INHIBITION BY HYDROXYLAMINE 



313 



cyanide (the "carboxylase," Ea), but the oxygen-liberating enzyme 

 (Ec or £"0); and that the Umitation imposed on the over-all process by 

 the inactivation of this enzyme is lower the weaker the illumination, thus 

 leading to the same relative inhibition of photosynthesis in strong and 

 in weak light. According to this concept, the effect of hydroxylamine is 

 an indefinite extension of the state which usually prevails only during the 

 "short induction period" (i. e., in the first 2-5 minutes of illumination). 



Weller and Franck found that hydroxylamine reduces the oxygen 

 yield per flash in flashing light in a constant proportion, independently 

 of length of the dark intervals between flashes (while cyanide causes a 

 characteristic change in the shape of the flash jdeld vs. dark interval curve; 

 cf. p. 307 and Vol. II, Chapter 34). This observation is in agreement with 

 the assumption that these poisons act on two different enzymes. 



It was mentioned above that the hydrogen-adapted algae are com- 

 paratively insensitive to hydroxylamine. The capacity for adaptation is 

 reduced by hydroxylamine to the same extent as normal photosynthesis; 

 but if hydroxylamine is added after adaptation, it has only a very slight 

 effect not only on photoreduction, but also on the oxyhydrogen reaction 

 (and a somewhat stronger one on the coupled reduction of carbon dioxide). 

 The most striking effect of larger quantities of hydroxylamine is the 

 prevention of de-adaptation. As shown by figure 29, 10~^ m./l. NH2OH 

 prevents photochemical de-adaptation even at 6000 lux. 



1^" 



E 

 \ 



E 



E 



-5 - 



171 



c 

 O 



-10 



61 

 a 



o 

 a. 



10 15 20 



Time, minutes 



25 



30 



Fig. 29. — Protection of the hydrogen-adapted state in Scenedesmus by hydroxyl- 

 amine against re-adaptation by strong light (6300 lux) (after Gaffron 1942). Curve I: 

 no inhibitor. Curve II: 1 X lO'^ m./l. NHoQH-HCl. 



According to Gaffron (1942, 1944), the effects of hydroxylamine on 

 adapted algae can best be understood if one assumes that this poison 

 affects both reactions which lead from the primary oxidation product to 



