222 



Donald L. Keister 



Shen et al. ^^^ have also concluded that the indophenols are 

 uncouplers of phosphorylation from two types of experiments. 

 They have previously shown that ATP formation and light-induced 

 electron transport could be separated by pre-illuminating chloro- 

 plasts in the presence of phenazine methosulfate (PMS) but 

 without AD? and Pi. After a short but intense illumination, the 

 addition of ADP and 32pi results in the formation of ATP^-^^-". 

 When increasing concentrations of DCI was added along with the 

 ADP and Pi, the ATP formation was inhibited up to 85% by 10" M 

 DCI while the reduced dye had no effect. This type of inhibition 

 was interpreted as uncoupling. In addition they have measured 

 ATP formation and electron transport by chloroplasts in a system 

 containing both DCI and ferricyanide. With only ferricyanide 

 present an ATP:2e~ ratio of 1.26 was measured. With increasing 

 concentrations of DCI the ratio decreased until complete inhibi- 

 tion of ATP formation was observed with lO'^'M DCI. Ferricyanide 

 reduction was stimulated 25% by this concentration of dye. 



Fig. 3 illustrates this uncoupling effect of both DCI and TCI 

 on ferricyanide coupled photophosphorylation. Complete uncoupling 

 was observed with 7 x 10-°M TCI while almost a ten-fold higher 

 concentration of DCI was required for complete uncoupling. 

 3'-chloroindophenol was also shown to be an uncoupler at higher 

 concent rat ions . 



^©DCI 



'-a 



ZxlO-^M 

 



4 1 10"= M 



X 6.7xI0-5m 

 ^.-^J ©- 



2 4 6 8 



CONCENTRATION, M X 10' 



2 3 4 

 MINUTES 



Fig. 3. ( 



ferricyan 

 mixture , 

 and 100 u 

 in method 

 Fig. n. ( 

 formation 

 1.23 X 10 

 those des 

 samples w 

 TCI reduc 



Left) The uncounline effect of indophenols on 

 ide coupled phosphorylation. The reaction 

 pK B.O, contained ? umoles of ferricyanide 

 g chlorophyll in addition to those described 

 s. 



Right) The time course of TCI reduction and ATP 

 . The reaction mixture, pH 8.0, contained 

 "'^M TCI and 112 ug chlorophyll in addition to 

 cribed in methods per 3 ml of solution. One ml 

 ere removed for measurement of J'^Pi uptake and 

 t ion . 



