5. Phosphate Metabolism 



Light-Induced Phosphorylation by Cell- Free 

 Preparations of Rhodo spirillum rubrum* 



ALBERT W. FRENKEL,t Department of Botany, Vniversitij of Minnesota, 



Minneapolis, Minnesota 



Cell-free preparations of the nonsiilfur purple bacterium Rhodo- 

 spirillum rubrum when illuminated with white or red light under 

 anaerobic conditions (to avoid complications due to photooxidation 

 (1)) will esterify orthophosphate in the presence of ADP (Fi^. 1) (2) 

 which is transformed into ATP in an almost ciuantitative manner in 

 the presence of a moderate excess of orthophosphate (3). Certain 

 other substances can act as acceptors for the high-energy phosphate 

 formed in the light as listed in Table I, 2. The rate of phosphoryla- 

 tion is influenced by light intensity as indicated in Fig. 2. All 

 observations reported in Table I refer to experiments performed 

 under anaerobic conditions and at saturating light intensities. 



Crude cell-free preparations as indicated in Table I can use the 5' 

 isomers of AMP, ADP, and IDP as acceptors of the high-energy 

 phosphate formed as a result of the photochemical reaction. The 

 initial rates of phosphate esterification in the presence of any one of 

 these three acceptors do not differ by more than ±5%. Additions 

 of a number of substances (Table I, 4) have little or no effect on the 

 initial rates of phosphorylation or on the total amount of orthophos- 

 phate esterified for a given amount of added phosphate acceptor. 



When a crude cell-free preparation is subjected to further differ- 



* Abbreviations used: AMP, ADP, ATP for the 5' isomers of adenosine mono- 

 phosphate, diphosphate, and triphosphate, respectively; IMP, IDP, ITP for the 

 5' isomers of inosinic acid, inosine diphosphate, and triphosphate, respectively; 

 DPN for (oxidized) diphosphopyridine nucleotide. 



t The author wishes to express his appreciation for the support and helpful 

 advice given to him by Dr. F. Lipmann, and to Drs. A. Brodie and A. H. BrowTi 

 for their many constructive suggestions. This investigation is supported by funds 

 from the Graduate School of the University of Minnesota and by a grant from the 

 National Science Foundation. 



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