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ENZYMIG MECHANISMS 



OF CARBON DIOXIDE 



ASSIMILATION 



SEVERO OCHOA, assistant professor of biochemistry, new york 



UNIVERSITY COLLEGE OF MEDICINE 



7T IS well known that animal cells depend on a supply of 

 ready-made organic materials (such as carbohydrates, 

 fats, and proteins) or of their building stones (such as simple sugars, 

 fatty acids, and amino acids) for either building up cell substance or 

 replenishing their stores of energy-yielding foodstuffs. Green plants, 

 however, are able to fix atmospheric carbon dioxide under the in- 

 fluence of light and use it to synthesize the organic constituents 

 they need; by means of this process — photosynthesis — they "assimilate" 

 carbon dioxide. In its final over-all results, photosynthesis is essentially 

 a reversal of respiration: In respiration, foodstuffs are oxidized to 

 carbon dioxide and water with absorption of oxygen, the energy thereby 

 released being utilized by the cell to carry out its activities; in photo- 

 synthesis, the chlorophyll-containing chloroplasts utilize radiant energy 

 to build up organic substance from carbon dioxide and water, and 

 oxygen is liberated in the process. 



Some microorganisms, such as green algae and both green and 

 purple bacteria, are photosynthetic. Certain bacteria do not possess 

 the capacity to utilize radiant energy for carbon dioxide assimilation 

 but are able to use, for the same purpose, the energy derived from 

 oxidation of inorganic substances like hydrogen sulfide, thiosulfate, 



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