THE LIPID BODY LIPOXYGENASE FROM CUCUMBER SEEDLINGS EXHIBITS UNUSUAL REACTION SPECIFICITY

The lipid body lipoxygenase of cucumber seedlings is at a high level e xpressed during the germinating process which is the stage of triglyce ride mobilisation. This enzyme exhibits an unusual positional specific ity which has not been described so far for any plant and animal lipox ygenase. The purified enzyme converts arachidonic acid to 15-S-hydrope roxy5Z,8Z,11Z, 13E-eicosatetraenoic acid (15S-HPETE), 12-S-hydroperoxy -5Z, 8Z, 10E, 14Z-eicosatetraenoic acid (12S-HPETE), and 8-S-hydropero xy-5Z,9E,11Z,14Z-eicosatetraenoic acid (8S-HPETE) in a ratio of 76:4:2 0 with the corresponding R-isomers being only minor contaminants. Bind ing to the lipid bodies enhances the arachidonic acid dioxygenase acti vity more than 4-times and alters positional specificity of the enzyme in favour of 8-S-hydroperoxy-5Z,9E,11Z,14Z-eicosatetraenoic acid (8S- HPETE) formation.