Characterization of lipoxygenase oxidation products by high-performance liquid chromatography with electron impact-mass spectrometric detection

Lipoxygenase (LOX) is an enzyme that oxygenates polyunsaturated fatty acids to their corresponding hydroperoxy derivatives. For example, LOX found in plants produce the corresponding 13- and 9-hydroperoxide derivatives of lin oleic acid (13-HPOD and 9-HPOD). Identification of the HPOD products is usu ally accomplished by using gas chromatography with mass spectrometric (MS) detection, which requires extensive derivatization of the thermally unstabl e hydroperoxy group. Here we report a high-performance liquid chromatograph ic method in combination with electron impact (EI)-MS detection that separa tes and characterizes the HPOD isomers generated by soybean LOX type I oxyg enation of linoleic (LA) and linolenic acids as well as HPOD products produ ced by photosensitized oxidation of LA. The method does not required deriva tization of the hydroxyperoxide group, and location of its position can be determined by the EI-MS fragmentation pattern. The method has been used for the analysis of HPOD produced by action of partially purified LOX from the micro-alga Chlorella pyrenoidosa on LA. The study suggests the presence of two LOX isozymes in the micro-alga that oxygenate LA to its 13-HPOD and 9- HPOD derivatives. Moreover, the 9-LOX isozyme under anaerobic conditions cl eaves 13-HPOD to 13-oxo-tridecadienoic acid and pentane but does not cleave 9-HPOD.