photosynthesize at a rapid rate if illuminated from each side 

 in a thin transparent vessel. The CO2 is continually taken 

 up from the solution (where it is in equilibrium with bicar- 

 bonate ion) and converted by the photosynthetic plant 

 through a series of biochemical intermediates to various 

 organic products. 



A solution of radioactive bicarbonate, HC^'^Oa-, is sud- 

 denly introduced into the algae suspension. The plant does 

 not distinguish in any important way between the C^^ ^nd 

 C^*, which are chemically almost identical. Immediately some 

 of the C^* is incorporated into the first of the biochemical 

 intermediate compounds. As time passes the C^* gets into 

 subsequent intermediates in the chain. After a few seconds 

 exposure to the C^^02, the suspension of algae is run into 

 methanol to a final concentration of 80 per cent methanol. 

 This treatment denatures all the enzyme instantly and freezes 

 the pattern of C" labeling by preventing further change. 

 Now the dead plant material is analyzed for radioactive com- 

 pounds to see which are the first stable products of carbon 

 reduction during photosynthesis. 



The first step in this analysis is to prepare an extract 

 of the soluble compounds. The early products of carbon 

 reduction have been found to be simple soluble molecules. 

 This extract is then concentrated and analyzed by the method 

 of two-dimensional paper chromatography (12). The impor- 

 tance of the method for these studies stems from the fact that 

 it permits the analysis of a few micrograms or less of dozens 

 of different substances in a single simple operation. 



Of these many compounds, those into which the plant 

 incorporates C^^ during its few seconds of photosynthesis 

 with HC^'^Os- are radioactive and omit the particles result- 

 ing from radioactive decay of the C^". In this case these are 

 13 particles, and these may be detected by the fact that they 

 expose x-ray film. Thus, if a sheet of x-ray film is placed in 

 contact with the two-dimensional paper chromatogram, sub- 

 sequent development of the film will show a black spot on 

 the film corresponding to the exact shape and location of 



13 



