KINETICS 



1601 



optimum at pH 7.0; the rate depended, however, not only on the pR, but 

 also on the chemical nature of the buffer. It was higher in 0.4 M sodium 

 sorbitol borate buffer than in 0.04 Af sodium or potassium phosphate buffer, 

 although the pH was the same (7.0) in both cases. 



Gorham and Clendenning (1952) found that the pH effect depends 

 strongly on the presence of chloride (figure 35.22E). 



1200 



800 



400 



O 



1200 



800- 



400 



0-5 MIN. 



I0°C, 



\ WITHOUT 



\ 



\ 



20°C. 



8.0 



1200 



800 



400 





 1200 



800 



400 





 H 



5-IOMIN. 



IO°C. 



X 



fj^\. WITH 



\ 



KCL 



/^ 



^ 



WITHOUT 

 KCL 



20°G. 



.y^"^' 



/^ 



Fig. 35.22E. Effect of joH on photochemical activity of washed, frozen and 

 thawed chloroplasts in Hill's mixture, with and without 10"'' M KCl (Gorham and 

 Clendenning 1952). 0.78 mg. Chi per vessel. 



With ferricyanide alone, Spikes, Lumry, Eyring and WajTynen (1950) 

 found (by redox potentiometry) an optimum at pH 6.85, with sharp de- 

 cline of the rate to almost zero at pH < 5 or > 7.5. 



With quinone, Warburg and Liittgens (1946) gave pH 6.2-6.5 as opti- 

 mum, the rate declining to zero at pH 7.0; Amon and Whatley (1949), on 

 the other hand, gave pR 7.0 at 10-15° C, and pB. 7.6, at 3° C. as pH 

 optima for the same oxidant. 



