1646 



CHEMICAL PATH OF CARBON DIOXIDE REDUCTION 



CHAP. 36 



activity appeared, however, in these compounds if the cells were allowed 

 to stand in the dark for a few minutes before killing. 



Utter and Wood (1951) criticized the identification of PGA as first photosynthetic 

 intermediate, suggesting that its tagging may be the result of an exchange, and not of a 

 net carboxylation. Fager and Rosenberg (1952) pointed out, in answer, that the quan- 

 titative correspondence between manometrically determined CO2 uptake and the 

 amount of C* found in PGA does not admit of such an interpretation. 



We will have to return to this finding, and the conclusions derived from 

 it as to the interaction between photosynthesis and respiration, later in this 

 chapter, and also in chapter 37D. 



4. The Experiments of the Chicago Group 



Before proceeding with a description of the further findings by the Cal- 

 vin group, made possible by paper chromatography {cf. sections 5-10), 

 we will describe work carried out in 1948-49 by Gaffron, Brown, Fager and 



to 

 o 



o 



o 



cc 

 a. 



O 



TIME, hours 



Fig. 36.5. Dark fixation of C* by 105 mL cells in 5 ml. phosphate buffer. CO2 

 exhausted by preillumination. No significant uptake of CO2 observed mano- 

 metrically (after Brown, Fager, and Gaffron 1949). 



Rosenberg in Chicago in which, like the above-described earlier Berkeley 

 studies, more common methods of chemical separation were used. Their 

 first results (1948, 1949) contrasted sharply mth the Berkeley findings ; in 

 particular, they found only insignificant amounts of phosphoglyceric acid 

 among the early products of photosynthesis. Subsequently, however 

 (1950S 1951), the role of phosphoglyceric acid as the most important early 

 product of photosynthetic C* fixation was confirmed at Chicago. 



