Research Group Biochemical Ecology and Molecular Evolution

Project: Annika Engelhardt

Biochemical Characterization of the Acetohydroxyacid Synthase of Lycopsamine Type Pyrrolizidine Alkaloids

The biosynthesis of pyrrolizidine alkaloids (PAs) can be divided in two general parts, the formation of the necine base and of the necic acid. While the synthesis for the necine base is believed to be the same for all PAs, the synthesis of the necic acid results in various molecules that are esterified to the necine base. For lycopsamine type PAs it is postulated that the first step of the formation of the necic acid is catalyzed by an acetohydroxyacid synthase (AHAS).

The aim of this study is to confirm that an AHAS is involved in lycopsamine type PA biosynthesis and to elucidate the order of biosynthesis steps to the esterified necic acid (see fig. 1). Therefore, two possible candidate enzymes of Heliotropium indicum are characterized with respect to substrate specificity. In addition, an analytical approach with HPLC, GC-MS, and FTICR is used to identify intermediates of the pathway in root cultures of Symphytum officinale.

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Figure 1: The three possible scenarios of PA biosynthesis proposing that the three essential steps "pro necic acid biosynthesis", “esterification” and “reduction” are interchanged (Langel, 2008). Click figure for higher resolution.