APPLICATION OF PAPER CHROMATOGRAPHY 1655 



the cells are killed.) If C*02 is added only at the moment when the light 

 is switched off, the loose complex A.CO2 is not tagged, and C*02 can be taken 

 up into this complex, in the subsequent dark period, only by exchange, in 

 competition with the stabilization reaction A.CO2 -^ ACO2; the uptake is 

 correspondingly smaller. 



This interpretation implies that the C*02 "pick-up" in fig. 36.12 means 

 no true {i. e., manometrically measurable) absorption of carbon dioxide. 

 In Volume I, chapters (section B4) and in chapter 33 (section A3), evidence 

 of a net pick-up of C02-gas after the end of photosynthesis has been pre- 

 sented (McAlister, Aufdemgarten, van der Veen). Its volume (about one 

 molecule CO2 per molecule chlorophyll, equivalent to about 20 sec. of maxi- 

 mum photosynthetic C02-uptake) and its time requirement (about 20 sec.) 

 were about the same as described by Gaffron et al. for the radiometrically 

 determined C*02 pick-up. True, McAlister and Myers found no measur- 

 able pick-up when the CO2 concentration was high (as it has been in Gaf- 

 fron's experiments) ; nevertheless, the apparent equality in the rate of the 

 two processes seems to argue against the assumption that one of them repre- 

 sents a combination of free acceptor A Avith CO2, and the other, stabiliza- 

 tion of A.CO2 to ACO2. 



At subsaturating light intensities, the amount of postphotosynthetic 

 C*02 pick-up is reduced proportionally, remaining approximately equiva- 

 lent to the CO2 uptake in 10 sec. in light (c/. bars h-k in fig. 36.12). 



Bars D and F in the fig. 36.12 insert show that the postphotosynthetic 

 C*02 pick-up leads to a distribution which is markedly different from that 

 observed by Gaffron et al. after preillumination without CO2 (fig. 36.11): 

 25% of the tracer in D, and >50% of it in F, are located in compounds 

 other than PGA and PA. This observation, too, remains in need of inter- 

 pretation. Perhaps an explanation could be based on the difference be- 

 tween cells filled with abundant intermediates of photosynthesis and cells 

 bare of such intermediates. 



Observations of the type shown in fig. 36.22, revealing changes in the 

 distribution of C* within the cells immediately after the end of illumination, 

 are obviously relevant to the pick-up phenomena, whether observed 

 analytically (chapters 8 and 33) or noted radiometrically. 



5. Early Intermediates Other Than PGA; Paper Chromatography 



A most important step forward was made in 1948 by application, to the 

 problem of carbon dioxide reduction intermediates, of a new chromato- 

 graphic technique : paper chromatography. To combine this method (de- 

 veloped by Consden, Gordon and Martin in England in 1944) with the 

 radioactive tracer technique in the study of photosynthesis was first sug- 

 gested by Fink and Fink (1947). Calvin and co-workers found this 

 combination particularly suitable for rapid fractionation and identification 



