| Résumé | The substrate specificity and regioselectivity of the Brassica napus extraplastidial linoleate desaturase (FAD3) was investigated in vivo in a heterologous expression system. A strain of the yeastSaccharomyces cerevisiae producing the plant enzyme was constructed and cultured in media containing a variety of fatty acids. The products of desaturation of these potential substrates were determined by gas chromatographic and mass spectrometric analysis of the yeast cultures. The results indicate that the enzyme has: (a) ω-3, as opposed to Δ-15 or double-bond-related regioselectivity, (b) the ability to desaturate substrates in the 16 to 22 carbon range, (c) a preference for substrates with ω-6 double bonds, but the ability to desaturate substrates with ω-6 hydroxyl groups or ω-9 or ω-5 double bonds, and (d) a relative insensitivity to double bonds proximal to the carboxyl end of the substrate. |
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