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Resumen:
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A range ofcis- andtrans-monoenoic fatty acids was tested as substrates for desaturation in microsomal preparations from rat liver.Trans-monoenoic acids were generally desaturated in the 9 position to the same extent as stearic acid. Acids with 7-trans- and 11-trans-olefinic unsaturation produced 7-trans,9-cis- and 9-cis,11-trans-conjugated dienoic acids, respectively, but the 8-trans- and 10-trans-monoenoic acids did not give 8,9- or 9,10-allenes. Of thecis-monoenoic acids examined, only those with double bonds at or beyond the 14 position gave any measurable 9 desaturation. When 9 desaturation of long chain saturated acids was inhibited by adding sterculic acid, these saturated acids were desaturated at the 5 and 6 positions. Many of the monoenoic acids tested were also desaturated at the 5 and/or 6 positions, although the percentage conversions were always low. 9-cis,11-trans-, 9-cis,12-trans- and 9-cis,13-trans-dienoic acids, produced in situ by 9 desaturation of the corresponding monoenoic acids, were extensively desaturated in the 6 position. These results are discussed in terms of: (a) the various models proposed to explain the substrate specificities of the desaturases, and (b) the metabolism of unnatural fatty acids ingested from dietary sources.
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