338 li. C. WAlSSIiNK 



be intercalated (line b). During this period, the fluorescence curves 

 are independent of CO2 and insensitive to CO2 reduction inhibitors 

 (6,10). This suggests, in addition to other phenomena mentioned 

 below, that phosphate is l)eing taken up into the photosynthetic chain 

 prior to CO2. Probably within the time of about 1 minute (cf. Strehler's 

 curve. Fig. 3) the EH (or F,GH) phosphate-compound formation 

 gives rise to an (energy-rich) phosphate pool, probably ultimately 

 filled mainly by ATP. 



Line (c) contains the interpretation of the experimental results 

 discussed above. The pool of organic, probably "energy-rich" phos- 

 phate is being continually refilled by the hght reaction, according to 

 lines (a) and (b). It is emptied, as far as our experiments go, along 

 three different pathways: (i) in the presence of CO2 the major part is 

 used along the pathway of CO2 reduction whereby it is reconverted 

 into inorganic phosphate, suggesting a decrease of the overall con- 

 version, which is measured; (ii) in the presence of sugar, an additional 

 pathway (which probably may be denoted mainly as "oxidative as- 

 similation") equally leads back to inorganic phosphate; (iii) when 

 both (i) and (ii) are curtailed the formation of polyphosphate is ob- 

 served, obviously resulting from "overfilling" of the organic phosphate 

 pool. 



The results underlying line (c) are strongly indicative of phosphate 

 fixation in the photosynthetic chain in fairly immediate sequence of 

 the light reaction, prior to the entrance of CO2. Otherwise it could not 

 well be explained how the absence of CO2 might lead to increased 

 polyphosphate formation. The underlying phosphate fbcation as such, 

 therefore, must be independent of COo reduction and get light- 

 dependent. The experimental results leading to this presentation were 

 among the earliest demonstrations of a true "photosynthetic phos- 

 phorylation" (1). 



Discussion 



Krall : In answer to the question whether Dr. Wassink's bound phosphate might 

 be the same as my compound 5a, I do not believe that to be the case. My 5a-5b 

 complex is the last compound in the phosphate pool to become labeled with P'^ 

 while Wassink's bound pliosphate is labeled easily. 



Benson: Do you think that the polyphosphate reservoir might be an energy 

 source? 



Wassink : We, of course, have l>een aware of this question and we have investi- 

 gated whether this reservoir can be emptied again. It appears that it (ran be 



