LOX_Psa1, the first recombinant lipoxygenase from a basidiomycete fungus

A dioxygenase from the edible basidiomycete Pleurotus sapidus, originally researched because of its distinct ability to convert the sequiterpene (+)-valencene to the valuable grapefruit aroma (+)-nootkatone, was identified as a potent lipoxygenase (LOX_Psa1). Kinetic parameters, pH and temperature optima of the pure recombinant enzyme were determined using linoleic acid as the substrate. K_m, v_max, and k_cat were 40.3 μM, 130.3 U mg^-1, and 157 s^-1, respectively. The maximal enzymatic activity was found at pH 7.0 and 35°C. Showing high specificity toward free linoleic acid, the enzyme was classified as lipoxygenase type 1. Conversion of linoleic acid yielded mainly (S)-13-hydroperoxy-9Z,11E- octadecadienoic acid (94% ee), as was confirmed by chiral HPLC analysis of the hydroperoxides. The amino acid sequence showed homology to lipoxygenases catalyzing S stereospecific oxygenation, and thus the enzyme was characterized as a 13S-lipoxygenase. This is the first lipoxygenase described to accept terpene hydrocarbons as substrates.