On the mechanistic reasons for the dual positional specificity of the reticulocyte lipoxygenase.
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 best 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 LS-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 (greater than 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.
Kühn
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H
Institute of Biochemistry, School of Medicine (Charité), Humboldt University, Berlin, F.R.G.
Heydeck
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D
Sprecher
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H
D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D008084:Lipoxygenase / Q000378:metabolism*; D013058:Mass Spectrometry; D010100:Oxygen / Q000378:metabolism*; D012156:Reticulocytes / Q000201:enzymology*; D013025:Glycine max / Q000201:enzymology
D008084:Lipoxygenase; D010100:Oxygen