BENTLEY GLASS 891 



done by Babette Stern with a spinach chloroplast system that con- 

 firms this effect. In the presence of a catalytic amount of intlophenol 

 dye, the reduction of ferricyanide by the chloroplast system was great- 

 ly enhanced, and even doubled, by CO.j or bicarbonate; and the 

 amount of oxygen evolved luider these conditions agreed quite well 

 \\ith amount of ferricyanide reduced. 



Further observations on the oxygen exchange reaction were con- 

 triliuted by David W. Krogmann. 1 he oxygen exchange was measured 

 by means of the mass 34 isotype of oxygen. The amount of exchange 

 was not markedly affected by the amount of photophosphorylation 

 in the system, but did depend on the presence of the indophenol dye. 

 It did not result in any increase in the formation of hydrogen per- 

 oxide (Mehler reaction, equation 5a) nor in any stoichiometric rela- 

 tion to the amount of phosphorylation occurring. The tentative in- 

 terpretation given by Krogmann is that the dye is reduced in a Hill 

 reaction, with the evolution of oxygen, but w^ithout photophosphory- 

 lation; while a flow of electrons from the photoreductant may pro- 

 ceed to oxygen, with formation of water and accompanying phos- 

 phorylation. 



In the blue-green alga Anabaena variabilis, photophosphorylation 

 has been localized in a phycocyanin-free preparation containing smooth 

 vesicles apparently derived from the peripheral lamellae seen in in- 

 tact cells, according to the report by Barbara Petrack and Fritz Lip- 

 mann. The phosphorylation process is most actively catalyzed by 

 phenazine methosulfate, but FMN and vitamin K (menadione), and 

 especially a combination of the two, also will act as cofactors. Only 

 ADP will serve as phosphate acceptor. Anaerobic conditions proved 

 to be essential, and Petrack and Lipmann suggest that the phyco- 

 cyanin normally present protects the chlorophyll system from photo- 

 oxidation. Glutathione stimulates photophosphorylation in this sys- 

 tem, up to a certain maximum above which there is inhibition owing 

 to an ATPase-like activity. The dephosphorylation thus discovered, 

 and found to be mediated also by cysteine, seems in all respects (re- 

 quirements and inhibitions) to be a photohydrolysis that is a simple 

 reversal of the phosphorylation process. A similar photohydrolysis of 

 ATP was subsequently demonstrated to occur in spinach chloroplast 

 systems. The general significance of the photohydrolysis of ATP in 

 photosynthetic systems will require further elucidation. 



B. L. Strehler and D. D. Hendley describe the use of the firefly 

 luminescent system to measure continuously the generation of ATP 

 by an isolated chloroplast system. Rapid increases and decreases of 



