PHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 377 



nitrogen into cellular substance or for the photoproduction of hydrogen 

 gas. 



s,o.r + 2OH - 



light 



light 



S + SOr + 2e- + H2O 



S + 80H - -^^ SO = + 6f - + 4H2O 



loHoO 



V 10H++10OH- 



Sum : So03= + 5H0O ^^ zSO^ + 8e - + loH + 



The photoproduction of hydrogen gas approached the stoicheiometry 

 of the first reaction, i.e. for one molecule of thiosulphate used, two elec- 

 trons and two protons were combined with the aid of hydrogenase and 

 evolved as Hg. 



' PHOTOPRODUCTION OF Hj FROM THIOSULFATE 



— I r T 1 I 



^moles thiosulfate added -~ 10 



-o-o- none 

 ~~ 10 (heated 



cells) 



10 20 30 40 50 



minutes 



Fig. 20. Photoproduction of hydrogen gas by Chromotiimi cells as a function 

 of added thiosulphate. The control treatment contained cells that have been heated 

 at loo^ for lo min. Other experimental conditions are described for Fig. i6 (Losada, 

 Nozaki, and Arnon [136]). 



With succinate as the electron donor, the proposed sequence of reac- 

 tions which results in the photoproduction of hydrogen is represented as 

 follows : 



Succinate + zFe^ +cyt > fumarate + zFe- +cvt + 2H + 



2Fe2+cyt + 2[Chl] 



-> 2Chl + 2Fe'^ ^cvt 



light 



2Chl— ^-^2[Chl]++2e 



2f'- + 2H + '!I^!Z!!:!!^H2 



Sum : succinate 



light 



> fumarate + H., 



