PHOTOSYNTHESIS 



of carbon dioxide, though to only about 3% of the rate of photo- 

 synthesis. Boychenko and Baranov (7) have demonstrated the 

 incorporation of carbon dioxide into reduced organic compounds 

 by isolated chloroplasts under illumination. This incorporation 

 was determined through use of carbon-fourteen labeled CO2, 

 providing a very sensitive method for detecting reduced carbon. 

 This result recently has been confirmed by Arnon et al. (2). The 

 rate of carbon reduction compared with the rate of carbon 

 reduction in a corresponding amount of photosynthesis in intact 

 leaves was not more than 0.5%, and many of the intermediates 

 of the carbon reduction cycle have not yet been found. In any 

 event, if it turns out that the rate is small compared with photo- 

 synthesis and that only some steps involved in the complete cyclic 

 reduction during photosynthesis are present in the isolated 

 chloroplasts, these facts may be taken merely as an indication 

 that some of the factors involved in the rather complex reduction 

 cycle have been lost from the chloroplasts during their isolation, 

 or that only limited amounts of the necessary enzymes are carried 

 down with them. 



We could think of the chloroplast as a container of a complex 

 arrangement of enzymes and cofactors, some of which are lost 

 when the chloroplast is removed from the cytoplasmic environ- 

 ment of the cell. Possibly such loss could be prevented if the 

 chloroplasts could be preserved throughout their isolation in a 

 solution exactly duplicating that contained in the cell. Perhaps 

 it would be worth while to prepare such a solution by disrupting 

 cells and removing chloroplasts and cell-wall fragments by 

 centrifugation. This solution could then be used during the 

 preparation of chloroplasts from fresh cells. 



The difference in susceptibility to inactivation during chloro- 

 plast isolation displayed by the carbon-reducing apparatus as 

 compared to that found with the system for the photolysis of 

 water can be considered as a difference in susceptibility to loss of 

 factors or to the disruption of the organization of various systems. 

 It appears that the enzymatic apparatus for the absorption of light, 

 the conversion of light energy to chemical energy, the decom- 



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