450 



Norman I. Bishop and H. Gaffron 



dent that there is niore than a coincidental relationship betv^een 

 a cell's capacity to evolve oxygen on the one hand and hydrogen 

 on the other. The data obtained from mutants whose photosynthet ic 

 apparatus is knovm to be blocked in the oxygen pathway, from stu- 

 dies with known poisons of the oxygen system, and from manganese 

 deficiency experiments support this conclusion. In addition, the 

 simultaneous appearance of hydrogen and oxygen under adapted con- 

 ditions, as determined manometr i cal 1 y and also v/ith the aid of the 

 mass spectrometer, adds further evidence to the hypothesis that 

 both gases appear via a common mechanism. If inc'eed water is the 

 substrate of both hydrogen and oxygen, then the ratio of the am- 

 ounts of the gases formed should be 2. However, it is difficult, 

 if not impossible, to determine this stoi chi ometry in a system 

 which is oxygen starved. Spruit, in attempts to measure the hy- 

 drogen-oxygen ratio obtained the theoretical ratio. of 2 only when 

 he subjected adapted cells to freezing and thawing^-^^. It was 

 assumed that this procedure left intact and active only that por- 

 tion of the photochemical apparatus responsible for the photoly- 

 sis of water. 



Assuredly the mechanism for the photochemical production of 

 hydrogen by photosynthet i c bacteria has been more thoroughly stu- 

 died than the algal system, and from the work of Gest and cowork- 

 ers good evidence is available as to the possible mechanism. Can 

 it be assumed that the same or a similar mechanism is functional 

 in the algal system? The following facts suggest that the answer 

 to this question must be in the negative: (1) Hydrogen production 

 in the bacterial system is suppressed by nitrogen and inhibited by 

 ammonium salts, while In the algae the procees occurs equally well 

 in nitrogen or helium; (2) Uncouplers of cyclic photophosphoryl a- 

 tion Inhibit the bacterial reaction but stimulate the process in 

 Scenedesmus ; (3) Hydrogen production is inhibited by all condi- 

 tions known to interfere with oxygen evolution while the bacterial 

 system is not inhibited by DCMU^^^^ and a manganese dependency 

 would not be expected; (A) Fl uoroacetate, which has been shown 

 to be a potent Inhibitor of the bacterial system does not hinder 

 hydrogen evolution by Scenedesmus ; (5) and finally, the hydrogen 

 evolution in algae requires the two pigment system, i.e., shows 

 the Emerson enhancement phenomenon, and so far no such response 

 has been detected in the photosynthetic bacteria. 



The theoretical meaning of these experiments on the simultan- 

 eous evolution of hydrogen and oxygen In the light becomes rather 

 obvious when v.'e consider that this reaction becomes stronger the 

 more other chemical consequences of the primary process are sup- 

 pressed. The best conditions are those vjhere no reduction of 



