608 



Jagendorf and Hind 



Figure k, pH shift induced by actinic illumination. 

 Chloroplasts were resuspended in .01 m NaCl and washed 

 once. 2 mg of chlorophyll were used in total vol. of 

 10 ml, of 10 mM NaCl in a water- jacketed cell at C. 

 Pyocyanine .05 mM when used. Note the electrode response 

 to light, opposite in direction to the pH shift caused 

 by the chloroplasts. Reaction mixture was at pH 6.3* 

 without addition of buffer. 



This rise in pH in the light is readily reversible in 

 the dark; is much greater at pH 6 than at pH 8 and is 

 both larger and very much faster when pyocyanine is 

 present than when it is absent. Thus far it correlates 

 quite well with both the kinetics of the intermediate 

 X , and the non-specific changes in optical density. 



By using a pH-stat to titrate the chloroplasts with 

 acid, the proton uptake (or hydroxyl excretion) can be 

 quantitated. The amount of acid was found to be a 

 linear function of the amount of chlorophyll present, 

 and a catalytic function of the pyocyanine added. The 

 actual numbers have gone as high as 700 muequivalents 

 of HVmg chlorophyll, or quite a bit in excess of what 

 one would expect for stoichiometry with X (maximal 

 yield 120 umoles/mg chlorophyll). As a matter of fact, 

 the H consumed is practically equal to the total 

 chlorophyll a present. This much of a proton shift is 

 probably consistent with the Mitchell hypothesis as to 

 the role of proton transport in the phosphorylation 

 mechanism. The trouble is, of course, that a pH shift 

 is highly non-specific. It could accompany either ion 

 transport into or out of an internal reservoir, or an 

 actual chemical change. Even if it represents ion 

 movement, the ion transport need not be the cause of the 

 energetic state of the chloroplasts. As in mitochondria 

 (18-21) it might easily be a reaction made possible by 

 the consumption of a small part of the energetic 

 intermediate. A pH shift also accompanies innumerable 

 chemical changes. It seems suggestive, for instance, 

 that transformation of bound histidine to its high 

 energy state as proposed recently by Boyer (.22) involves 

 production of hydroxyl ions. 



Our current uncertainties include the question of 

 the real function of X . We have no way of deciding 



