On the Specificity of the Oxygenation of Unsaturated Fatty Acids Catalyzed by Soybean Lipoxidase

TLDR

Abstract

Abstract The positional and stereochemical specificities of the soybean lipoxidase-catalyzed oxygenation of unsaturated fatty acids have been investigated. It was found that the oxygen function was introduced at position ω6 in all of the fatty acids which reacted. In one case a small amount of the substrate was oxygenated in position ω10. The structural requirement for substrates is the presence of a cis, cis-1,4-pentadiene group with its methylene group located in position ω8. The structure of the hydroperoxy acid formed from 8,11,14-eicosatrienoic acid was 15l-hydroperoxy-8(cis), 11(cis),13(trans)-eicosatrienoic acid. By using sterospecifically tritium-labeled 8,11,14-eicosatrienoic acids, it was found that the removal of hydrogen from the ω8 methylene group is stereospecific. Thus, only the hydrogen of the l configuration is removed by the enzyme during the conversion into 15l-hydroperoxy-8(cis), 11(cis),13(trans)-eicosatrienoic acid. The conversion of [13l-3H, 3-14C]8,11,14-eicosatrienoic acid is accompanied by an isotope effect, suggesting that the hydrogen removal occurs as the initial step of the reaction.