677 



C. P. Whittin^iani, et al. 



presence of isonlazidrO, glycolllc acid excretion; A, carbon 

 dioxide uptake. 



Fig. 2. The time course of l^^C incorporation into individual 

 conpounds of the ethanol-soluble fraction. 



high carbon dioxide concentration 

 low carbon dioxide concentration 



in the absence of isonlazid 



hi^ carbon dioxide concentration 

 low carbon dioxide concentration 



in the presence of isonlazid 



We have found (2,6) that the drug Isonlcotinyl hydrazlde has a marked effect 

 on the products of but not the rate of photosynthesis in Chlorella . Its use 

 results in a 250^ increase in glycollate production for the same CO2 uptake 

 (Table I). -'•^COg studies show that an equal amount of glycine is produced 

 (Fig. 2), and if both carbon atoms of glycollate and glycine are supplied by 

 the CO2 they would together equal 1/2 of the total CO2 uptake. This accumula- 

 tion of 2 carbon conpounds in the presence of INH results from blocking the 

 conversion of glycine to serine and subsequent products, e.g., alanine, 

 aspartate and malate (see Figs. 2 and 3). 



T^le I. Effect of isonlazid concentration on the rate of 

 photosynthesis and glycollate excretion. 



Isonlazid concentration 



Rate of photosynthesis 

 ul CO2/UI cellsAir 



Rate of glycollate excretion 

 ug/glycollate/ul cellsAir 





 10-^ M 

 10-3 M 

 10-2 ivi 



2.77 

 2.62 

 3.42 

 3.13 



0.435 

 0.772 

 0.830 

 1.26 



It is believed that (at low CO2) serine is converted to aspartate and malate 

 via phosphoenol pyruvate for the following reasons: inhibition by INH of I4c02 

 incorporation into malate and aspartate can be observed within 5 sec of 

 exposure to l^cop and before glycollate and glycine are active. This activity 

 in aspartate and malate is largely confined to the Ci^ position in the controls, 

 but on the other hand INH does not inhibit dark j'-^C02 fixation into aspartate 

 and malate, incorporation of the activity from l^c glucose into aspartate and 

 malate, or PEP carboxylase in vitro . 



The derivaticai of the carbon skeletons of glycollate and glycine from inter- 

 mediates of the carbon reduction cycle was shown by an experiment in which the 

 ethanol soluble coipoyinds of Chlorella were labelled during photosynthesis in 

 0.1^ CO2 containing -"-^COp. After 5 rain the l4co2 was replaced by ■'■2c02, and 

 the subsequent changes in the intermediates are shown in Fig. 3- 



The intennediates may be divided into 3 classes: 1) substances in which the 

 radioactivity decreased rapidly, e.g., PGA, sugar monophosphates and diphos- 

 phates; 2) substances showing initially a slight increase or steady level of 

 l^c subsequent to the change and then decreasing. This group contains all the 

 amino acids; 3) substances which continued to increase in l^c content, e.g., 

 sucrose and glycollate, the latter being excreted into the medium. 



The change in concentration of various intermediates in a period of darkness 

 inmediately following photosynthesis was also investi^ted. When the light was 

 turned off the intermediates of the photosynthesis cycle were converted to PGA 



