226 



Donald L. Kelster 



measure the Hill reaction. It is this property of the dyes which 

 led previous investigators to believe that there was no ATP 

 formation coupled to their reduction and thus postulate by 

 necessity that the dyes intercept electrons at some point in the 

 electron transport chain prior to the site of phosphorylation. 



The uncoupling action of the dyes probably accounts for the 

 observations of Whittingham and Bishop'' ^\ who recently observed 

 that the time between flashes of light was considerably shorter 

 for optimum production of oxygen with DCI than with ferricyanide 

 as the electron acceptor. They suggested, therefore, that 

 production of oxygen by reduction of dye did not proceed through 

 the same thermal reaction (phosphorylation) required for ferri- 

 cyanide reduction. They also found that if the ferricyanide 

 reduction was uncoupled from phosphorylation by ammonium, ions , 

 the optimum time between flashes was of the same magnitude as 

 with DCI. Witt and coworkers ^'^'^ ^ observed that DCI accelerates 

 the decay of "Type 2" absorption increases at 515 my in chloro- 

 plasts. This decay is a thermochemical process, and it is likely 

 that the acceleration of decay can now be explained by the 

 uncoupling effect of the indophenols. 



It is of interest that Low et al. ^ ^^ have reported that 

 oxidized but not reduced DCI inhibited Pi-ATP exchange reactions 

 in rat liver mitochondria. 



Hill and V/alker'^^^ several years ago observed that, "The 

 phosphorylation reaction itself now appears as a part of normal 

 photochemically induced H-transfer." They also observed, 



"It does not follow. . .that all substances capable 

 of being reduced by illuminated chloroplasts prepara- 

 tions would be capable of initiating phosphorylation. 

 The coupling between reduction and phosphorylation 

 can be abolished and an active agent can become 

 inhibitory at higher concentrations so that affinities 

 relating to the chloroplast system have to be in a 

 suitable range." 



Contribution No. 13^^ of the Charles F. Kettering Research 

 Laboratory. 



