449 



Norman I. Bishop and H. Gaffron 



that treatment with the uncoupling agent enhanced the rate 3"'+ 

 fold. Nevertheless, this enhanced rate of light induced hydrogen 

 formation remains equally sensitive to inhibition by DCMU as the 

 non-stimulated reaction. CCCP does not inhibit the quinone-Hill 

 reaction or ferricyanide reduction by spinach chl oroplasts. 



Treatment of manganese deficient, and therefore poorly synthe- 

 sizing, cells with CCCP stimulated the previously small rate of 

 Ho production (Fig. 3). And finally, addition of CCCP to adapted 

 "carbon dioxide" mutants of Scenedesmus produced the increased 

 rate of hydrogen evolution, but no effect at all was observed 

 when adapted "oxygen" mutants were treated. 



THE LACK OF INFLUENCE OF FLUOROACETATE AND lODQACETATE 

 ON THE PHOTOHYDROGEN ACTIVITY OF SCENEDESMUS 



Gest and coworkers have recently shov'/n that hydrogen formation 

 by i^hodospi r i 1 lum rubrum occurs in part via an "anaerobic citric 

 acid cycle" during which an exogenous hydrogen donor is oxidized 

 to carbon dioxide and hydrogen^ ''^' ^ °^ . One of their principle 

 experimental findings to substantiate this hypothesis is that 

 fluoroacetic acid inhibits hydrogen formation and citric acid ac- 

 cumulates. In preliminary experiments with monof luoroacetate and 

 iodoacetate no inhibition of photohydrogen evolution was observed. 

 For example, at concentrations of I oAA which abolished photosyn- 

 thesis (3 X 10"^/1) no inhibition of photohydrogen activity occur- 

 red, but rather a stimulation. Similarly 10"^M f luoroacetate, 

 although not inhibitory to photosynthesis, stimulated but did not 

 inhibit the production of hydrogen. 



MASS SPECTROMETER ANALYSIS 



Through the courtesy of Drs. B. Kok and G. Hoch some prelimin- 

 ary experiments were made on their mass spectrometer. The results 

 confirmed our manometric observation (Figs, 1-^, Tables I and II) 

 and in addition, showed that in normal, adapted Scenedesmus oxy- 

 gen, as well as hydrogen, is produced. These data revealed a 

 greater complexity and variability in the time course of rates 

 and ratios for the appearance of the two gases. Similar observa- 

 tions were made a few years ago by Spruit(3). 



CONCLUSIONS 



The data reported here require an interpretation more complex 

 than any previously offered for the mechanism of the production 

 of hydrogen by adapted Scenedesmus cells. It appears quite evi- 



