Characterization of the linoleic acid Δ9 hydratase catalyzing the first step of polyunsaturated fatty acid saturation metabolism in Lactobacillus plantarum AKU 1009a

Linoleic acid Δ9 hydratase, which is involved in linoleic acid saturation metabolism of Lactobacillus plantarum AKU 1009a, was cloned, expressed as a his-tagged recombinant enzyme, purified with an affinity column, and characterized. The enzyme required FAD as a cofactor and its activity was enhanced by NADH. The maximal activities for the hydration of linoleic acid and for the dehydration of 10-hydroxy-cis-12-octadecenoic acid (HYA) were observed at 37 °C in buffer at pH 5.5 containing 0.5 M NaCl. Free C16 and C18 fatty acids with cis-9 double bonds and 10-hydroxy fatty acids served as substrates for the hydration and dehydration reactions, respectively. The apparent Km value for linoleic acid was estimated to be 92 μM, with a kcat of 2.6∙10−2 s−1 and a Hill factor of 3.3. The apparent Km value for HYA was estimated to be 98 μM, with a kcat of 1.2∙10−3 s−1.