170 PRIMARY PHOTOCHEMICAL PROCESS CHAP. 7 



of oxidizing the less stable ''substitute reductants" (H2, H2S, S2O3 , 

 etc.). (Again, the simplest explanation of the difference between Z^ and 

 Z^ is their identification with chlorophyll and bacteriochlorophyll respec- 

 tively.) 



It may further be asked whether the primary oxidation product Z^ 

 is the same in all purple bacteria, or whether it may further depend on 

 the specific nature of the reductant (H2S, or S2O3 , or H2, etc.). Was- 

 sink, Katz, and Dorrestein (1939) noticed that, in the spectra of living 

 purple bacteria, the single absorption band of free bacteriochlorophyll in 

 the far red is replaced by several red and infrared bands whose pattern 

 varies from species to species (Vol. II, Chapter 22), and suggested that 

 each of these bands corresponds to a different bacteriochlorophyll-bearing 

 complex adapted to the reduction of a specific hydrogen donor. How- 

 ever, this hypothesis disagrees with the assumption, made in chapter 6, 

 that the hydrogenase system, even if it acquires hydrogen from different 

 donors by means of specific "oxidoreductases," transfers it to a common 

 acceptor (designated by Ah in Chapter 6). This seems to leave no place 

 for a specific photocatalyst between Ah and carbon dioxide. 



Bibliography to Chapter 7 

 The Primary Photochemical Process 



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1916 Hoffmann, K. A., and Schumpelt, K., Ber. deut. chem. Ges., 49, 303. 



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1936 Stoll, A., Naturwissenschaften, 24, 53. 



