ON THE COUPLING OF PHOTOPHOSPHORYLATION TO ELECTRON TRANSPORT 



Mordhay Avron and Noun Shavit 



Introduction 



The large increase in the rote of electron transport brought about by the addition of the 

 components necessary for phosphorylation was first demonstrated in 1958 with ferricyonide 

 as an electron acceptor(l/ 2). |t has since been extended to include the other common 

 electron acceptors in photophosphorylation, NADP(3) and indophenol dyes('^), and studied 

 in detailV^' ' '. A similar and normally somewhat larger increase in the rate of electron 

 flow can also be brought about by uncoupling the chloroplosts from the control of the 

 accompanying phosphorylation. This type of effect results in a concomitant large increase 

 in the rate of electron transport and large decrease in the rate of ATP production. The 

 first demonstration of uncoupling in chloroplosts was provided by Krogmann and Jagendorf\°'. 

 Irreversibly uncoupled chloroplosts were obtained by diluting chloroplosts at pH 6 in the 

 presence of a high concentration of salts. The first demonstration of an uncoupling agent 

 soon followed when ammonium salts were shown to reversibly uncouple photophosphorylation 

 at concentration around 10""^ M ^°), Good has further studied the phenomenon and 

 concluded that a number of monofunctional amines and several anions at high concentrations, 

 con act as uncouplers''^' "). 



Figure 1 illustrates the typical response of the reduction of ferricyonide and its accom- 

 panying phosphorylation to the addition of the components necessary for phosphorylation. 



■5 ^ {NoM9.flOP.ro»l 



CH, tIM) Ct Cor<er4fOI>oi 



Fig, 1. Uncoupling of the ferricyonide system by methylammonium chloride. 

 Reaction conditions and assays as previously described' ' '. Light 

 intensity, 160,000 lux; reaction time, 2 minutes; gas phase, air; tempera- 

 ture, 20°C; once washed chloroplosts containing 10-20 micrograms of chlo- 

 rophyll per ml. 



or of on uncoupler. It can be seen that the addition of the phosphorylation-components 



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