958 



CONCENTRATION FACTORS 



CHAP. 27 



Sodium azide. Only one casual observation of the inhibition of photo- 

 synthesis by azide was mentioned in Volume I (page 318). Since then, the 

 effect of this tyi:)ical poison for heavy metal catalysts on the gas exchange 

 and fluorescence of Chromatiurn has been studied quantitatively by Was- 

 sink, Katz and Dorrestein (1942). Figures 27.18A and 27.18 B show the 

 rates of photoreduction, with molecular hydrogen and thiosulfate, respec- 

 tively, as functions of azide concentration. The half-inhibiting concentra- 

 tion is about 0.02% sodium azide with hydrogen and about 0.01% with 

 thiosulfate as reductant. Strangely enough, particularly strong inhibition 

 was found in weak light (fig. 28.1 ID). 



o 



< 



CL 



3 



700 



600- 



500 



400 



300 



200 



as 10 15 20 2.5 3.0 

 ETHYLURETHAN CONCENTRATION, % 



Fig. 27.19. Effect of ethylurethan on photoreduction of 

 carbon dioxide in Chromatiurn (after Wassink, Katz and 

 Dorrestein 1942): 5% CO2; 15% H2; pH 7.6; 29° C; strong 

 light. 



The effect of azide on fluorescence also was different from that of the 

 other enzyme poisons, such as cyanide and hydroxylamine. In the first 

 place, fluorescence was strongly affected even in the absence of reductants 

 (fig. 28.47A). In the second place, the typical effect was a considerable 

 lowering of the yield of fluorescence, particularly at the higher light intensi- 

 ties (fig. 28.47B). 



All three observations (inhibition of the gas exchange at low light in- 

 tensities, effect on fluorescence in absence of reductants, lowering of fluores- 



