HILL REACTION AND ITS RELATIONSHIP TO PHOTOPHOSPHORYLATION 423 



TABLE I 

 Effect of CO^ and of Trichlorophenol Indophenol (TCP) on 



THE PhOTOREDUCTION OF FeRRICYANIDE 



Ferricyanide reduced 

 (;LimoIes/mg. chlorophyll/hr.) 



No CO2 i-sf'oCO. 



No TCP 73 93 



003 /imole TCP 107 240 



006 /tmole TCP 107 230 



o- 10 /imole TCP 88 204 



Reaction mixtures contain 100 /nmoles of pyrophosphate buffer of pH 6-8, and 

 spinach grana containing 02 mg. chlorophyll in a total volume of 3-0 ml. After 

 preincubation in the dark for 2 hrs., 20 /xmoles of ferricyanide were tipped in from 

 the side arm and the lights were turned on. T = 20 , 4000 ft. -candles white light. 

 Gas phase, either No (with KOH in centre well), or i s",, COo in No. 



tension on the Hill reaction rate with grana was the same as the effect of 

 COo tension on the rate of photosynthesis in the intact leaf. Twelve years 

 ago, Boyle [56] reported that COo was required for the photoreduction of 

 quinone. His findings have received little attention, presumably because 

 of his failure to define appropriate experimental conditions for duplicating 

 his results. 



The experiment summarized in Table I was one of a series carried out 

 to determine the optimal concentration of dye for demonstration of the 



TABLE II 

 Effect of CO., and pH on the Hh.l Reaction 



Initial pH 



COo Ferricyanide reduced 



(i-5"o) (/xmoles/mg. chlorophyll/hr.) 



6-8 - 72 



6-7 + 152 



67 + 173 



6-7 - 48 



6-6 



45 



The reaction mixtures contained 100 /tmoles of sodium pyrophosphate buffer, 

 initially of pH 6-8, 40 /xmoles of KCl, 0-07 /xmole of trichlorophenol indophenol, 

 and kohlrabi grana containing 0-2 mg. chlorophyll, with water to make a final 

 volume of 3 -o ml. HCl was added to adjust the pH in the absence of CO.,. The 

 dark preincubation was for 2-5 hr. 20 /itmoles of fi^rricyanide were tipped in from 

 the side arm at the onset of illumination with white light, 4000 ft. -candles. 

 Illumination was for 20 min. T — 20". 



