Natural deuterium distribution in long-chain fatty acids is nonstatistical: a site-specific study by quantitative (2)H NMR spectroscopy.

Quantitative (2)H NMR spectroscopy has been used to study the site-specific natural occurrence of (2)H in common unsaturated fatty acids. A marked nonstatistical isotopic distribution of (2)H is observed in both methyl oleate and methyl linoleate. By chemical modification, the internal isotopic (2)H signatures of these products have been partially accessed. Notably, it can be seen that (1) the sites of desaturation show a strong impoverishment at only one ethylenic position of each desaturation; (2) the level of impoverishment reflects the source of the hydrogen atoms present; and (3) a gradient of (2)H content occurs along the chain. These effects can in part be related to the mechanisms proposed for the enzymes responsible for the various steps of biosynthesis of unsaturated fatty acids in plants.