Nutritional regulation of yeast delta-9 fatty acid desaturase activity

Abstract

The addition of unsaturated fatty acids to cultures of Saccharomyces cerevisiae significantly altered the microsomal lipid composition. Supplementation with either of the naturally occurring palmitoleic (16:1) or oleic (18:1) acids caused increased levels in membrane phospholipids and reduced levels of the complementary acid. Growth in the presence of equimolar quantities of 16:1 and 18:1 acids, however, produced a fatty acid composition similar to that found in unsupplemented cell membranes. Linoleic acid (18:2) was not found in S. cerevisiae grown under normal conditions. It was preferentially internalized and incorporated into microsomes, however, at levels exceeding 50% of the total fatty acid species. This resulted in an almost total loss of 16:1 and a reduction of 18:1 to 25% of its normal level. The A-9 fatty acid desaturase, a microsomal enzyme that forms 16:1 and 18:1 from saturated acyl coenzyme A precursors, was affected by the presence of exogenous fatty acids. Enzyme activity toward the 16:0 coenzyme A substrate was elevated in microsomes from saturated-fattyacid-supplemented cultures and sharply repressed following the addition of unsaturated fatty acids, including 18:2. Northern (RNA blot) and slot-blot analyses of mRNA encoded by the OLE] gene, which appears to be the structural gene for the A-9 desaturase, indicated that it was sharply reduced in unsaturated-fatty-acid-fed cells. These data suggest that a significant part of the regulation involves modulation of available transcripts.Approximately 70% of the fatty acids in membrane lipids of the yeast Saccharomyces cerevisiae consist of palmitoleic acid (16:1) and oleic acid (18:1) (12). The remaining fatty acids are saturated, consisting primarily of palmitic acid (16:0) and lesser amounts of stearic acid (18:0) and myristic acid (14:0). Unlike most other fungi, whose most abundant unsaturated fatty acids are the di-and trienoic linoleic (18:2) and ox-linolenic (18:3) species (27), S. cerevisiae synthesizes only monounsaturated acids when grown under normal laboratory conditions. Unsaturated fatty acids are synthesized in fungal and animal cells by fatty acid desaturases, which are hydrophobic microsomal enzymes (3,4,23). The A-9 desaturase catalyzes the formation of the initial double bond between the 9th and 10th carbons of both palmitoyl (16:0) and stearoyl (18:0) coenzyme A (CoA) substrates to make 16:1 and 18:1. Introduction of the double bond is a complex reaction requiring the removal of electrons and hydrogens from the hydrocarbon chain of the fatty acid and the transfer of an additional two electrons from NADH to molecular oxygen via cytochrome b5 and b5 reductase (4,22).Considerable evidence has accumulated showing that the A-9 fatty acid desaturase in animal cells is regulated by dietary fatty acids. For example, in rat and chicken liver (18,19,25), the enzyme is repressed by dietary unsaturated fatty acids. The desaturase is the only component of the enzyme system that appears to be regulated, however, since cytochrome b5 and b5 red...

Oxygen-dependent low-temperature 12 (n6)-desaturase induction and alteration of fatty acid composition in Acanthamoeba castellanii

“…The alternative possibility that oxygen-o r nitrogen-induced covalent modification altered the relative proportion of 'active' enzyme can be discounted here. Firstly, no such mechanism has been reported for desaturases, where regulation is generally considered to occur at the transcriptional o r translational level (Bossie & Martin, 1989;McDonough e t al., 1992;Vigh e t al., 1993). Moreover, it was found that cells which were transiently exposed to elevated oxygen, by chilling cultures just prior to sparging with nitrogen, still displayed considerably higher desaturase activity 1 h later than cells chilled after exposure to nitrogen.…”

“…In Saccharomyces cerevisiae, supplementation of growth media with unsaturated fatty acids resulted in a decline in transcription of the desaturase gene (Bossie & Martin, 1989) ; the specificity of this response to particular fatty acid species suggested that regulation was initiated by fatty acid binding to a transcriptional sensor, rather than by changes in membrane order (McDonough e t al., 1992). In the cyanobacterium S'nechoystis PCC 6803, increases in the degree of plasma-membrane fatty acid saturation, brought about by palladium-catalysed hydrogenation, resulted in enhanced transcription of the desA gene encoding the Al2-desaturase in a similar fashion to low-temperature induction (Vigh e t al., 1993 ;Murata, 1994).…”

Dosage-dependent functions of fatty acid desaturase Ole1p in growth and morphogenesis of Candida albicans

“…OLE1 expression is regulated by fatty acids, oxygen and temperature. Saturated fatty acids induce a 1?6-fold increase in transcription, while unsaturated fatty acids repress OLE1 transcription up to 60-fold (McDonough et al, 1992;Bossie & Martin, 1989). At low temperatures and during oxygen limitation, OLE1 expression is induced (Kwast et al, 1998;Nakagawa et al, 2002).…”

Lipid-dependent Subcellular Relocalization of the Acyl Chain Desaturase in Yeast

“…Desaturation is catalyzed by a single essential ⌬-9 desaturase encoded by the OLE1 gene (Stukey et al, 1989(Stukey et al, , 1990. The activity of the desaturase is tightly regulated at several different levels by UFA levels (Bossie and Martin, 1989). For example, steady state levels of OLE1 mRNA sharply decline upon addition of UFAs by a mechanism that is sensitive to the position of the double bond and that involves both transcriptional and posttranscriptional regulation of OLE1 mRNA synthesis and stability (McDonough et al, 1992;Gonzalez and Martin, 1996;Choi et al, 1996).…”