CHEMICAL KINETICS OF THE HILL REACTION 



381 



5 X 10~^ to 10~' M several complicating effects appear. As shown in 

 some detail for quinone in Fig. 3, the rate of the limiting light reaction 

 (fci) decreases rapidly and approaches zero as the oxidant concen- 

 tration exceeds IQ-- M. The rate of the limiting dark reaction {ko), 

 on the other hand, rises to a maximum at a concentration of slightly 

 less than 10"- M, after which it decreases rapidly. This same general 



LOG QUINONE MOLARITY 



Fig. '.'). Curves showing the relation between oxidant concentration and the rela- 

 tive values of the light-reaction-rate parameter k'L and the dark-reaction-ratc 

 parameter ko for the Hill reaction of isolated chloroplasts as defined by equation 2. 

 The reaction was measured manometrically with benzoquinone as the oxidant. 



behavior was shown by all the oxidants studied, though there are dis- 

 tinct quantitative differences. Studies in this concentration range 

 are also complicated by the so-called chloride effect (6). We have found 

 in this laboratory that the relative activating effect of oxidant con- 

 centration on ko is dependent on the chloride ion concentration of the 

 reaction system. These complications may be of some importance in 



