MELVIN CALVIN 



351 



The qiiiiione ilouble nci;aiive ion thus produced would then be a 

 sutficicutly j)o\\errul ictUuing agent in its Hj)id medium to reduce 

 such enzymatic colactors as Hj^oic acid or pyrithne nucleotide (18). 



The remaining positive ion in the dilorophyll matrix woidd have 

 to find its way to some donor, ultimately accepting electrons from 

 water. These donors might verv well be other metal ions such as 

 iron, which is very common in the chloroplast and which is as- 

 sociated with chlorophyll. In tact, a low temperature (70° K) light- 

 induced electron abstraction from a ferrocytochrome in a bacterium 

 has been reported (19). Room temperature photo-oxidation of the 

 ferrocytochromes of photosynthetic bacteria has been known for some 

 time (36, 37) . 



The system might structurally then bear some resemblance to the 

 model (see Fig. 19) Avhich we have used, the chlorophyll layer having 

 associated with it on one side the electron acceptor, quinone, in 

 a lipid environment, and on the other side electron donor materials, 

 such as the cytochromes, in an aqueous environment. Following 

 the absorption of a quantimi in chlorophyll (Fig. 29, equation 1) , 

 the energy will migrate by resonance transfer to a suitable site near the 

 quinone, at which point electron transfer to the quinone will take 



(I) hv~ 

 Cyt 



Fe- 



Cyt 



Fe"^^, 



(3) Cyt 



Chi 



r^ (2) 



© 



Cyt -CYTOCHROME AND/OR OTHER ELECTRON DONOR SYSTEMS 

 (AQUEOUS PHASE) 



- PLASTOQUINONE AND/OR OTHER ELECTRON ACCEPTOR 

 SYSTEMS (TPN, LIPOIC ACID, ETC.) LIPID PHASE 



Ctil- CHLOROPHYLL 



Chi + hv 



Chi 



Chl*+ Q 



Q + Chi 



3. Chi + Fe ► Fe + Chi 



lig. 29. Schematic arrangement of chlorophyll and possible donor and acceptor 

 molecules in the chloroplast. 



