680 



C. P. Whittingham, et al^ 



air. We have confirmed this in unpublished work and also investigated the 

 effect of increasing the O2 partial pressure on the photometabolism of glucose. 



Table III compares the effect of either 20% or 99-97 O2 on the photo- 

 metabolism of glucose by Chi ore 11a in the presence of 0.03% CO2. Increasing 

 the Op partial pressure greatly increases the activity in glycollate with a 

 corresponding decrease in that of sucrose, suggesting that an intermediate on 

 the normal pathway from glucose to sucrose can be oxidised to glycollate. In 

 other experiments increasing the partial pressure of O2 also resulted in a 

 decreased incorporation of glucose into ethanol insoluble canpounds, perhaps as 

 a direct effect of O2 on the formation of polysaccharides frcra sugar monoP. In 

 the dark there is negligible 2C compound production fron glucose-l'^C even in 

 the presence of oxygen or oxygen and INH. 



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c) Effect of isoniazid 



During photosynthesis at low CO2 tensions INH inhibits the conversion 



1 accumulation of 2-carbon compounds^ '^»°'' . 



of 



glycine to serine, leading to an 

 Table IV shows that INH has a sindlar effect on the 2-carbon compounds formed 

 during the photometabolism of glucose at COp tensions of 0.03% or less. In COp 

 free air more than 70% of the total 14c in the ethanol soluble fraction was 

 recovered in glycine and glycollate in the presence of the inhibitor. This 

 accumulation of 2-carbon compounds is accanpanied by a marked decrease in 

 activity in alanine, aspartate and malate. The effect of INH on the incorpora- 

 tion of activity into sucrose is variable, but there is a marked inhibition in 

 the presence of O2 and we have found a similar inhibition by INH of sucrose 

 labelled with ^^002 in the presence of 99.97% O2. 



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