Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/2006
Publication Date: 12/6/2006
Citation: Lin, J.T., Arcinas, A.J. 2006. Regiospecific analysis of diricinoleoyl-acyl-glycerol in castor oil using electrospray ionization-mass spectrometry. Meeting Abstract. Interpretive Summary: Ricinoleate, an industrially useful hydroxy fatty acid occurs abundantly as triacylglycerols (TAG) in castor bean, in addition to the toxin, ricin. The stereospecific determination of diricinoleoyl-acyl-glycerol containing one non-hydroxyl-fatty acid chain in castor oil helps explain a key enzymatic step involved on the biosynthetic pathway of castor oil. The pathway can be used for the development of transgenic oilseeds to produce a castor oil substitute lacking this toxic component. We have used mass spectrometry to show the locations of these three fatty acid chains on the glycerol backbone of molecules of triacylglycerols.
Technical Abstract: HPLC fractions of castor oil were used to identify the regiospecific location of non-hydroxyl fatty acids on glycerol backbone in diricinoleoyl-acyl-glycerols using electrospray ionization MS3 of lithium adducts. The regiospecific ions in MS3 spectra were from the loss of 'a,B'-unsaturated fatty acid specific to sn-2 position. The content of 1,3-diricinoleoyl-2-oleoyl-sn-glycerols (ROR) in three stereospecific isomers of diricinoleoyl-acyl-glycerols (RRO, ROR and ORR) combined in castor oil is about 88%. The contents of other diricinoleoyl-acyl-glycerols containing a non-hydroxyl fatty acids in the three stereospecific isomers combined are as follows: 1,3-diricinoleoyl-2-linoleoyl-sn-glycerol (RLR, 95%), 1,3-diricinoleoyl-2-linolenoyl-sn-glycerol (RLnR, 96%), 1,3-diricinoleoyl-2-stereoyl-sn-glycerol (RSR, 100%), 1,3-diricinoleoyl-2-palmitoyl-sn-glycerol (RPR, 78%) and 1,3-diricinoleoyl-2-lesqueroleoyl-2-sn-glycerol (RLsR, 31%). On the key enzymatic step of the biosynthetic pathway of castor oil, the conversion of 2-oleoyl-phosphatidylcholine (2-oleoyl-PC) to 2-ricinoleoyl-PC by 12-oleoyl-hydroxylase, castor phospholipase A2 is specific to PC containing a hydroxyl fatty acid at the sn-2 position in vivo. The phospholipase A2 hydrolysis of PC containing a non-hydroxyl fatty acid at sn-2 position is either blocked or partially blocked in vivo and these non-hydroxyl fatty acids stay mostly at sn-2 position of triacylglycerol in castor oil. The Lesqueroleoyl chain on diricinoleoyl-lesqueroleoyl-glycerol seems equally distributed on the three sn-positions. 2-Lesqueroleoyl-PC can be hydrolyzed by castor phospholipase A2 as well as 2-ricinoleoyl-PC.