On the mechanistic reasons for the dual positional specificity of the reticulocyte lipoxygenase

Abstract

A set of octadecadienoic acid isomers and selected eicosatrienoic acids were tested as substrates for the lipoxygenases from soybeans and reticulocytes. Among the dienoic fatty acids, 8Z, 11Z-octadecadienoic acid containing a n-9 doubly allylic methylene group turned out to be the substrate for the reticulocyte enzyme. This substrate was converted to its corresponding n-7 hydroperoxy derivative. The soybean lipoxygenase, in contrast, prefers the 9Z, 12Z-octadecadienoic acid (linoleic acid) which is oxygenated to its n-6 hydroperoxy derivative. In both cases a strong preference for the L S-isomer has been observed. Analysis of the oxygenation products formed from various eicosatrienoic acids indicated that 8Z, 11Z, 14Z-eicosatrienoic acid was converted by the reticulocyte enzyme to its 12S- and 15S-hydroperoxy derivative in a ratio of about 1:7 (dual positional specificity), whereas the 7Z, 10Z, 13Z-isomer was oxygenated predominantly (>97%) to its 14S-hydroperoxy derivative (singular positional specificity). 9Z, 12Z, 15Z-eicosatrienoic acid was oxygenated with a dual positional specificity to the corresponding 13- and 16-hydroperoxy compounds in a ratio of about 7:1. The soybean lipoxygenase converts the 8Z, 11Z, 14Z-isomer with a singular positional specificity to the corresponding 15S-hydroperoxy derivatives. The 9Z, 12Z, 15Z-eicosatrienoic acid, however, was oxygenated with a dual positional specificity to its 13S-hydroperoxy and 16S-hydroperoxy derivative in a ratio of about 1:4.