compounds during transi- 

 tion from one steady state to another. Required parameters include a 

 knowledge of the respective rate constants and the steady-state con- 

 centrations. Although the latter has been determined (for a par- 



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