BENTLEY GLASS 875 



ol lipids. A. A. licnson has suininari/.ecl sonic aspects ol the pKjblcm. 

 The lipids are in the grana and are highly oriented. Two galacto- 

 lipids predominate. There is also phosphatidyl glycerol, the pre- 

 dominant phosphatide. Diglycerophosphate and phosphatidyl glyc- 

 erol iMidergo reciprocal changes in amount during illumination of 

 cells (Chlorella) . In the dark, the lipid diminishes in amount, but 

 is rapidly replenished at the expense ot the diglycerophosj^hate when 

 illumination returns. The reservoirs of glycerophosphate may pro- 

 vide "reducing power" w'hich can be accunnilated during illumina- 

 tion and afterwards serve to fix CO2 in the dark. The galactolipids 

 are galactosyl diglycerides, and include monogalactosyl, digalactosyl, 

 and sulfodeoxygalactosyl types. They very rapidly incorporate labeled 

 C^'* from C^^Oo during photosynthesis and are presimiably located 

 at the phase boimdaries adjacent to the transglycosylating enzymes 

 of carbohydrate synthesis. In the chloroplast lamellae, the galactose 

 moieties are presimiably in contact with the stroma and the fatty 

 acids in a lipid layer adjacent to a protein-rich phase. There might 

 be two types of lipid laminae, an outer one "dominated by galacto- 

 lipids in the region of carbohydrate synthesis and an inner one domi- 

 nated by chlorophyll and electron transport systems in the region of 

 oxygen production." 



James Franck, who bases his views on the properties of chlorophyll 

 a, W'hich undergoes both n — ^ tt* and tt ^> n* transitions, conceives of 

 a sandwich-like structure, w^ith chlorophyll lying between layers of 

 lipid and protein and protected from fluid water, except for a small 

 percentage of exposed molecules. Strongly protected chlorophyll 

 molecules, when excited, pass excitation energy to the exposed chloro- 

 phyll molecules by resonance transfer. This results in a metastable 

 triplet state. The accessory pigments transfer singlet excitation. Pre- 

 umably the metastable triplet state can carry out only one of the two 

 photochemical steps in the splitting of water; singlet excitation is 

 needed for the other. 



The Relation of Photophosphorylation to Photosynthesis 



In 1954 it was established by Daniel Arnon and his collaborators 

 that isolated chloroplast systems can in fact fix carbon dioxide, and 

 that photosynthesis can in fact be conducted outside the living cell. 

 Now, six years later, a vast amount of additional work on the prob- 

 lem, done in many laboratories, is ripe for fresh interpretation and 

 a new synthesis of ideas. Arnon has in several recent papers at- 

 tempted this labor; and in the present Symposium he has in fact 



