605 



Jagendorf and Hind 



curves show directly and accurately, however, the rate 

 law for the dark decay reaction, and the steady state 

 level of X , The amount of X has interest in our 

 attempts to speculate on its nature. With pyocyanine, 

 at pH 6, equilibrium levels have been reported as high 

 as 60 mumoles per mg chlorophyll (2), On increasing the 

 phosphate level, to 10 mM, yields as high as II6 umoles 

 per mg chlorophyll have recently been obtained; and 

 extrapolation of a double reciprocal plot showed a 

 maximum yield of 120 umoles/mg chlorophyll at infinite 

 phosphate concentration. This is a ratio of 1 ATP 

 formed for every 9 chlorophyll molecules. Obviously X 

 cannot be a complex of an electron carrier such as 

 cytochrome f, with a coupling factor, as is the case for 

 one or more of the mitochondrial high energy intermediates 

 (10). X might involve plastoquinone A, however. 



Correlation with absorbancy and pH changes. 



With such a major entity any change in absorption 

 spectrum due to the transition to the energetic state 

 should be simple to observe spectrophotometrically. With 

 the kind cooperation of Drs. Britton Chance and Walter 

 Bonner we have attempted to look for such changes. Our 

 criteria for a preliminary correlation with the non- 

 phosphorylated intermediate included dependence on pH 6, 

 and more rapid kinetics and greater amounts with 

 pyocyanine than without. Essentially, we could find no 

 specific absorbancy change in the region between 480 and 

 590 mu which satisfied the above criteria. Also at 

 255 mu, in the region of the plastoquinone absorption, 

 we found only a minute spectral change, not dependent on 

 the more acid pH. Thus we are tempted to consider X 

 as being related only indirectly to the currently known 

 redox catalysts bound in the chloroplast membranes (with 

 the reservation, of course, that negative evidence is 

 never as conclusive as positive evidence). 



However we did observe very large changes in 

 absorbancy at almost all wavelengths examined, amounting 

 to as much as .05 OD unit, with 25 ugm of chlorophyll in 

 a 3 ml cuvette. These changes took as long as 15 or 30 

 seconds to saturate when pyocyanine was the cofactor, 

 and 2 to 3 minutes without a cofactor. Also, they were 

 pH 6 dependent. In a double beam spectrophotometer 

 deflections were seen even comparing one wavelength 



