Interactions of sulfhydryl agents and soybean lipoxygenase inhibitors

The enzymic conversion of 5,8,11,14-eicosatetraenoic acid to the corresponding hydroperoxy fatty acids by soybean lipoxygenase (lineolate: oxygen oxidoreductase E.C. 1.13.11.12.) was investigated and a simple selective extraction method was introduced. The known inhibition of the lipoxygenase pathway by phenidone, mercuric chloride, methylmercuric chloride, methylmercuric iodide, 1,5-dihydroxynaphthalene and acetone phenylhydrazone was influenced by thiol compounds in different ways. (1) A total reactivation of lipoxygenase activity was achieved when several thiol compounds, especially gluthatione, were preincubated with the inhibitor mercuric chloride and the enzyme. (2) A remarkable reduction of the inhibitory potency of phenidone against soybean lipoxygenase was seen when thiol compounds were preincubated with the enzyme before the addition of the inhibitor. When phenidone was preincubated with lipoxygenase first, sulfhydryl agents did not restore the enzyme activity. (3) No interaction was seen, when glutathione or other thiol compounds and the lipoxygenase inhibitors 1,5-dihydroxynaphthalene, nordihydroguaiaretic acid and acetone phenylhydrazone were tested against the enzyme. Therefore, we suggest that soybean lipoxygenase inhibitors may act via different modes of action. It is important to study the mechanisms of lipoxygenase inhibitors, since mammalian lipoxygenase and their products are known to be involved in the inflammatory response.