liESSEL KOK AND GEORGE HOCH 



413 



of phycocyatiiii were found capable of cyclic photophosphorylation. 

 This indicates that chlorophyll a can sensitize this process by itself. 



Simulation of the Light Effects with Chemical Reagents 



We ha\e tried to olHain more insight into the character of the 

 ■P 700" shifts by attempting to reproduce the light-induced changes 

 by chemical means. Two cuvettes, each containing a sample of the 

 same chlorophist suspension, were placed in the paths of a specially 

 constructed double beam spectrophotometer. If the two monochro- 

 matic beams and the two samples are exactly alike, a zero difference 

 signal will be recorded at all wavelengths. Addition of various agents 

 to one of the cuvettes indeed yielded spectral shifts similar to the 

 light-induced ones. As an example, the experiment shown in Fig. 

 12 reveals that under proper conditions addition of PMS results 

 in formation of "P 700," whereas this effect can be reversed by a 

 subsequent addition of ferricyanide. The pigment seems to be oxidiza- 

 ble in the dark only by fairly strong anionic oxidants; quinone, for 



0.5 



0.4 



Rate: jiM P0|/5 min 



0.3- 



0.2 



0.1 



T 



40 



T 



50 



I I r 



70 80 10 700 



Wave Length (mu) 



Fig. 11. Photosynthetic phosphorylation as a function of wavelength. Same 

 experimental conditions as in Fig. 9. Lamp output equal to 100% as shown in 

 Fig. 9. 



