CONCENTRATION OF INHIBITORS 



955 



tribution of its effect to a difference in the activity of HCN molecules and 

 CN- ions (c/. Vol. I, page 301) doubtful. Figure 27.1GB shows that photo- 

 s}Tithesis of Nitzschia is half-inhi])ited by about 1.5 X 10"^% or about 2 X 

 10-5 mole/1. KCN. For similar figures for Chlorella, Hormidium and other 

 algae, see Table 12. V (Vol. I, page 305). 



The effect of cyanide on the stea,dy fluorescence of Chromatium is shown 

 in figure 28.45. It is somewhat complex, but, in general, amounts to an 



lO . 



E 



o 

 o 



< 



Q. 



Z3 



E 

 E 



O 



o 



UJ 



< 



I- 



Q- 



3 



300 



250 



200 



0.005 0.010 0.015 



KCN CONCENTRATION, % 



0.020 



0.003 0.006 0.008 



KCN CONCENTRATION. % 



Fig. 27.16. (A) Effect of cyanide on carbon dioxide reduction by Chromatmm in 

 thiosulfate (1% solution) and hydrogen (15%) (after Wassink, Katz and Dorrestein 

 1942). {B) Effect of cyanide on carbon dioxide reduction and respiration of Nitzchia 

 (after Wassink and Kersten 1944). 



increase of F at the lower light intensities, and a decrease at the higher light 

 intensities, and is thus reminiscent of the effect of carbon dioxide starvation 

 (c/. fig. 28.30A and B). The analogy is supported by the observation that 

 [KCN], like [CO2], has no effect on F in the absence of reductants (except 

 for concentrations ^ 0.01% KCN, where the fluorescence becomes strongly 

 depressed ; complete suppression of carbon dioxide reduction occurs much 

 earlier, at about 0.015% KCN. 



Hydroxylamine. In chapter 12 (Vol. I, page 311) we found that hy- 

 droxylamine is a strong poison, the mode of action of which is rather com- 

 plex. While it affects pai'ticularly strongly the oxygen-liberating process 



