The lipoxygenase LOXPsa1 of Pleurotus sapidus, originally investigated because of its ability to oxidize (+)-valencene to the valuable grapefruit aroma (+)-nootkatone, was isolated from the peptidase-rich lyophilisate using a three-step purification scheme including preparative isoelectric focusing and chromatographic techniques. Nano-liquid chromatography electrospray ionization tandem mass spectrometry (nLC-ESI-MS=MS) of the purified enzyme and peptide mass fingerprint analysis gave 38 peptides of the lipoxygenase from P. sapidus. Nearly 50% of the 643 amino acids long sequence encoded by the cDNA was covered. Both terminal peptides of the native LOXPsa1 were identified by de novo sequencing, and the postulated molecular mass of 72:5 kDa was confirmed. With linoleic acid as the substrate, the LOXPsa1 showed a specific activity of 113 U mg-1 and maximal activity at pH 7.0 and 30 °C, respectively.
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