Multiple dioxygenation by lipoxygenase of lipids containing all-cis-1, 4, 7-octatriene moieties.

Soybean lipoxygenase-1 acting upon polyunsaturated fatty acids containing a suitably positioned all-cis-1,4,7-octatriene moiety generates bishydroperoxy derivatives while consuming approximately 2 mol of O₂ per mole of substrate. The reaction has been separated into two steps: The first is marked by the rapid monohydroperoxidation of the starting material and the second is marked by the much slower hydroperoxidation of the first product. All of the compounds which are successfully converted to bishydroperoxy derivatives contain an ω6,9,12 grouping of cis double bonds. α-Linolenic acid (ω3,6,9) cannot serve as a substrate because its preferred site of oxygenation is in the center of the octatriene moiety. The K_m for arachidonic acid in the reaction leading to the singly hydroperoxidized monohydroperoxide is 8.6× 10^?5, m, which is approximately 200 times smaller than the K_m for the monohydroperoxide in the second step leading to the bishydroperoxide. All of the substrates which undergo double dioxygenation form conjugated trienes.