tailieunhanh - Báo cáo khoa học: Properties of two multifunctional plant fatty acid acetylenase/desaturase enzymes

The properties of theD6 desaturase/acetylenase from the mossCeratodon purpureusand theD12 acetylenase from the dicotCrepis alpinawere studied by expressing the encoding genes inArabidopsis thalianaandSaccharomyces cerevisiae. The acetylenase fromC. alpinaD12 desaturated both oleate and linoleate with about equal efficiency. The desaturation of oleate gave rise to 9(Z),12(E)- and 9(Z),12(Z)-octadeca-dienoates in a ratio of approximately 3 : 1. Experiments using stereospecifically deuterated oleates showed that the pro-Rhydrogen atoms were removed from C-12 and C-13 in the introduction of the 12(Z) double bond, . | Eur. J. Biochem. 271 2991-2997 2004 FEBS 2004 doi Properties of two multifunctional plant fatty acid acetylenase desaturase enzymes Anders S. Carlsson1 Stefan Thomaeus1 Mats Hamberg2 and Sten Stymne1 1 Department of Crop Science Swedish University of Agricultural Sciences Alnarp Sweden department of Medical Biochemistry and Biophysics Division of Physiological Chemistry II Karolinska Institutet Stockholm Sweden The properties of the A6 desaturase acetylenase from the moss Ceratodon purpureus and the A12 acetylenase from the dicot Crepis alpina were studied by expressing the encoding genes in Arabidopsis thaliana and Saccharomyces cerevisiae. The acetylenase from C. alpina A12 desaturated both oleate and linoleate with about equal efficiency. The desaturation of oleate gave rise to 9 Z 12 E - and 9 Z 12 Z -octadeca-dienoates in a ratio of approximately 3 1. Experiments using stereospecifically deuterated oleates showed that the pro-R hydrogen atoms were removed from C-12 and C-13 in the introduction of the 12 Z double bond whereas the pro-R and pro-S hydrogen atoms were removed from these carbons during the formation of the 12 E double bond. The results suggested that the A12 acetylenase could accommodate oleate having either a cisoid or transoid conformation of the C12-C13 single bond and that these conformers served as precursors of the 12 Z and 12 E double bonds respectively. However only the 9 Z 12 Z -octadecadieno-ate isomer could be further desaturated to 9 Z -octadecen-12-ynoate crepenynate by the enzyme. The evolutionarily closely related A12 epoxygenase from Crepis palaestina had only weak desaturase activity but could also produce 9 Z 12 E -octadecadienoate from oleate. The A6 acetyle-nase desaturase from C. purpureus on the other hand produced only the 6 Z isomers using C16 and C18 acyl groups possessing a A9 double bond as substrates. The A6 double bond was efficiently further converted to an acetylenic bond by a second .

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