SITE-SPECIFIC ISOTOPE FRACTIONATION OF HYDROGEN IN THE BIOSYNTHESIS OF PLANT FATTY-ACIDS

The overall deuterium content of plant lipids has been investigated by isotope ratio mass spectrometry (IRMS), and the site-specific natural isotope fractionation of hydrogen has been studied by H-2-NMR at natu ral abundance (SNIF-NMR). An analytical strategy has been developed in order to exploit the isotopomeric composition determined in clusters associated with different chemical sites of one or several fatty acid components, The method, which combines spectrometric and chromatograph ic data, enables isotopic criteria to be directly derived from raw veg etable oils containing in general two saturated and two unsaturated fa tty acids, These results provide new information on isotopic fractiona tion caused by biochemical, physiological and natural environmental ef fects, Some alternation in the molecular deuterium distribution has be en detected which may be related to the mechanism of fatty acid elonga tion, The successive methylene groups introduced through malonyl CoA a re the subjects of different kinetic isotope effects since one of them is exclusively derived from NADH whereas the other has a contribution from pyruvate, A discriminant analysis of the cluster isotopic parame ters enables several kinds of botanical precursors to be distinguished , The authenticating performances can be improved by taking into accou nt the influence of climatic effects related to the region in which th e plant grew.