From Hypothesis to Experimental Evidence: Reversibility of Fatty Acid Hydratases Exemplified for Dehydration of ( S , Z )‐13‐Hydroxyoctadec‐9‐enoic Acid

ABSTRACT

While hydration of linoleic acid under formation of ( S , Z )‐13‐hydroxyoctadec‐9‐enoic acid is the natural reaction of linoleic acid hydratase from Lactobacillus acidophilus , in this work we demonstrate that this enzyme is also capable of catalyzing the reverse reaction that is dehydration. Proceeding under thermodynamic control, at 20 mM substrate concentration this biotransformation resulted in an equilibrium with a ratio of ( S , Z )‐13‐hydroxyoctadec‐9‐enoic acid to linoleic acid of ca. 80:20. Thus, our work represents further evidence that fatty acid hydratases are also capable of catalyzing dehydration of secondary fatty acid‐derived alcohols. Besides being of fundamental significance for understanding this enzyme class and rationalizing the incomplete conversion in biocatalytic hydration of unsaturated fatty acids, these results also open up a perspective for a novel chemistry that is the conversion of a broad range of (aliphatic) secondary alcohols to alkenes in water at room temperature in the presence of a fatty acid dehydratase.

Practical Applications : Although this study centers on the fundamental understanding of catalytic properties of fatty acid hydratases, exemplified for a linoleic hydratase from Lactobacillus acidophilus , two potential industrial applications of such biocatalysts are addressed as well. First, the understanding of this type of hydration step as a kinetically versus thermodynamically controlled reaction will support process development work on this biotransformation. This type of biotransformation is of high interest for the chemical industry because the resulting hydroxy fatty acids represent bio‐based monomers being suitable to build polymers, for example, polyesters, and their access is based on unsaturated fatty acids as readily available and cheap biorenewable feedstocks. Second, as a long‐term perspective, the suitability of this enzyme class for the reverse reaction, which is the dehydration step and which was demonstrated in this work, could enable the access to alkenes in an environmentally friendly fashion when starting from aliphatic alcohols that are now already available from renewable feedstocks.