198 



Daniel I. Arnon 



lations would be expected to be affected. 



Table 2 

 Inhibition of Cyclic Photophosphorylation with Cysteine (22) 



^lmoles ATP 

 Additions formed 



Methyl viologen 5*2 



Methyl viologen, cysteine 0.3 



Vit. K3 6.6 



Vit. K3, cysteine 0.2 



FMN ^.8 



FMN, cysteine 0.4 



PMS 3-6 



PMS, cysteine 3*6 



Photoproduction of hydrogen gas by chlorop lasts . The ability 

 of spinach chloroplasts to photoreduce methyl viologen--a dye 

 used as an electron carrier for hydrogenase (24) --suggested that 

 spinach chloroplasts would also be capable of photoproducing 

 hydrogen gas, if they were supplied with a hydrogenase (which 

 they lack) and if oxygen production, usually deleterious to hy- 

 drogenase activity, were suppressed. 



Photoproduction of hydrogen gas by spinach chloroplasts supple- 

 mented with bacterial hydrogenases was demonstrated by Mitsui and 

 Paneque (25-2?) . When photoproduction of oxygen gas was suppres- 

 sed and cysteine-DPIP (Fig. 2) was used instead of water as the 

 electron donor system, spinach chloroplasts evolved hydrogen gas 

 in the light. The photoproduction of hydrogen gas was accompan- 

 ied by formation of ATP (Fig. 3). 



Ferredoxin and the equivalence of light and Hg for TPN reduc - 

 tion . At first, photoproduction of H2 by chloroplasts was car- 

 ried out with the aid of a hydrogenase isolated from Chroma tium 

 (25,26) or Desulfovibrio desulfuricans (26). In both these cases 

 photoproduction of H2 required the addition of methyl or benzyl 

 viologen (24). However, with a crude hydrogenase from Clostrid - 

 ium pasteurianum no addition of viologen dye was required for the 

 photoproduction of hydrogen gas by chloroplasts (27). The cell- 

 free extract of C. pasteurianum contained an electron carrier 

 which brought about a photoproduction of hydrogen gas by chloro- 

 plasts. This was consistent with the isolation by Mortenson et 

 al. (28) of a natural electron- transferring factor in C. pasteur - 

 ianum . named by them ferredoxin, which, in that organism, couples 



