CHEMICAL KINETICS OF THE HILL RHACTIOM 



385 



111 this laboratory Rieske (4) has studied the effect of deuterium 

 oxide on the chloroplast Hill reaction as a f\uiction of pH and of light 

 intensity. The results are much more invoh'ed than those reported 

 for photosynthesis in that both tlu^ light and 1h(> dnik parameters are 



1.0 — 



0.5 



0.0 



T 



T 



0.4 



kL (D2O) 



0.2 



0.0 



5.5 



6.5 



7.5 



8.5 



pH 



Fig. 5. Curves showing the values of the rate parameters Ul and ko in HoO and 

 D2O for the Hill reaction of chloroplast fragments as defined by equation 2. The 

 pD values were estimated by the relation pD = pH (glass electrode) + 0.4. The 

 reaction was carried out in O.lil/ phosphate buffer with O.OOOSil/ ferricj^anide at 

 10°C. 



decreased by deuterium oxide and that the pattern of pH dependence 

 described above becomes even more complicated. The pattern ot 

 /co and l-L behavior in H2O and D2O (Fig. 5) resembles that reported by 

 Horwitz (11), in so far as comparison is possible. The inhibitory effect 

 on Ud is progressive and only slightly if at all reversible. Within a 

 small experimental error the activation energy of the Hill reaction at 



