Anaerobic lipoxygenase activity from Chlorella pyrenoidosaresponsible for the cleavage of the 13‐hydroperoxides of linoleic and linolenic acids

An enzyme from the alga Chlorella pyrenoidosa, previously identified as a hydroperoxide lyase (HPLS), cleaves the 13‐hydroperoxide derivatives of linoleic and linolenic acids into a volatile C5 fragment and a C13 oxo‐product, 13‐oxo‐9(Z),11(E)tridecadienoic acid (13‐OTA). Gas chromatography/mass spectrometry (GC/MS) headspace analysis of the volatile products indicated the formation of pentane when the substrate was the 13‐hydroperoxide derivative of linoleic acid, whereas a more complex mixture of hydrocarbons was formed when the 13‐hydroperoxide derivative of linolenic acid was the substrate. Analysis of the nonvolatile products by GC/MS and liquid chromatography/mass spectrometry (LC/MS) indicated the formation of 13‐OTA along with the 13‐ketone derivative. This enzymatic activity was inhibited by oxygen but was restored with nitrogen. The enzymatic cleavage activity was coincidental in purified fractions with lipoxygenase activity that produced the 13‐ and 9‐hydroperoxide derivatives of linolenic acid. The results suggest that the enzymatic cleavage activity in Chlorella pyrenoidosawas not a consequence of hydroperoxide lyase activity as previously thought, but was due to anaerobic lipoxygenase activity. This enzyme fraction was purified by (NH4)2SO4precipitation, gel filtration, and hydrophobic interaction chromatography. The purified enzyme has an approximate MW of 120 KDa and maximum activity at pH 8.0.