80 SAPONIFIABLE LIPIDS 



In addition to the general references, reviews of the phosphatides may be found in 

 the papers of Sperry (14) and of Horhammer and Wagner (15). 



GLYCOLIPIDS 



As has been noted in the previous section, some of the complex phospholipids con- 

 tain sugar moieties. However, the term "glycolipid" is normally reserved for lipids con- 

 taining sugar units but not phosphorus. Only recently has it become evident that such 

 compounds are widely distributed in plants, especially in green leaves (7, 16). For ex- 

 ample, in alfalfa galactosyl compounds are the major component of the lipid fraction. 

 The general structure of a monogalactosyl glyceride is shown below. Higher homologues 

 have as many as 5 galactose residues linked (l-'C) to each other. 



(|H2 



HCOH 



I 

 HjCOCCjjHjg 







monogalactosyl glyceride 



A sulfonic acid related to 6-deoxyglucose is present as the major anionic lipid in 

 chloroplasts of many plants (17). A suggested structure is as follows: 



CH 



2 



I 

 HCOH 



H2C0C(CH2)7CH=CH(CH2)7CH3 

 



Such a compound could well act as a surface -active agent in holding together the polar and 

 non-polar regions of the chloroplast. 



Plant glycolipids differ from the animal cerebrosides in that the latter have sphingo- 

 sine rather than glycerol. However, both the cerebrosides and plant glycolipids may be 

 described as saponifiable lipids containing one or more sugar units but no phosphorus. 

 True cerebrosides have been reported to occur in plants (18), but they have not been 

 studied extensively. 



ISOLATION 



Isolation of the different categories of lipids has relied heavily on differences in 

 their solubilities. As with many other plant products the first precaution to be observed 



