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Thomas A. McKeon,
tmckeon@pw.usda.gov, Xiaohua He, xiaohua@pw.usda.gov, Grace Q. Chen,
qhgc@pw.usda.gov, and Jiann-Tsyh Lin, jtlin@pw.usda.gov. Western
Regional Research Center, USDA-Agricultural Research Service, 800
Buchanan St, Albany, CA 94710
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| Castor oil is unique among commodity oils in its
fatty acid composition and consists of 90% ricinoleate
(12-hydroxy-octadec-cis-9-enoate). The mid-chain hydroxyl group
imparts physical and chemical properties that make it useful in many
industrial applications. Among its uses are lithium grease, surfactants,
cosmetics, polymers, and engineering plastics. Biochemically, the castor
seed is very efficient in converting oleate to ricinoleate (>90%
efficiency). This efficiency results from the high rate of ricinoleate
incorporation into the triacylglycerol fraction, with concomitant
exclusion of oleate. We have identified two enzymes which carry out the
final step of castor oil biosynthesis, cloned cDNAs for these, and
demonstrated that the substrate preferences of these two enzymes
explains the efficient incorporation of ricinoleate into
triacylglycerol. We believe that inclusion of these enzymes in a
transgenic or microbial system could enhance the production of a castor
oil substitute. |