| Abstract: | A lipoxygenase obtained from the fungus Fusarium oxysporum was purified and crystallized. Using the purified enzyme, the positional specificity of linoleate peroxidation was studied. Linoleate hydroperoxides were converted into the corresponding trimethylsilyl derivative by reduction, catalytic hydrogenation and treatment with hexamethyldisilazane/trimethylchlorosilane/pyridine and then analyzed by combined gas-liquid chromatography-mass spectrometry. Fusarium lipoxygenase was found to produce 9- or 13-hydroperoxy-octadecadienoates from linoleate. The ratio of 9- to 13-hydroperoxides produced by the enzyme was also determined by high performance liquid chromatography of their methyl esters. When the enzymic reaction proceeded at pH 9.0 and 12.0, the ratio of 9- to 13-hydroperoxide isomers was 70 : 30 and 56 : 44, respectively. With the use of the heavy isotope of oxygen (18O2), atoms of oxygen introduced into hydroperoxides were found to be derived from the gaseous phase and not from the aqueous phase. |
