Robert B.Withrow 403 



compounds such as adenosine triphosphate. Kalckar (26) and Lipmann 

 (52) have very thoroughly reviewed the biochemistry of this subject. 

 The role of phosphorus in the upgrade flow of energy in such organisms 

 as the chemautotrophic bacteria which reduce carbon dioxide by the 

 oxidation of reduced compounds as sulfur and hydrogen and in the 

 photosynthetic organisms has been investigated only recently. 



Vogler and his co-workers (5^) have studied the exchange of phos- 

 phorus between cells of Thiobacilhis thiooxidans and their environ- 

 ment in relation to the oxidation of sulfur and the utilization of car- 

 bon dioxide. This organism is a sulfur bacterium which synthesizes 

 the materials needed for cell growth by the fixation and reduction of 

 carbon dioxide with energy derived from sulfur oxidation. In the 

 absence of carbon dioxide, Vogler found that sulfur can be oxidized 

 and the energy stored within the cell and used later for the fixation of 

 carbon dioxide under conditions unfavorable for sulfur oxidation. It 

 was not determined experimentally whether the energy stored in this 

 case could also be used for the reduction of carbon dioxide. It was sug- 

 gested that, during sulfur oxidation in the absence of carbon dioxide, 

 some of the energy is stored as phosphate bond energy and later used 

 for carbon dioxide fixation with the release of inorganic phosphate. 



During sulfur oxidation it was observed that, in the absence of 

 carbon dioxide, inorganic phosphate was taken up from the external 

 medium. Subsequently, in the absence of sulfur oxidation and in the 

 presence of carbon dioxide, some phosphate was released to the external 

 medium, presumably by the breakdown of energy-rich phosphate com- 

 pounds synthesized during the sulfur oxidation phase. However, dur- 

 ing normal sulfur oxidation in the presence of an adequate supply of 

 carbon dioxide, no appreciable exchange of phosphate occurred, as 

 phosphorylation and dephosphorylation presumably were in equi- 

 librium. Adenosine triphosphate was identified as one of the phosphate 

 compounds formed during the oxidation of sulfur and is possibly the 

 phosphorylated storage product. Vogler suggested that in photosynthe- 

 sis, energy from light absorption may be stored in a similar manner in 

 high-energy phosphate bonds of phosphorylated compounds and later 

 released for the fixation of carbon dioxide. 



Ruben (44) measured the free energy of carbon dioxide fixation in 



