444 



Norman I. Bishop and H. Gaffron 



Additional mutant strains of Scenedesmus have been isolated in 

 which the genetic block resides in the carbon dioxide reducing 

 side of photosynthesis (to be referred to as "carbon dioxide mu- 

 tants"). All of these evolve oxygen in the quinone-Hill reaction 

 and produce hydrogen in the light under the appropriate circum- 

 stances (Table II). 



Table II. Gas Metabolism of Adapted Carbon Dioxide Mutants 



of Scenedesmus Do 



1000 ul cells in 3 cc of 0.05M phosphate buffer, pH = 6.5. Tem- 

 perature = 25°C. Gas Phase = N2. 0.2 cc 10% KOH in center well 

 of each vessel. CCP (final concentration = lO'^M) added after 

 adaptation. Period of adaptation = l4 hours. Light Intensity = 

 900 lux. 



From such observations the following question becomes apparent; 

 How close a correlation exists between the capacity for oxygen 

 evolution and that for hydrogen evolution in a normal cell? To 

 explore this possible relationship further, other situations were 

 examined wherein the mechanism of oxygen evolution is believed to 

 be specifically blocked to determine if a parallel inhibition of 

 photohydrogen production also occurs. 



