Application of a GC-MS method using deuterated fatty acids for tracingcis-vaccenic acid biosynthesis in kaki pulp |
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Authors: | Akira Shibahara Kohei Yamamoto Mariko Takeoka Akemi Kinoshita Goro Kajimoto Takao Nakayama Manjiro Noda |
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Affiliation: | (1) Department of Nutrition, Kobe-Gakuin University, Arise, Ikawadani-cho, Nishi-ku, 673 Kobe, Japan;(2) General Testing Research Institute of Japan Oil Stuff Inspectors’ Corporation, Mikagetsuka-machi, Higashinada-ku, 658 Kobe, Japan;(3) Department of Agricultural Chemistry, Kinki University, Kowakae, 577 Higashiosaka, Japan |
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Abstract: | A gas chromatographic-mass spectrometric method using 2,2-2H2]fatty acids has been developed to trace the biosynthesis ofcis-vaccenic (cis-11-octadecenoic) acid in higher plants. The deuterated fatty acids and other unlabeled fatty acids in the biosynthetic reaction
mixture were converted into bis(methylthio) derivatives and analyzed by mass chromatography. The principle of this method
was based on the shift of key fragment ions (containing two deuterium atoms) due to the cleavage between the methylthio-substituted
carbons. The labeled compounds were detected by the m/z values which shifted 2 mass units from those of the corresponding
unlabeled compounds and estimated by a calibration curve based on the peak areas of the key fragment ions. For metabolic experiments,
a homogenate fraction was prepared from the pulp part of maturing kaki (Diospyros kaki) fruit and incubated with ammonium 2,2-2H2]palmitoleate (cis-9-hexadecenoate) or 2,2-2H2]palmitoleoyl-CoA. The incubation resulted in the formation of detectable amounts of isotopically-labeledcis-vaccenic acid containing two deuterium atoms at the carbon chain between the double bond and the carboxyl group. This experimental
evidence proved thatcis-vaccenic acid was formed from palmitoleic acid by chain elongation. |
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