CHEMirVL KINKTICS OF TIIK HILI, in:A( TIOX 



38M 



quinoiic, (li('hl()ro(|iiiiioiK', phlliiocol, 4-methyl iiuphthofiuiiioiie, and 

 other vitamin K analogs, etc., were good a('ce[)t()is, while ferricyanide 

 eoiild be studied at concentrations as low as 10 ^ M. A number of 

 compounds of theoretical interest, such as (i-thioctic acid, 5-thioctic 

 acid, and glutathione, did not function as direct electron acceptors in 

 our experiments. 



HYDROGEN ION DEPENDENCE OF THE HILL REACTION 



Robin Hill, in his original work, pointed out the great dependence 

 of the reaction rate on the pH of the suspending medium. Photo- 



— 0.4 



0.2 



_ 0.0 



7. 



7.5 



8.0 



PH 



Fig. 4. Ciu'ves showing the relation between pH and the relative values of 

 JiL and ko for the Hill reaction of isolated chloroplasts as defined by ecjiiation 2. 

 The reaction was run at eight light intensities and the reaction rates were deter- 

 mined by the potent iometric method (2). The reaction was carried out in O.LI/ 

 potassium phosphate buffer. 



synthesis in living cells is much less sensitive to the hydrogen-ion 

 concentration of the supporting fluid, probably because of the pres- 

 ence of pH-regulating mechanisms. It is likely that detailed studies 



