ANDRE T. ] AGENDO 111 AND GIORC.IO lORTl 



581 



H 



CD 80 



- 60 



bJ 40 

 U 



Ld 20 



10 



-7 



PHOSPHORYLATION 



WITH 



PHENAZINE 



M ETHOSULFATE 



CMU CONCENTRATION 



Fig. 2. Inhibition of PMS-mediated phosphorylation by CMU under different 

 reaction conditions. All reactions are micro-aerobic and without ascorbate unless 

 otherwise indicated. Other conditions are described under Table 1 and Fig. 1. 

 The curves represent the average percentage of inhibition found in from 6 to 14 

 experiments. Vertical lines represent twice the standard deviation. When present, 

 10 jamoles of ascorbate were used in 1.5 ml final volume. Red, white, color of 

 incident light. ASC, ascorbate. 



The explanation in terms of the reaction sequence Hsted above 

 again becomes fairly obvious. Inhibition, as with pyocyanine, is due 

 to a combination of reaction 3 inhibited by CMU, and oxygen (re- 

 action 5) destroying the PMS reduced by the chloroplasts, and thus 

 eliminating the substrate for reaction 4. Reducing PMS non-enzymati- 

 cally will restore the substrate for reaction 4, and thus permit the 

 entire sequence 1, 2, and 4 to continue. 



At this point it is possible to indicate a remarkable similarity be- 

 tween chloroplasts poisoned by CMU and bacterial chromatophores. 

 In Chromatium, for instance, the phosphorylation by isolated 

 chromatophores is poisoned by small amounts of oxygen (10, 24) . 

 The poisoning can be overcome by adding substrates that serve as 

 electron donors. Similarly in CMU-treated chloroplasts, the pyo- 

 cyanine- and PMS-supported phosphorylations are poisoned by small 

 amounts of oxygen, and adding electrons from outside the system 

 through PMS restores the phosphorylation. Bacteria are constitu- 



