The inactivation of lipoxygenases by acetylenic fatty acids

5,8,11,14-eicosatetraynoic acid (ETYA) inactivates irreversibly the lipoxygenases from soybeans and reticulocytes in a time-dependent manner. 5,8,11-eicosatriynoic acid (ETrYA) is a powerful inactivator only for reticulocyte lipoxygenase. Several types of experimental evidence indicate that the acetylenic fatty acids act as suicidal substrates which are converted during the lipoxygenase reaction probably to allene hydroperoxides. These highly reactive intermediates or radical precursors react immediately with a methionine residue at the active centre of the enzyme forming one methionine sulfoxide per molecule. Experiments with 14C-labelled ETYA-methylester show that despite complete enzyme inactivation no covalent binding of the suicidal substrate to the lipoxygenases occurred.