Desaturation of positional and geometric isomers of monoenoic fatty acids by microsomal preparations from rat liver.
A range of cis- and trans-monoenoic fatty acids was tested as substrates for desaturation in microsomal preparations from rat liver. Trans-monoenoic acids were generally desaturated in the delta 9 position to the same extent as stearic acid. Acids with delta 7-trans- and delta 11-trans-olefinic unsaturation produced delta 7-trans, 9-cis- and delta 9-cis, 11-trans-conjugated dienoic acids, respectively, but the delta 8-trans-and delta 10-trans-monoenoic acids did not give delta 8,9- or delta 9,10-allenes. Of the cis-monoenoic acids examined, only those with double bonds at or beyond the delta 14 position gave any measurable delta 9 desaturation. When delta 9 desaturation of long chain saturated acids was inhibited by adding sterculic acid, these saturated acids were desaturated at the delta 5 and delta 6 positions. Many of the monoenoic acids tested were also desaturated at the delta 5 and/or delta 6 positions, although the percentage conversions were always low. delta 9-cis, 11-trans-, delta 9-cis, 12-trans- and delta 9-cis, 13-trans-dienoic acids, produced in situ by delta 9 desaturation of the corresponding monoenoic acids, were extensively desaturated in the delta 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.
D000818:Animals; D003521:Cyclopropanes / Q000494:pharmacology; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated / Q000378:metabolism* / Q000494:pharmacology; D007536:Isomerism; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D013379:Substrate Specificity
D003521:Cyclopropanes; D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated; D044943:Fatty Acid Desaturases; C003345:sterculic acid