ARS | Publication request: The Enzymology of Castor Oil Biosynthesis

Submitted to: Association for the Advancement of Industrial Crops Conference
Publication Type: Abstract
Publication Acceptance Date: August 1, 2006
Publication Date: October 15, 2006
Citation: McKeon, T.A., He, X., Chen, G.Q., Lin, J.T. 2006. The Enzymology of Castor Oil Biosynthesis. Association for the Advancement of Industrial Crops Conference.

Technical Abstract: Castor oil is an important industrial oil used to produce greases, lubricants, coatings, detergents, monomers for plastic production, plasticizers, and cosmetics. The oil is unusual in that the fatty acid component is 90% ricinoleic acid. There has been considerable interest in developing an alternate source of high ricinoleate oil. We have shown that ricinoleate is incorporated 6-fold greater extent than oleate in the final step of oil biosynthesis, the acylation of diacylglycerol to triacylglycerol. There are several enzymes that can carry out this final acylation step. These are the acylCoA-dependent diacylglycerol acyltransferases (DGAT), types 1 and 2, and the phospholipid-diacylglycerol acyltransferase (PDAT). We have cloned genes for the two DGATs from developing castor seed and expressed them in yeast. The DGAT type 1 shows a preference for acylating diacylglycerols containing ricinoleate. The DGAT type 2 shows very poor activity in the yeast expression system. We have also cloned two genes encoding acylCoA synthetases (ACS). One of these genes encodes an enzyme that shows preference for using oleate and other "hydrocarbon" fatty acids, while the other ACS shows a threefold preference for using ricinoleate. Taken together, the substrate preference of the DGAT type 1 and the ACS account for the sixfold preference we have observed for isolated castor microsomes incorporating ricinoleate into the triacylglycerol fraction.