C5 AND Ct sugars AS INTERMEDIATES 



1671 



and more specifically, as ribulose, by co-chromatographing with the pure 

 compound. 



Table 36. VI shows the relative amounts of the several tagged sugar 

 phosphates found after 1 to 20 min. photosynthesis in C*02 in different 

 organisms. 



Table 36.VI 



Relativj: Amounts of Different Phospiiorylated Sugars after Short Period of 



Steauy-State Photosynthesis in C*02 (after Benson et al. 1952) 



Duration 

 of PS in 

 Organism C*02 (min.) 



Rhodospir ilium ruhruni 20 



Scenedesmus (1 day old). ... 5 



Chlorella 1 



Barley seedling leaves 1 



Soy bean leaves 5 



In discussing these findings, Benson et al. noted that sedoheptulose ac- 

 cumulation is known to occur during the photosynthesis of certain succu- 

 lents. The same sugar (or its phosphate) was also identified in many other 

 plants. Ribulose, on the other hand, is not known as a constituent of 

 plants, although the corresponding aldose (ribose) is known to occur in 

 them. Ribulose phosphate has been previously observed in bacteria, but 

 not in photosynthesizing organisms. 



Bassham, Benson, Kay, Harris, Wilson and Calvin (1954) inquired into 

 the distribution of labelled carbon in the ribulose and sedoheptulose skele- 

 ton after brief periods of steady photosynthesis in 0*02," exposures as 

 short as 0.4 sec. were used in this work. A suspension of Scenedesmus 

 ohliquus was placed in a rectangular reservoir traversed by a stream of air 

 charged with 4% CO2. The steadily photosynthesizing suspension was 

 pumped out of this reservoir through a transparent tube. At a certain 

 point in the tube, a solution of C*02 was injected into the suspension. The 

 mixture was then discharged into boiling methanol. The time of exposure 

 to C*02 in light (between injection and discharge) could be varied by chang- 

 ing the rate of pumping; the illumination was about 40 klux from each side. 



Table 36.VII shows the distribution of C(14) in C3, Ce, C- and C5 

 chains formed after 5.4 see. or steady-state photosynthesis of Scenedesmus 

 in C*02. 



Table 36. VII indicates clearly that the Ce chain is formed bj^ head-to- 

 head condensation of two C3 chains. The mechanism of formation of the 

 C7 and C5 sugars is less obvious; the suggested interpretation will be dis- 

 cussed in section 12 below. 



