148 ANAEROBICALLY ADAPTED ALGAE CHAP. 6 



period of four minutes appears in light, during which no hydrogen is 

 consumed at all. Obviously, the supply of hydrogen from glucose or 

 its metabolic derivatives suffices to cover all requirements in the dark, 

 and to eliminate the absorption of hydrogen from outside in the first 

 four minutes of illumination. After that, the more rapidly diffusing 

 molecular hydrogen enters into competition with the slower diffusing 

 glucose. A complete inhibition of hydrogen uptake has been observed 

 when yeast autolysate is used instead of glucose. 



The explanation of the photoreduction by adapted algae is contained 

 in scheme 6.1. It is due to the "interception" of the photochemical 

 oxidation products by the hydrogenase system, with the cellular hydrogen 

 donors R'H2 and external hydrogen competing as suppliers of hydrogen 

 to the intermediate reductant, H2AH (c/. Schemes 6. II and 6. III). The 

 evolution of oxygen is probably prevented not only by this interception 

 (which, as noted on page 135, is not perfect), but also by the de-activation 

 of the "deoxidase," Eo (page 134). 



The photosynthesis of green and purple bacteria may proceed by 

 exactly the same mechanism as the photoreduction by adapted algae 

 (except that their enzymatic system is "frozen" and under no circum- 

 stances can switch over to the liberation of oxygen) ; but more probably, 

 the incapacity of purple bacteria to produce oxygen is caused by a 

 different character of the primary oxidation products, Z, which do not 

 contain sufiicient energy for transformation into {O2} and free oxygen, 

 and can only be reduced by the hydrogenase system (c/. Chapter 7, 

 page 169). 



Despite the analogy between the metabolism of adapted algae and 

 purple bacteria, there is a difference in the role which this metabolism 

 can play in the life of these plants: Gaffron (1943) found that, after 

 several days of "photoreduction," the algae showed no multiplication or 

 increase in chlorophyll concentration comparable to that caused by a 

 similar period of photosynthesis. 



Bibliography to Chapter 6 



The Metabolism of Anaerobically Adapted Algae 



1927 G6n6vois, L., Biochem. Z., 186, 461. 



1931 Stephenson, M., and Stickland, L. H., Biochem. J., 25, 205, 215. 



1934 Roelefson, P. A., Proc. Acad. Sci. Amsterdam, 37, 660. 



1935 Gaffron, H., Biochem. Z., 275, 301. 



1937 Nakamura, H., Acta Phytochim. Japan, 9, 189. 



1938 Nakamura, H., ibid., 10, 259. 

 Nakamura, H., ibid., 10, 271. 



Yamagata, S., and Nakamura, H., ibid., 10, 297. 



