LIPID FUNCTION IN THE PHOTOSYNTHETIC 



STRUCTURE 



A. A. Benson 



Department of Agricultural and Biological Chemistry 



The Pennsylvania State University 



University Park, Pennsylvania 



Lipids constitute about 30 per cent of the dry Aveight of the 

 chloroplast. Their high degree of orientation has been revealed by 

 determination (6) of birefringence by dye molecules absorbed in the 

 lipid regions. Chlorin orientation as a result of absorjDtion of the 

 phytol rest of the chlorophyll molecule in lipid media is generally 

 accepted. Most concepts of chloroplast structure and function em- 

 brace these considerations. 



The major fraction of the lipids within the chloroplast are sur- 

 factant molecules concentrated within the grana. Rather little neutral 

 triglycerides are observed. The two galactolipids (Fig. 1) predomi- 

 nate in the chloroplasts (2, 12) and in the chromatophores of photo- 

 synthetic bacteria. They differ from most lipids in that they have 

 but one fatty acid. The most important of the ionic surfactants are 

 the phosphatidyl glycerols (Fig. 2) and sulfodeoxyglycosyl mono- 

 glyceride (Fig. 1) , the plant suliolipid. It is proposed that these 

 neutral and anionic surfactants stabilize the large interfacial areas 

 between pigmented and protein phases of the lamellae. Their ad- 

 sorption at the interfaces would provide the physical medium neces- 

 sary to account for the observed structural and optical properties. 

 In addition, laminae of cationic or anionic functional groups would 

 allow a variety of suggestions for their function in the electron- 

 transfer reactions of photosynthesis. 



Light-Dependent Lh'Iu Metabolism 



The Phospholipids 



Phospliatidyl glycerol is the predominant j>hosphatidc in the photo- 

 synthetic structure and is by far the most actively metabolized (8) . 

 Observations l)y Miller in this laboratory revealed the active meta- 



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