394 LIGHT AND LIFE 



tensities had concentrations exceeding those of other phosphorylated 

 metabolites by a factor of ten. More recent observations revealed 

 an inverse relationship between free diglycerophosphate and its esteri- 

 fied derivative, phosphatidyl glycerol. The concentration changes 

 shown in Fig. 3 occur within two or three minutes of illumination. 



The total concentration of glycerophosphate derivatives in Chlorella 

 approaches 10~- molar. This is largely within the chloroplast, and 

 the concentration there may be even higher. Metabolism on this 

 scale at this speed suggests that the nature of the lipid phase within 

 the lamellae may be changing upon illumination. Since glycerophos- 

 phate oxidation can provide one mole of DPNH and one of triose 

 phosphate, one may interpret the observed "reducing power" ac- 

 cumulation upon preillumination (10) and consequent enhanced 

 C^^Oo fixation in the dark. The reservoirs of glycerophosphate could 

 well provide this capacity, and further, the kinetics of the changes 

 described by Fig. 3 are of the same order as those observed for decay 

 of "reducing power" in Chlorella. Our observation that the con- 

 centration of DPN exceeds that of TPN in the chloroplasts may be 

 associated with this metabolic transformation. 



The Glycolipids 



The galactolipids comprise about two-thirds of chloroplast lipids. 

 They are even more rapidly labeled than phosphatidyl glycerol dur- 

 ing photosynthesis in C^^Oo (1, 2, 4) . The galactose moieties pos- 

 sessed most of the newly incorporated Ci'* while the activity in the 

 monoglyceride accumulated slowly. It is an obvious possibility, there- 

 fore, that the galactolipids are localized at the phase boundaries 

 adjacent to the transglycosylating enzymes of carbohydrate synthesis. 

 Their galactose is in surprisingly rapid equilil)rium with the nucleo- 

 tide diphosphogalactose pool observed by Buchanan et al. (3) . 



Plant Mitochondria 



The observed predominance of the galactolipids in photosynthetic 

 tissues and Wintermans' detailed study of chloroplast lipids (12) 

 suggested that these compounds are concentrated in the photosynthetic 

 structtire. The lipids of corn coleoptile mitochondria were examined 

 for comparison and found quite devoid of galactosyl monoglycerides. 

 The predominant smfactant lipid was phosphatidyl glycerol (ca. 

 80% in this group) . The mitochondria of animal tissues, on the other 

 hand, coiUain phosphatidyl esters of choline, ethanolamine, and 

 inositol with 10-15% of diphosphatidyl glycerol. 



