title: The novel pathway for ketodiene oxylipin biosynthesis in Jerusalem artichoke (Helianthus tuberosus) tubers.
abstract: The new route of the plant lipoxygenase pathway, directed specifically towards the ketodiene formation, was detected during in vitro experiments with Jerusalem artichoke (Helianthus tuberosus) tubers. Through this pathway (9Z,11E,13S)-13-hydroperoxy-9,11-octadecadienoic acid (13-HPOD) is reduced to corresponding 13-hydroxy acid (13-HOD), which is in turn dehydrogenated into ketodiene (9Z,11E,13S)-13-oxo-9,11-octadecadienoic acid (13-KOD). Dehydrogenation of 13-HOD into 13-KOD was not dependent on the presence of either NAD or NADP, but was strongly dependent on the presence of oxygen. Under anoxic conditions, 13-HOD dehydrogenation was blocked, but addition of 2,6-dichlorophenolindophenol restored it. Sulfite addition fully suppressed the aerobic dehydrogenation of 13-HOD. Hydrogen peroxide is a by-product formed by the enzyme along with 13-KOD. These data suggest that the ketodiene biosynthesis in H. tuberosus tubers is catalyzed by flavin dehydrogenase. (9S,10E,12Z)-9-Hydroxy-10,12-octadecadienoic acid (9-HOD) is dehydrogenated by this enzyme as effectively as 13-HOD, while alpha-ketol, (9Z)-12-oxo-13-hydroxy-9-octadecenoic acid, and ricinoleic acid did not act as substrates for dehydrogenase. The enzyme was soluble and possessed a pH optimum at pH 7.0-9.0. The only 13-HOD dehydrogenase known so far was detected in rat colon. However, unlike the H. tuberosus enzyme, the rat dehydrogenase is NAD-dependent.
authors.affiliation: Laboratory of Oxylipins, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, Lobatchevsky str., 2/31, P.O. Box 30, Kazan 420111, Russia. chechyotkin@mail.knc.ru
authors.forename: Ivan R
authors.initials: IR
authors.lastname: Chechetkin
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Medvedeva
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Grechkin
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D006368:Helianthus / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000378:metabolism; D042541:Intracellular Space / Q000378:metabolism; D008041:Linoleic Acids / Q000378:metabolism; D008042:Linolenic Acids / Q000096:biosynthesis* / Q000737:chemistry; D008054:Lipid Peroxides / Q000378:metabolism; D008084:Lipoxygenase / Q000378:metabolism; D015394:Molecular Structure; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D010088:Oxidoreductases / Q000378:metabolism; D010104:Oxygen Radioisotopes; D035281:Plant Tubers / Q000378:metabolism*; D051381:Rats; D021241:Spectrometry, Mass, Electrospray Ionization; D013379:Substrate Specificity
chemical_list: D002250:Carbon Radioisotopes; D008041:Linoleic Acids; D008042:Linolenic Acids; D008054:Lipid Peroxides; D010104:Oxygen Radioisotopes; D009243:NAD; C038649:13-hydroperoxy-9,11-octadecadienoic acid; C064441:13-oxo-9,11-octadecadienoic acid; C024348:13-hydroxy-9,11-octadecadienoic acid; D009249:NADP; D010088:Oxidoreductases; D008084:Lipoxygenase