Abstract
The fungus Gaeumannomyces graminis metabolized linoleic acid extensively to (8R)-hydroperoxylinoleic acid, (8R)-hydroxylinoleic acid, and threo-(7S,8S)-dihydroxylinoleic acid. When G. graminis was incubated with linoleic acid under an atmosphere of oxygen-18, the isotope was incorporated into (8R)-hydroxylinoleic acid and 7,8-dihydroxylinoleic acid. The two hydroxyls of the latter contained either two oxygen-18 or two oxygen-16 atoms, whereas a molecular species that contained both oxygen isotopes was formed in negligible amounts. Glutathione peroxidase inhibited the biosynthesis of 7,8-dihydroxylinoleic acid. These findings demonstrated that the diol was formed from (8R)-hydroperoxylinoleic acid by intramolecular hydroxylation at carbon 7, catalyzed by a hydroperoxide isomerase. The (8R)-dioxygenase appeared to metabolize substrates with a saturated carboxylic side chain and a 9Z-double bond. G. graminis also formed omega 2- and omega 3-hydroxy metabolites of the fatty acids. In addition, linoleic acid was converted to small amounts of nearly (65% R) racemic 10-hydroxy-8,12-octadecadienoic acid by incorporation of atmospheric oxygen. An unstable metabolite, 11-hydroxylinoleic acid, could also be isolated as well as (13R,13S)-hydroxy-(9E,9Z), (11E)-octadecadienoic acids and (9R,9S)-hydroxy-(10E), (12E,12Z)-octadecadienoic acids. In summary, G. graminis contains a prominent linoleic acid (8R)-dioxygenase, which differs from the lipoxygenase family of dioxygenases by catalyzing the formation of a hydroperoxide without affecting the double bonds of the substrate.
Highlights
From the Department of Pharmaceutical Pharmacology, Uppsala University Biomedical Center, Uppsala, Sweden and the §Department of Physiological Chemistry, Karolinska Institutet, Stockholm, Sweden
The 100,000 x g supernatant of G. graminis was recently found to metabolize linoleic acid to (8R)-HODE,l 16-HODE, 17-HODE, and polar metabolites, which were not characterized (7).The hydroxylation of fatty acids at the wl,w2, or o3-position is catalyzed by cytochrome P-450 in mammals, microorganisms, and fungi
Little is known about the biosynthesis of (8R)-HODE and itsbiological significance.CYLinolenic acid was metabolized to its 8-hydroxy metabolite, but arachidonic acid and eicosapentaenoic acid were not oxide isomerase
Summary
The Me3Si ether methyl ester derivative of the hydrogenated compound (Fig. 4B) showed ions at m/z 474 (M+),[459]. 18:3n-3-Incubations of 18:3n-6 resulted in formationof at due to a technical mistake in the preparation of the culture least five products They were separated by TLC, and the broth (discolored due toa Maillard reaction).G. graminis was three major metabolites were identified by their mass spectra grown on amoredefinedmedium that was based on as 7,8-DiHOTrE (RF value of 0.12, and C-value of 20.7), 8- casamino acids instead of yeast extract.
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