206 



Daniel I. Arnon 



the electron donor system. 



Mitsui and Arnon (60) have compared the photochemical activity 

 of two kinds of particles, "blue" and "green", from Nostoc . The 

 blue particles (prepared with carbowax (6I) and dextrin) con- 

 tained both chlorophyll a and phycocyanin whereas the green 

 particles (prepared with carbowax only) contained little of the 

 phycocyanin pigment. 



Table 5 

 Noncyclic Electron Flow in Blue and Green 

 Nostoc Chroma tophores (60) 



Green chroma tophores 

 O2 evolved TPN reduced 

 (jmoles 



O.k 0.9 



0.2 6.2 



As shown in Tables 5 ar^d 6, both blue and green Nostoc parti- 

 cles were able to carry out cyclic photophosphorylation with 

 phenazine methosulfate and photoreduce TPN with the ascorbate- 

 DPIP couple as the electron donor system. However, the green 

 particles had only a feeble capacity for TPN reduction (and 

 oxygen evolution) when water was the electron donor. By contrast^ 

 the blue particles were able to use water effectively as the 

 electron donor for a reduction of TPN and a coupled oxygen evolu- 

 tion. 



Table 6 



Cyclic Photophosphorylation in Blue and Green 

 Nostoc Chromatophores (60) 



Blue chroma tophores Green chromatophores 

 nmoles ATP formed 

 Light 3.8 3.8 



Dark O.5 O.k 



These results are consistent with the view that in particles 

 of blue-green algae, as in chloroplasts, the accessory photo- 

 synthetic pigment is required for photoproduction of oxygen, but 

 not for photophosphorylation and TPN reduction per se . 



Concluding remarks . Extensive work from several laboratories, 

 mainly with intact cells, has led to a now widely held view that 

 photosynthesis in green plants involves the cooperation of at 



