BENT LEY CLASS 



Hs;-; 



aiul ()\cr six times as last at pH 6.5. The reduction ot the (vio 

 chromes was demonstratetl in a cell-lree system by spectrophoto- 

 metric means. The photoprodiiction ol hychogen gas Irom thio- 

 sidfate incHcates that the photosynthetic bacteria are indeed able 

 to reckice TPN and DPN in the light, and with an electron donor, 

 such as succinate, that is at a lower reducing potential than the 

 pyridine nucleotides themselves. 



The Chrotnatium hydrogenase is also capable ot reducing one- 

 electron \ iologen dyes, possessing a low redox potential, and ol evolv- 

 ing hydrogen in the dark Irom the reduced viologen. Succinate, 

 too, is capable ol reducing the cytochromes in cell free preparations 

 of Chromatiuiu. The use in the production of hydrogen gas of the 

 electrons derived from succinate or thiostdfate and raised to the 

 reducing potential of the hydrogen electrode by the action of light 

 of course interrupts the course of electron flow in cyclic photophos- 

 phorylation. Instead, there is a one-way flow of electrons from sub- 

 strate to hydrogen gas. If this flow is also coupled to the phos- 

 phorylation mechanism, a type of non-cyclic photophosphorylation 

 may be envisaged (Fig. 10) . 



From this scheme it is possible to turn to the problem of the 

 production of the primary reductant in photosynthesis in green 

 plants. Arnon and his group have recently found a very direct 

 coupling of photophosphorylation and the photoreduction of TPN, 

 as follows: 



2 TPN -i- 2 ADP -f 2 P -f 2 H.O -^ 2 TPNHo + Oo -f 2 ATP 



(e^.- 



Hydrogenose ,^^f ^. \ 



T — ^yy 



T 



H 



t 

 HA 



\ 



■0 



Chi ' + ;-^ 



•Cyf 



LIGHT -P- 



ADP 



Non- cyclic photophosphorylotion (bacteria) 

 Fig. 10. Scheme for non-cyclic photophosphorylation in Cluomatiuni. 



