6-Hydroxymellein synthetase as a multifunctional enzyme complex in elicitor-treated carrot root extract

Synthetic activity of a polyketide compound 6-hydroxymellein was induced in elicitor-treated carrot root tissues. The activity was significantly inhibited by an antiserum raised against the acyl carrier protein (ACP) of fatty acid synthetase, suggesting that the enzyme(s) for 6-hydroxymellein synthesis require(s) a functional unit similar to ACP. However, the synthetic activity was not stimulated by the addition of ACP purified from Escherichia coli and was not lost even after fractionation by gel-filtration chromatography. The active fraction obtained by gel-filtration (136 kDa) was subjected to immunoblot analysis, and a 128 kDa polypeptide in the fraction was found to cross-react with anti-ACP serum. These observations suggest that the biosynthesis of 6-hydroxymellein in carrot cells is catalyzed by an enzyme consisting of a single peptide chain.