EFFECT OF CATALYST POISONS 



1907 



in 5 X 10~2 M NaF lead to marked inhibition; a similar treatment with 

 6.7 X 10-"^ M NaF produced a 75% inhibition, while with 10 X 10"^ ilf 

 NaF photosynthesis was replaced by photoxidation. Potassium fluoride 

 had the same effect as sodium fluoride. The effect was stronger at the lower 

 pH values— probably because of easier penetration through the cell mem- 

 brane of neutral hydrogen fluoride molecules. The fluoride effect was 

 considerably weaker (but still noticeable) at 1.3 klux. Respiration was not 

 affected at all by fluoride in the concentrations used. 



m/750 lAA 



m/3000 lAA 



X no lAA 



Fig. 37D.8A. Inhibition of photosynthesis and respiration in Chlorella by iodoacetic 

 acid (lAA) (after Holzer 1954). 25° C, 18 mg. algae (dry weight) in vessel. Citrate 

 buffer pH 5.4; 1 % CO2 in gas phase (Pardee buffer in side tube). 



Simonis compared the effect of fluoride with the known inhibitions 

 of photosynthesis by iodoacetate and azide (c/. p. 318, and below) which, 

 too, are known to inhibit the formation of high energy phosphate esters. 

 However, he recognized that the experiments do not prove that the ob- 

 served (slow and only partially reversible) effect is due to direct inhibition 

 of a photosynthetic enzyme. 



The inhibition of respiration and photosynthesis of Chlorella by fluoride 

 was investigated by Holzer (1954). The effect on both processes was 



