613 



Mordhay Avron and Noun Shavit 



described to-date. The CCP derivatives are also the only group which uncouple both 

 oxidative phosphorylation and photophosphorylation at similar very low concentrations. 



Chlorpromazine has been shown by Low('°) to inhibit both electron flow and phosphory- 

 lation in oxidative phosphorylation, and by Wessels and Baltscheffsky to inhibit photophos- 

 phorylation(l '*). Figure 3 shows that it also exhibited all the usual effects of an uncoupler. 

 Pretreating chloroplasts in ethylenediaminetetraacetate (EDTA) in the absence of salts 

 has recently been found in our laboratory to uncouple them (Fig. 3) by releasing from tbem 

 o coupling factor(20)_ Under appropriate conditions this coupling factor can be recom- 



- 50 

 I 



Fig. 3. Uncoupling of the ferricyanide system by chlorpromazine, or by 

 pretreatment of the chloroplasts with ethylenediaminetetraacetate (EDTA) . 

 Details as in Fig. 1; pretreatment in EDTA consisted of suspending chloro- 

 plast fragments for the time indicated in IxlO""* M EDTA follov/ed by on 

 immediate assay in the various photoreactions. 



bined v/ith the uncoupled chloroplasts resulting in a partial restoration of coupled phos- 

 phorylation. 



Differential effects of uncouplers on several photoreactions 



One unusual property of some of the uncoupling agents described is shown in Fig. 4. 

 In this figure v/e compare the effect of three uncouplers on two types of photophosphory- 

 lation: that dependent upon the presence of phenazine methosulfate (RMS) and that 



■ FERRIC TON) Oe 



3.IO 3.10 



UNCOlFieR CO«C£NT«»TIO«< - M 



Fig. 4. Differential effect of several uncouplers on phenazine methosulfate 

 (PMS) and ferricyanide dependent photophosphoryiations. 

 Details as described under Fig. 1. 



