scholarly journals Inhibition of the glucose-6-phosphate transporter in oilseed rape (Brassica napus L.) plastids by acyl-CoA thioesters reduces fatty acid synthesis

2000 ◽  
Vol 352 (2) ◽  
pp. 525-532 ◽  
Author(s):  
Simon R. FOX ◽  
Lionel M. HILL ◽  
Stephen RAWSTHORNE ◽  
Matthew J. HILLS
Keyword(s):  
Fatty Acid ◽  
Brassica Napus ◽  
Oilseed Rape ◽  
Acid Synthesis ◽  
Brassica Napus L ◽  
Coa Ligase ◽  
Chain Acyl ◽  
Coa Thioesters ◽  
Long Chain

Addition of oleoyl-CoA (1µM), or other acyl-CoA thioesters with a chain length of C16 or greater, to oilseed rape plastids (Brassica napus L.) inhibited the rate of D-glucose 6-phosphate (Glc6P) uptake by 70% after 2min. The IC50 value for oleoyl-CoA inhibition of the transporter was approx. 0.2–0.3µM. Inhibition was alleviated by the addition of acyl-CoA binding protein (ACBP) or BSA at slightly higher concentrations. Oleic acid (5–25µM), Tween 40 (10µM), Triton-X 100 (10µM) and palmitoylcarnitine (5µM) had no effect on Glc6P uptake. The uptake of [1-14C]Glc6P occurred in exchange for Pi, 3-phosphoglycerate or Glc6P at a typical rate of 30nmol Glc6P/min per unit of glyceraldehyde-3-phosphate dehydrogenase (NADP+). The Km(app) of the Glc6P transporter for Glc6P was 100µM. Neither CoA (0.3mM) nor ATP (3mM) inhibited Glc6P uptake, but the transporter was inhibited by 72% when ATP and CoA were added together. This inhibition was attributable to the synthesis of acyl-CoA thioesters, predominantly oleoyl-CoA and palmitoyl-CoA, by long-chain fatty acid-CoA ligase (EC 6.2.1.3) from endogenous fatty acids in the plastid preparations. Acyl-CoA thioesters did not inhibit the uptake of [2-14C]pyruvate or D-[1-14C]glucose into plastids. In vivo quantities of oleoyl-CoA and other long-chain acyl-CoA thioesters were lower than those for ACBP in early cotyledonary embryos, 0.7±0.2pmol/embryo and 2.2±0.2pmol/embryo respectively, but in late cotyledonary embryos quantities of long-chain acyl-CoA thioesters were greater than ACBP, 3±0.4pmol/embryo and 1.9±0.2pmol/embryo respectively.

The role of plastidial transporters in developing embryos of oilseed rape (Brassica napus L.) for fatty acid synthesis

2000 ◽  
Vol 28 (6) ◽  
pp. 665-666 ◽  
Author(s):  
S. E. Kubis ◽  
S. Rawsthorne
Keyword(s):  
Fatty Acid ◽  
Brassica Napus ◽  
Oilseed Rape ◽  
Fatty Acid Synthesis ◽  
Developmental Stages ◽  
Acid Synthesis ◽  
Brassica Napus L

The phosphoenolpyruvate transporter (PPT) is one of several important transporters for channelling carbon intermediates utilized for fatty acid synthesis and other plastidial pathways from the cytosol into the plastid. In this paper we show results on how the activity of the PPT changes between two important, physiologically different developmental stages of oilseed rape embryos.

scholarly journals Inhibition by long-chain acyl-CoAs of glucose 6-phosphate metabolism in plastids isolated from developing embryos of oilseed rape (Brassica napus L.)

2000 ◽  
Vol 348 (1) ◽  
pp. 145-150 ◽  
Author(s):  
Philip E. JOHNSON ◽  
Simon R. FOX ◽  
Matthew J. HILLS ◽  
Stephen RAWSTHORNE
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
De Novo ◽  
Starch Synthesis ◽  
Acid Synthesis ◽  
Pentose Phosphate ◽  
Pyruvate Metabolism ◽  
Brassica Napus L ◽  
Chain Acyl ◽  
Long Chain

The effects of long-chain acyl-CoA (lcACoA) esters (both added exogenously and synthesized de novo) and acyl-CoA binding protein (ACBP) on plastidial glucose 6-phosphate (Glc6P) and pyruvate metabolism were examined using isolated plastids. The binding of lcACoA esters by ACBP stimulated the utilization of Glc6P for fatty acid synthesis, starch synthesis and reductant supply via the oxidative pentose phosphate (OPP) pathway. Stimulation occurred at low (1-10 μM) concentrations of ACBP. Pyruvate-dependent fatty acid synthesis was not directly affected by ACBP. However, addition of ACBP did increase the Glc6P-dependent stimulation of pyruvate utilization mediated through the OPP pathway. On the basis of these experiments, we conclude that lcACoA esters may inhibit Glc6P uptake into plastids, and that this inhibition is relieved by ACBP. We also suggest that utilization of other substrates for fatty acid synthesis may be affected by lcACoA/ACBP via their effects on the OPP pathway.

Substrate preferences of long-chain acyl-CoA synthetase and diacylglycerol acyltransferase contribute to enrichment of flax seed oil with α-linolenic acid

2018 ◽  
Vol 475 (8) ◽  
pp. 1473-1489 ◽  
Author(s):  
Yang Xu ◽  
Roman Holic ◽  
Darren Li ◽  
Xue Pan ◽  
Elzbieta Mietkiewska ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Linolenic Acid ◽  
Seed Oil ◽  
Diacylglycerol Acyltransferase ◽  
Acyl Donor ◽  
Flax Seed ◽  
Chain Acyl ◽  
Long Chain

Seed oil from flax (Linum usitatissimum) is enriched in α-linolenic acid (ALA; 18:3Δ9cis,12cis,15cis), but the biochemical processes underlying the enrichment of flax seed oil with this polyunsaturated fatty acid are not fully elucidated. Here, a potential process involving the catalytic actions of long-chain acyl-CoA synthetase (LACS) and diacylglycerol acyltransferase (DGAT) is proposed for ALA enrichment in triacylglycerol (TAG). LACS catalyzes the ATP-dependent activation of free fatty acid to form acyl-CoA, which in turn may serve as an acyl-donor in the DGAT-catalyzed reaction leading to TAG. To test this hypothesis, flax LACS and DGAT cDNAs were functionally expressed in Saccharomyces cerevisiae strains to probe their possible involvement in the enrichment of TAG with ALA. Among the identified flax LACSs, LuLACS8A exhibited significantly enhanced specificity for ALA over oleic acid (18:1Δ9cis) or linoleic acid (18:2Δ9cis,12cis). Enhanced α-linolenoyl-CoA specificity was also observed in the enzymatic assay of flax DGAT2 (LuDGAT2-3), which displayed ∼20 times increased preference toward α-linolenoyl-CoA over oleoyl-CoA. Moreover, when LuLACS8A and LuDGAT2-3 were co-expressed in yeast, both in vitro and in vivo experiments indicated that the ALA-containing TAG enrichment process was operative between LuLACS8A- and LuDGAT2-3-catalyzed reactions. Overall, the results support the hypothesis that the cooperation between the reactions catalyzed by LACS8 and DGAT2 may represent a route to enrich ALA production in the flax seed oil.

Sign in / Sign up

Export Citation Format

Share Document