Enantiospecifi c ( S ) - ( + ) - Linalool Formation from β - Myrcene by Linalool Dehydratase - Isomerase

In enzyme-catalyzed processes, the reaction pathway is defi ned by the enzyme and its complex with the substrate. The active site of an enzyme structure determines the interaction with the substrate which often results in high stereospecifi city. Classical examples are the reduction of nicotinamide-adenine-dinucleotides (NAD and NADP) and of aldehydes, the hydration of fumarate, and aldose-ketose isomerase reactions (Fersht, 1998). Fumarase reversibly catalyzes the formation of (S)-malate. The crystal structure reveals a tetrameric protein and the presence of two binding sites for dicarboxylic acids per monomer. One site also contains a water molecule (Weaver and Banaszak, 1996; Weaver, 2005). Enoyl-CoA-hydratases, which act stereospecifi c on α,β-unsaturated acyl-CoA thiolesters, contain also a water molecule in the active site (Wu et al., 2000; Bahnson et al., 2002). We discovered recently a novel enzyme in the anaerobic biodegradation pathway of monoterpenes, a linalool dehydratase-isomerase (LDI) (Brodkorb et al., 2010). In contrast to well-characterized enzymes acting on alkenes with adjacent polar groups, e.g. fumarate, the substrate β-myrcene has no polar group that may serve as anchor to bind the substrate and direct the reaction pathway. Hence, we explored whether the LDI catalyzes its reaction in a stereospecifi c manner.