Manganese lipoxygenase oxidizes bis-allylic hydroperoxides and octadecenoic acids by different mechanisms

► Mn-lipoxygenase rapidly oxidizes bis-allylic hydroperoxides (LOOH) to radicals (LOO⋅). ► Monounsaturated fatty acids are oxidized only slowly by Mn-lipoxygenase. ► The dissociation enthalpies of LOO-H and allylic C-H bonds are almost identical. ► Both oxidations occur by proton-coupled electron transfer to the lipoxygenase. ► Proton transfer from LOOH to the catalytic base Mn3+OH− is facilitated by dissociation.