ON THE INTERRELATION OF THE MECHANISMS FOR OXYGEN AND HYDROGEN 



EVOLUTION IN ADAPTED ALGAE 



Norman 1. Bishop and H. Gaffron 



In 19^2 Gaffron and Rubin discovered that anaerobically adapt- 

 ed cultures of the green alga, Scenedesmus obliquus , strain D^, 

 in the absence of carbon dioxide, produced molecular hydrogen in 

 the lightvO. A few years later a similar process was found to 

 be a part of the metabolism of certain photosynthetic bacteria^ '. 

 In the intervening years only sporadic studies have been conduct- 

 ed on the process as carried out by green algne, but the process 

 of hydrogen evolution in bacteria has been intensively studied by 

 Kamen, Gest and a number of their students. As a consequence, it 

 has been generally assumed that the mechanism of hydrogen produc- 

 tion in the two different systems was probably identical. Hov;- 

 ever, Spruit's studies on the anaerobic gas metabolism of illumi- 

 nated Chloral la Indicated that this was an assumption still open 

 to question. He observed what appeared to be a simultaneous 

 production of hydrogen and oxygen and hesitantly suggested that 

 both gases arose via the photolysis of water''-^'. Hov/ever, he fa- 

 vored the alternate hypothesis that the two gases arose via dif- 

 ferent pathways, i.e., oxygen arose from an endogenous Hill reac- 

 tion while hydrogen came from the dehydrogenati on of some unknown 

 hydrogen donor. 



While studying the physiological characteristics of certain 

 photosynthetic mutants recently induced and Isolated In this lab- 

 oratory, studies on the mechanism of hydrogen production in green 

 algae have been resumed. It is the purpose of this communication 

 to demonstrate the strong interdependence between the mechanisms 

 for the production of hydrogen and of oxygen. if all the major 

 synthetic reactions of Scenedesmus are eliminated or inhibited, 

 the chlorophyll system will evolve upon illumination both molecu- 

 lar hydrogen and molecular oxygen. Any condition which is known 

 to block preferentially the mechanism of oxygen evolution equally 

 Inhibits the mechanism for hydrogen formation. 



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