PHOTOPHOSPHORYLATION AND PHOTOHYDROLYSIS 

 IN CELL FREE PREPARATIONS OF BLUE GREEN 



ALGA 



Barbara Petrack and Fritz Lipmann 



The Rockefeller Institute, Neiv York City 



Our attention was originally attracted to the blue-green algae by 

 a paper from Calvin's group (10) in which a rapid COo fixation into 

 the carbamyl group of citrulline was described. Our earlier interest 

 in carbamyl phosphate synthesis and transcarbamylation reactions 

 prompted us to examine this light-induced carbamylation in cell- 

 free preparations of Nostoc muscorum and Anabaena variabilis. Al- 

 though citrulline was formed rather rapidly by transcarbamylation 

 from carbamyl phosphate to ornithine, the synthesis of carbamyl 

 phosphate from COo, NH3, and ATP, which is the more interesting 

 reaction, was, at best, rather sluggish in these extracts. Furthermore, 

 we soon became convinced that the effect of light on the incorporation 

 of COo into citrulline was indirect and by way of photophosphoryla- 

 tion. We decided, therefore, to turn our attention to the more promis- 

 ing study of photophosphorylation in this system. Although these 

 algae contain the green plant chlorophyll, they have many of the 

 characteristics of a bacterial system; and photophosphorylation was, 

 indeed, found to be similar to that in Rhodospirillum rubrum. Dur- 

 ing a study of this process a photohydrolysis of ATP was observed 

 which strongly impresses us as being a reversal of photophosphoryla- 

 tion. A brief description will be given here of the general characteris- 

 tics of photophosphorylation, as well as the rather novel phenomenon 

 of photohydrolysis. 



Preparation of Cell-free Extracts 



In the following studies Anabaena variabilis was used exclusively. 

 The algae were grown in continuous culture with COo as the only 

 carbon source, essentially as described by Kratz and Myers (9) . We 

 are indebted to Dr. J. Myers for the cultures used as well as for con- 

 siderable information on how to grow them, and to Dr. J. D. Gregory 

 for designing the continuous culture apparatus in which they were 



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