METABOLIC ASPECTS 



137 



200 



B, "GLUTAMATE CELLS" 



100 200 



MINUTES 



20 40 60 80 100 



MINUTES 



'resting' cells of R. rtibrum de- 

 I- glutamate (B.) medium. After 



Fig. 1. Kinetics of photoproduction of H2 by 

 rived from a malate + NH4''" (A.) or malate 

 Ormerod and Gest (13). 



In A., the cells were harvested while ammonia was still present in the cul- 

 ture medium. Except for the endogenous control in B., L-malate was added at 

 zero time. For other experimental details, see ref. 13. 



apparatus from the complex cellular matrix may result in significant 

 alteration or even total loss of certain biochemical characteristics. 



Remarks on the absence of oxygen production in bacterial photosyn- 

 thesis 



Before the discovery of light-inducedphosphorylation, the similari- 

 ties and differences in the autotrophic metabolism of green plants and 

 photosynthetic bacteria could be visualized mainly in terms of forma- 

 tion and subsequent fate of a photoreductant and a photooxidant. Ac- 

 cording to the concept developed by van Niel (2), the photoreductant 

 would be used for reducing CO2 in both types of organisms, while dis- 

 posal of the photooxidant presumably occurs through alternative 

 routes, i.e., conversion to O2 in green plants and reduction of the po- 

 tential 02-precursor by the accessory electron donor in the bacteria. 



An appealing experimental system for investigating this hypothesis 

 is furnished by green algae which can switch by '^anaerobic adapta- 

 tion" from typical green plant photosynthesis to a bacterial- type of 

 photoreduction of CO2 with H2 (42). The change is reversible in that 

 O2 formation is resumed if the anaerobic algae are exposed to high 

 light intensities. In a recent extension of studies with such organisms. 

 Bishop (43) has isolated a mutant of Scenedesmus obliquus which 



