rONCENTRATION OF INHIBITORS 



057 



reduction by adapted Scenedesmus, no drop below 50% at any concentra- 

 tion up to 3 X 10-- mole/l.; photoreduction by Chrornatium, 50% inhil)i- 

 tion at 3 X 10-^ mole/l., {cf. fig. 27.17). In experiments with bacteria 

 (in contrast to those of Weller and Franck, 1941, on Chlorella; cf. Vol. I, 

 ]mge 312) no inhibition by hydroxylamine was found in weak light (cf. 

 fig. 28.110 and fig. 28 in Vol. I). The difference is understandable if the 

 effect of hydroxylamine on photosynthesis in weak light is due to its action 

 on the oxygen-liberating enz^^me (designated as Eo or Ec in Vol. I); a 

 possible "autocatalytic" mechanism of this effect was discussed on p. 312. 



600 - 



500 



400 



200- 



150 



IB) 



E 

 E 



OJ 



X 

 + 

 eg 

 O 

 O 



li. 300- 



o 



< 



I- 



200 



6 

 £ 



O 

 O 



< 



I- 



a 



3 



100 



50 



-50 



-100 



\ 



Scale of concentration 

 \ 10 times enlarged 



\ 

 \ 

 \ 



\. 



\ 



^^- 



\. 



0.1 0.2 0.3 0,4 0.5 

 NaNj CONCENTRATION, % 



1 02 0.3 04 05 

 NaNj CONCENTRATION,"/, 



Fig. 27.18. Influence of sodium azide on rate of photoreduction of carbon 

 dioxide by Chrornatium (after Wassink, Katz and Dorrestein 1942): (A) 15% 

 hydrogen; (i5) 1% thiosulfate. 5% CO.; pH 6.3; 29° C; strong light. 



In the absence of reductants, hydroxylamine hydrochloride was found 

 to have no effect on the fluorescence of Chrornatium, up to a concentration 

 of 0.5%. In the presence of reductants, hydroxylamine causes, in general, 

 an increase in the intensity of fluorescence; however, this effect becomes 

 marked only above 0.05%, while the reduction of carbon dioxide is half 

 inhibited by as little as 0.03% of the poison (cf. fig. 28.46). Thus, the 

 inhibition of bacterial photosynthesis by hydroxjdamine also seems to be a 

 complex phenomenon, the first stage of which has no effect on fluorescence, 

 ■\yhile the second stage causes an increase in the fluorescence yield. 



