C-13-NMR ANALYSIS OF THE POSITIONAL DISTRIBUTION OF FATTY-ACIDS IN PLANT GLYCOLIPIDS

High-resolution, natural abundance C-13-NMR spectroscopy was used to a nalyze the positional distribution of fatty acids in the predominant p lant glycoglycerolipids. Fatty acid profiles attributed spectroscopica lly to the sn-l and sn-2 positions were in very good agreement with th e enzymatically measured distribution using a lipase from Rhizopus arr hizus. The C-13-NMR spectroscopy analysis makes use of small shift dif ferences of the acyl carbonyl carbons. As in other lipids, in glycolip ids sw-l-bound acyl carbonyls art: also shifted further downfield than the sn-2-bound carbonyls. Furthermore, in both positions the carbonyl shift depends on the distance to the nearest double bond resulting in identical series of incremental sequence shifts to higher fields from saturated to Delta 9, Delta 7 and Delta 6 double bonds, respectively. These deductions were enabled by analysis of galactolipids isolated f rom plants belonging to the Apiaceae and Boraginaceae, which contain h igh proportions of all-cis-Delta 7,10,13-hexadecatrienoic and all-cis Delta 6,9,12,15-octadecatetraenoic acid, respectively, in the sn-2 pos ition.