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Donald L. Kelster 



form. Under these conditions ATP formation was observed to 

 accompany cytochrome c reduction with an ATP:2e- ratio that 

 approached 1.0 at low TCI concentrations (3 x 10"°M). 



INDOPHENOLS AS UNCOUPLERS OF PHOTOPHOSPHORYLATION 



Fig. 1 also illustrates the uncoupling effect of TCI. As the 

 TCI concentration was increased the rate of cytochrome £ reduction 

 was stimulated while ATP formation was Inhibited until at 

 2.5 X 10"5m TCI, very little ATP synthesis occurred. This 

 clearly demonstrates the uncoupling effect of the oxidized 

 indophenols. A further demonstration of this uncoupling effect 

 is illustrated in Fig. 2 which shows the inhibition of cyclic 

 photophosphorylation by TCI. This experiment was performed under 

 argon in the presence of 10~5m £_-chlorophenyl-l ,1-dimethylurea 

 (CMU) to inhibit dye reduction and thus maintain the TCI in its 

 oxidized form. Under these conditions, TCI increasingly inhibits 

 cyclic phosphorylation with almost complete inhibition by 10 M 

 TCI. The curve labelled "reduced TCI" (Fig. 2) demonstrates that 

 the reduced form of the dye has no inhibiting effect. Avron and 

 Jagendorf^^^) first observed the inhibition of cyclic phosphoryla- 

 tion by TCI but at that time concluded that the dye was interfer- 

 ing with electron transport reactions rather than uncoupling or 

 inhibiting phosphate transfers. 



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2 4 6 8 



TCIP CONCENTRATION MkIO' 



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Fig. 2. The inhibition of cyclic phosphorylation by TCI. 

 The reaction mixture, pH 8.2, contained 0.06 ymole pyocyanin, 

 0.03 umole CMU, and 22 ug chlorophyll In addition to those 

 described. The reaction was run in Warburg vessels with 

 pyocyanin, TCI, and CMU being tipped in after flushing for 

 10 min with argon. The control rate of phosphorylation 

 during a 6 min illumination period with pyocyanin alone 

 was 21i) umoles/mg/hr which was inhibited 20?5 by CMU. 



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