302 



CATALYST POISONS AND NARCOTICS 



CHAP. 12 



from 10~^ to 10~^ m./l. of cyanide will completely paralyze the photo- 

 synthesis of Chlorella, but will leave respiration unaffected or even 

 stimulated. 



Warburg (1919, 1920) found, and other observers confirmed, that 

 photosynthesis in weak light is indifferent to cyanide (cf. Table 12.1 and 

 Fig. 27), showing that cyanide does not interfere with the photochemical 

 process proper but affects an enzymatic "bottleneck" reaction which 

 limits the rate of the over-all process in poisoned cells in strong light. 



200 



150 



E 

 E 



!I00 





O 50 



o 



• w 



50 100 150 '10* 



intensity, ergs/cm. /sec. 



Fig. 27. — Effect of cyanide on photosynthesis of Chlorella at different light inten- 

 sities (after Wassink, Vermeulen, Reman, and Katz 1938). o: not inhibited; •: inhib- 

 ited by 0.05 ml. of 0.03% KCN per ml., corresponding to about 1 X IQ-^ m./l. 



Warburg (1920) made another interesting observation — that cyanide 

 reduces photosynthesis only to the compensation point (where the net 

 gas exchange is zero) but leaves unaffected the fraction of photosynthesis 

 which merely compensates for respiration (cf. Table 12.11). 



The last column in table 12.11 shows a "residual photosynthesis" 

 which is unaffected by 0.8 X 10"' m./l. of cyanide. These experiments 

 were carried out in very dilute carbon dioxide, so that the rate of photo- 

 synthesis in the noninhibited state was very small, and the existence of 

 a cyanide-indifferent residual photosynthesis could be demonstrated most 

 strikingly. However, Warburg gave table 12. Ill as a proof that cyanide- 

 resistant residual photosynthesis exists also under the conditions of 

 abundant carbon dioxide supply. The proof lies in thfe fact that none 



