324 RADIATION BIOLOGY 



Clendenning and Ehrmantraut (1950) concluded that in their flashing- 

 light experiments the limiting catalyst must be assigned to a reaction 

 more closely connected with "the basic transformation of light energy 

 into chemical energy, e.g., the stabilizing reaction of Franck and Herz- 

 feld's catalyst B, or the energy-transferring reaction involving an inter- 

 mediate acceptor, as postulated by Dorrestein, Wassink, and Katz." 

 These studies, at least, clearly " support the view already arrived at, 

 namely, that dark processes are involved in the photochemical evolution 

 of oxygen from quinone. An additional interesting observation made 

 was that the Hill reaction showed no induction phenomena, irrespective 

 of the oxidant. Franck and Gaffron (1941) have ascribed the induction 

 phenomena to the presence of a natural narcotic. Clendenning and 

 Ehrmantraut (1950) were led to stress another view, namely, that a 

 limiting factor, e.g., lack of "carbon dioxide acceptor" after a dark period 

 and its gradual synthesis in Hght, might be the cause of the induction 

 phenomena. This would be in accordance with Calvin and Benson's 

 views (1948), with the recent conclusions reached by Eager et at. (1950), 

 and with the views reached by Wassink and coworkers from their com- 

 bined studies of photosynthesis and pigment fluorescence in algae and in 

 purple sulfur bacteria (see Wassink and Katz, 1939; Wassink et at., 1942; 

 Dorrestein et at., 1942; Wassink and Kersten, 1943-1945). In an exten- 

 sive discussion of the available kinetic work from various sources on 

 chlorophyll fluorescence and photosynthesis, Wassink (1951b) arrived at 

 the conclusion that Franck's views (1949) would be brought much nearer 

 to his own when the hypothetical "natural narcotics," which are postu- 

 lated to be produced in part by fermentation and in part by oxidation, 

 were replaced by the postulate of a "Hmiting factor." 



4-5. THE CONNECTION BETWEEN REDOX POTENTIALS 

 AND PHOTOSYNTHESIS 



The general concept of photosynthesis to which the combined studies 

 of fluorescence and gas exchange (Dorrestein et at., 1942) have led made 

 it worthwhile to investigate this connection. If a suspension of purple 

 sulfur bacteria, Chromatium, is illuminated, distinct shifts in the redox 

 potential are revealed if platinum electrodes in the suspension are brought 

 into connection with a reference electrode. It is interesting that these 

 shifts were shown to have a definite bearing upon the prevailing con- 

 ditions for photosynthesis (Fig. 5-15). Suspensions of Chromatium are 

 illuminated in phosphate bufi'er at pH 6.6 in N2 + II2, in N2 + H2 + CO2, 

 and in N2 + CO2, respectively. With the start of the illumination, 

 a potential shift toward the oxidized side is observed in all cases; it is 

 diff"erent, however, in magnitude, depending on the special conditions 

 (Wassink, 1947). It is smallest in N2 + H2, somewhat larger in N2 + 

 H2 + CO2, and largest in N2 + CO2. Gas exchange is negligibly small 



