679 



C. P. I'/hittingham, et al. 



In unpublished experiments we have found that the addition of ATP and ribose- 

 5-phosphate to Chlorella cell brei in the dark results in ^^C02 fixation into 

 PGA, phosphoenol pyruvate, alanine, aspartate and glutamate. In both the 

 above experiments negligible amounts of activity were found in glycollate, 

 glycine and serine. INH did not affect these results, confirming that there 

 is no major flow of carbon through these corrpounds in the dark as there is in 

 the light. 



PHOTOrCTABOLISM OF GLUCOSE 



a) Effect of partial pressures of carbon dioxide 



Ihe distribution of activity in the various intemiedlates following addition 

 to Chlorella of a constant amount of uniformly labelled -'-^C glucose is sum- 

 marized in Table II. The results show: 1) a progressively slower utilisation 

 of glucose at the higher concentration of CO2; 2) a faster movement of radio- 

 activity through the photosynthetic cycle intermediates (the sugar diphosphates 

 and a large part of the sugar monophosphates) suggesting that the photosyn- 

 thetic cycle rotates at a higher speed at higher concentrations of COp; and 

 3) that as the cycle intermediates lose their activity with time, it appears 

 in two sets of conpounds. At low concentrations of CO2 the decrease is 

 largely accounted for by the increase in 2C conpounds and their derivatives. 

 (We regard aspartate, malate and alanine as largely derived from 2C compounds, 

 at least at the Icwer CO2 tensions, since their formation is inhibited by INH — 

 see belcw.) At higher COp concentrations this formation of 2C compounds is 

 decreased, and most of the activity lost from the cycle foms sucrose. 

 Dependence of sucrose formation on CO2 tension would not be expected if there 

 was a direct conversion of glucose to sucrose, and this suggests the latter has 

 been formed via the carbon reduction cycle. 



Table II. Effect of partial pressure of CO2 on photoassimilation 

 of glucose. All figures are approximations based on 

 counts applied to the chromatograms minus the counted 



b) Effect of Op partial pressure on the photanetabolism of glucose 



Previous workers(°'9,10) Yiave shown that photosynthetic glycollate produc- 

 tion by Chlorella is increased by partial pressures of O2 greater than that in 



