Photosynthetic Carbon Dioxide Fixation by Broken 



Chloroplasts* t 



M. B. ALLEN, F. R. WHATLEY, LAWSON L. ROSENBERG, J. B. 

 CAPINDALE, and DANIEL L ARNON, Laboratory of Plant Physiology, 

 Departme7it of Soils and Plant Nutrition, University of California, Berkeley, 



California 



Whole chloroplasts isolated from spinach leaves by grinding in 0.35 

 M sodium chloride or 0.5 M sucrose have previously been found to 

 fix carbon dioxide when illuminated (1,2). The fixation of carbon di- 

 oxide was strictly light-dependent (1,2). The rate of carbon dioxide 

 uptake was proportional to the amount of chloroplasts added, indi- 

 cating that all the components necessary for the process were con- 

 tained in the chloroplast (2). 



Further investigation showed that illuminated whole chloroplasts 

 carried out the complete process of photosynthesis. Fixation of carbon 

 dioxide was found to be accompanied by the evolution of an approxi- 

 mately equivalent quantity of oxygen (2). Examination of the com- 

 pounds formed from carbon dioxide showed that 30% to 40% of 

 the CO2 fixed was converted into starch (2). A study of the soluble 

 compounds by means of paper chromatography and radioautography 

 revealed a pattern similar in some respects to that found after assim- 

 ilation of carbon by whole cells. The principal products identified 

 in the chromatograms were mono- and diphosphates of hexoses and 

 pentoses and dihydroxyacetone phosphate. Glycolic and malic acids, 

 alanine, glycine, and free dihydroxyacetone were also found (2), as 

 was free glucose. 



Until very recently, photosynthesis by isolated chloroplasts was con- 

 sidered to be strictly dependent on the structure of the intact chloro- 

 plast. Disruption of this structure by treatment with water resulted 

 in the complete loss of abihty to fix CO2 (3,4). However, it was found 



* Abbreviations: Pi, whole chloroplasts; Piw, water-treated chloroplasts; CE, 

 chloroplast extract; ATP, adenosine triphosphate; DPN, TPN, di- and triphos- 

 phopyridine nucleotides; FDP, fructose-l,6-diphosphate. 



t Aided by grants from the National Institutes of Health and the Office of 

 Naval Research. 



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