170 



L. N. M. DUYSENS 



The scheme of Fig. 5 is an attempt to explain various observations. 

 A small part of the bacteriochlorophyll is oxidized by light and simul- 

 taneously a rechieed com])ound H, wliich may 1)C a reduced pyridine 

 nucleotide, is formed. Oxidized bacteriochlorophyll oxidizes one or 

 more reduced cytochromes. The oxidized cytochromes cause the oxi- 

 dation of the substrate and of a small part of H, the last reaction 

 leading to the formation of adenosine triphosphate (ATP), which 

 assists in the reduction of COo. The reactions leading to the reduction 



^ 



lacterio- hv^ J ^ . oxidized 



chlorophyll > ^ bacterio-^ 



j^ ' chlorophyll 



[HJ- 



■'- ADP+P 





oxidized 

 'cytochrome 



substrate 



y^ 



-—[CH20I 



-^ATP 



reduced 

 -cytochrome - 



^>-~., 



oxidized 

 substrate 



Fig. 5. H3'pothetical scheme indicating role of "active" bacteriochlorophyll and 

 of cytochromes in photosynthesis of Rhodospirillum rubrum. 



of COo may be analogous to those in algae. The postulated formation 

 of ATP is in accordance with Frenkel's (7) finding that illuminated 

 extracts of strain 1 produce ATP from ADP and inorganic phos- 

 phate. It should be stressed that the scheme is provisional and in- 

 complete. 



Acknowledgment. Most experiments reported in this paper were carried out 

 in the Department of Plant Biology, Carnegie Institution of Washington, 

 Stanford, California. I wish to thank Dr. C. S. French for continued interest, 

 advice and valuable assistance, Dr. J. H. C. Smith and other members of 

 the Carnegie Institution for friendly advice, and Mr. J. J. Stekert for 

 technical assistance. 



Discussion 



Whittingham : Hill has suggested there is a second cytochrome in Chlorella and 

 Porphyridium which, in the reduced form, has the sharp absorption at 563. You 

 would assume that, if this were reduced in algae and cj^tochrome were oxidized, 

 you would see some change at 563. 



