412 



LIGHT AND LIFE 



possibly a better quantum yield at very weak ones, and different 

 kinetics at 710 m^u, compared to shorter wavelengths. 



As shown in Fig. 11, the rates of PMS photophosphorylation, which 

 were measured at the lull intensity of Fig. 9, show a pronounced 

 maximum at 710 m/x. This effect is the opposite of the well-known 

 drop of the quantum yield beyond 680 m/A that occurs in complete 

 photosynthesis. Whereas in the previous section evidence was pre- 

 sented that the light step leading to formation of "P 700" was con- 

 nected with oxygen evolution, the similar sensitization of the nega- 

 tive absorption shift at 700 m^u, and cyclic photophosphorylation in- 

 dicates a correlation between these phenomena. 



In this connection an initial report by Petrack (19) with cell-free 

 Anacystis prej^arations is of interest. Preparations largely devoid 



0.7 



0.6 



Spinach chloroplasts 



R3te: nM PO-7o min 



0.5 - 



0.4 



0.3 - 



0.2 - 



0.1 



710 mil 



670 mil 



Light Intensity (%) 



Fig. 10. Rate of photosynlhctic phosphorvlation \s. liffht intcnsitv. Flask con- 

 tents: 1 niitroinole inorganic phosphate; '1 micronioies adenosine diphosphate; 

 4 micronioies MgCl.; spinacli chloroplasts containing 2.')0 Mg chlorophyll: 0.1 

 micronioies phena/ine methosiilpiiate; .'> micromolcs "tris" hiifTer, pH 7.4; in a 

 total \oiiime of 0..'{ ml. Fi\c-miiuite reaction time; temperature, 18°C. 



