title: Sequential oxygenation of linoleic acid in the fungus Gaeumannomyces graminis: stereochemistry of dioxygenase and hydroperoxide isomerase reactions.
abstract: Linoleic acid is sequentially oxygenated to (7S,8S)-dihydroxylinoleic acid by dioxygenase and hydroperoxide isomerase activities present in the fungus Gaeumannomyces graminis (Brodowsky, I. D., Hamberg, M., and Oliw, E. H., J. Biol. Chem. 267, 14738-14745 (1992)). Linoleic acids stereospecifically deuterated at C-7 and C-8 were prepared by biological desaturation of the corresponding stearates and used to determine the stereochemistry of the hydrogen abstractions occurring in the dioxygenase- and hydroperoxide isomerase-catalyzed reactions. The dioxygenase reaction was found to involve stereospecific abstraction of the pro-S hydrogen from C-8 followed by antarafacial insertion of dioxygen to produce (8R)-hydroperoxylinoleic acid. The hydroperoxide isomerase reaction consisted of conversion of (8R)-hydroperoxylinoleic acid into (7S,8S)-dihydroxylinoleic acid by stereospecific elimination of the pro-S hydrogen from C-7 and intramolecular suprafacial insertion of oxygen at C-7. Accordingly, during the conversion of linoleic acid into (8R)-hydroperoxylinoleic acid, the absolute configuration of C-8 was inverted, while the conversion of (8R)-hydroperoxylinoleic acid into (7S,8S)-dihydroxylinoleic acid occurred with retention of absolute configuration at C-7.
authors.affiliation: Department of Physiological Chemistry, Karolinska Institutet, Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Hamberg
authors.forename: L Y
authors.initials: LY
authors.lastname: Zhang
authors.forename: I D
authors.initials: ID
authors.lastname: Brodowsky
authors.forename: E H
authors.initials: EH
authors.lastname: Oliw
mesh_terms: D003903:Deuterium; D019746:Intramolecular Oxidoreductases; D007535:Isomerases / Q000378:metabolism*; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000737:chemistry / Q000378:metabolism*; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D013098:Xylariales / Q000201:enzymology*
chemical_list: D008041:Linoleic Acids; D019787:Linoleic Acid; D003903:Deuterium; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; C021377:hydroperoxide isomerase