574 



LIGHT AND LIFE 



The electron flow mechanism for the photoproduction of hydrogen 

 from thiosulfate (2) envisages the following electron transfer: 



CHLOROPHYLL 



LIGHT 



THIOSULFATE — =:: — *■ CYTOCHROMES J-EXCITED CHLOROPHYLL 



SULFATE 



HYDROGENASE 



This formnlation provides for a rednction of CJiroinatium cyto- 

 chromes by thiosnlfate. Evidence for this reaction, in a cell-free sys- 

 tem, is shown in Fig. 5. 



PHOTOPRODUCTION OF H2 FROM THIOSULFATE 



/J. moles thiosulfate added ^10 



0-0 none 

 ^^10 (heated cells) 



10 20 30 40 50 

 minutes 



Fig. 4. Photoproduction of hydrogen by Chromatium cells as a function of added 

 thiosulfate. A control treatment included the addition of 10 micromoles of thio- 

 sulfate to cells that had been heated for 10 minutes at 100° C. Other experimental 

 conditions as described for Fig. 1. 



