Elongation of (n?9) and (n?7)cis-monounsaturated and saturated fatty acids in seeds ofsinapis alba |
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Authors: | Kumar D Mukherjee |
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Affiliation: | (1) Bundesanstalt für Fettforschung, Piusallee 68/76, D-4400 Münster, Federal Republic of Germany |
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Abstract: | Lipids in developing seeds ofSinapis alba contain appreciable proportions of (n−7)octadecenoic (vaccenic) acid besides its (n−9) isomer (oleic acid), whereas the constituent
very long chain (>C18) monounsaturated fatty acids of these lipids are overwhelmingly composed of the (n−9) isomers. Cotyledons of developingSinapis alba seed use 1-14C]acetate, 1-14C]malonate or 1,3-14C]malonyl-CoA for de novo synthesis of palmitic, stearic and oleic acids and for elongation of preformed oleic, vaccenic and
stearic acids to their higher (n−9), (n−7) and saturated homologs, respectively. Moreover, elongation of preformed (n−7)palmitoleic
acid to vaccenic acid is observed. Stepwise C2-additions to preformed oleoyl-CoA by acetyl-CoA or malonyl-CoA yielding (n−9)icosenoyl-CoA, (n−9)docosenoyl-CoA and (n−9)tetracosenoyl-CoA
are by far the most predominant reactions catalyzed by the elongase system, which seems to have a preference for oleoyl-CoA
over vaccenoyl-CoA as the primer. The pattern of14C-labeling of the very long chain fatty acids formed from either acetate or malonate shows a close analogy in the mode of
elongation of monounsaturated and saturated fatty acids. |
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