Acyl Coenzyme A Preference of Diacylglycerol Acyltransferase from the Maturing Seeds of Cuphea, Maize, Rapeseed, and Canola

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Abstract
In their seed triacylglycerols, Cuphea carthagenesis contain 62% lauric acid; maize [Zea mays] possess 50% linoleic acid and 30% oleic acid; rapeseed (Brassica napus L. var Dwarf Essex) has 40% erucic acid; and canola (Brassica napus L. var Tower) holds 60% oleic acid and 23% linoleic acid. Diacylglycerol acyltransferase (EC 2.3.1.20) in the microsomal preparations from maturing seeds of the above species were tested for their preference in using different forms of acyl coenzyme A (CoA). Lauroyl CoA, oleoyl CoA and erucoyl CoA individually or in equimolar mixtures at increasing concentrations were added to the assay mixture containing diolein, and the formation of triacylglycerols from the acyl groups at 24, 32, and 40.degree. C was analyzed. The Cuphea enzyme preferred lauroyl CoA to oleoyl CoA, and was inactive on erucoyl CoA. The maize enzyme had about equal activities on oleoyl CoA and lauroyl CoA, and was inactive on erucoyl CoA. Enzymes from both rapeseed and Canola had the same pattern of acyl CoA preference, with highest activities on lauroyl CoA. The two enzymes were more active on oleoyl CoA than on erucoyl CoA at high acyl CoA concentrations (10 and 20 micromolar) at 24.degree. C, but were more active on erucoyl CoA than on oleoyl CoA at low acyl CoA concentrations (1.36 micromolar or less) at 32 and 40.degree. C. These findings are discussed in terms of the contribution of the enzyme to the acyl specificity in storage triacylglycerols and the implication in seed oil biotechnology.