title: Hydroperoxide lyases (CYP74C and CYP74B) catalyze the homolytic isomerization of fatty acid hydroperoxides into hemiacetals.
abstract: The conversion of linoleic acid 9-hydroperoxide (9-HPOD) by recombinant melon (Cucumis melo L.) hydroperoxide lyase (HPL, CYP74C subfamily) was studied. Short (5 s-1 min) incubations at 0 degrees C followed by rapid extraction and trimethylsilylation made it possible to trap a new unstable (t(1/2) <30 s) product, i.e. the hemiacetal (1'E,3'Z)-9-hydroxy-9-(1',3'-nonadienyloxy)-nonanoic acid. Identification was performed by GC-MS analysis and substantiated by the formation of trimethylsilyl 9-trimethylsilyloxy-9-nonyloxy-nonanoate upon catalytic hydrogenation and by (2)H-labelling experiments. Both (18)O atoms of [(18)O(2)-hydroperoxy]9-HPOD were incorporated into the hemiacetal. Along with the hemiacetal, three chain-cleavage products, i.e. the enol (1E,3Z)-nonadienol and the hydrates of 3(Z)-nonenal and 9-oxononanoic acid, were trapped as their trimethylsilyl derivatives. The kinetics of (18)O incorporation from [(18)O(2)]9-HPOD provided strong evidence that the cleavage products originated in the hemiacetal. Linolenic and linoleic acid 13-hydroperoxides served as substrates for recombinant HPLs of melon, alfalfa (Medicago sativa) and guava (Psidium guajava), and in each case hemiacetals and enols were detectable by the trapping technique. The data obtained demonstrated that CYP74C and CYP74B HPLs act as isomerases performing a homolytic rearrangement of fatty acid hydroperoxides into short-lived hemiacetals which upon decomposition produce 3(Z)-nonenal, 3(Z)-hexenal and other short chain aldehydes.
authors.affiliation: Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, Kazan, 420111 Russia. grechkin@mail.knc.ru
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Grechkin
authors.forename: Fredi
authors.initials: F
authors.lastname: Brühlmann
authors.forename: Lucia S
authors.initials: LS
authors.lastname: Mukhtarova
authors.forename: Yuri V
authors.initials: YV
authors.lastname: Gogolev
authors.forename: Mats
authors.initials: M
authors.lastname: Hamberg
mesh_terms: D000080:Acetals / Q000737:chemistry / Q000378:metabolism; D000446:Aldehyde-Lyases / Q000235:genetics / Q000378:metabolism*; D028463:Cucumis melo / Q000201:enzymology / Q000235:genetics; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D008401:Gas Chromatography-Mass Spectrometry; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D008041:Linoleic Acids / Q000737:chemistry / Q000378:metabolism; D008054:Lipid Peroxides / Q000737:chemistry / Q000378:metabolism*; D000455:Medicago sativa / Q000201:enzymology / Q000235:genetics; D015394:Molecular Structure; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D031647:Psidium / Q000201:enzymology / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: C506899:9-hydroperoxy-10,12-octadecadienoic acid; D000080:Acetals; D008041:Linoleic Acids; D008054:Lipid Peroxides; D010940:Plant Proteins; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; D000446:Aldehyde-Lyases; C054540:hydroperoxide lyase