A single gene encoding a Delta6-desaturase (FADS2) has been isolated and characterized in mammalian species. This Delta6-desaturase plays a major role in the biosynthesis of PUFAs (polyunsaturated fatty acids). It catalyses the rate-limiting desaturation of linoleic acid (C(18:2) n-6) and alpha-linolenic acid (C(18:3) n-3) required for the biosynthesis of long-chain PUFAs. Moreover, recent studies have provided strong evidence that this Delta6-desaturase also acts on 24-carbon PUFAs of both the n-6 and n-3 series. Another substrate of this Delta6-desaturase has been identified through complementary works from different investigators. This Delta6-desaturase acts on a saturated fatty acid, palmitic acid (C(16:0)), leading to the newly characterized biosynthesis of hexadecenoic acid (C(16:1) n-10) or sapienate.