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discounted EARLY registration ends Dec 31, 2014
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discounted EARLY registration ends Dec 31, 2014
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
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MetaCyc Pathway: diacylglycerol biosynthesis (PUFA enrichment in oilseed)

Enzyme View:

This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.

Superclasses: Biosynthesis Fatty Acids and Lipids Biosynthesis

Some taxa known to possess this pathway include ? : Arabidopsis thaliana col , Carthamus tinctorius

Expected Taxonomic Range: Spermatophyta

Summary:
Triacyglycerols (TAG) from vegetable oils are a major source of essential fatty acids in human diet, namely polyunsaturated fatty acids (PUFA) linoleate (18:2) and linolenate (18:3). In oilseeds, TAG is synthesized via the Kennedy pathway, where the precursor diacylglycerol (DAG) is de novo synthesized from glycerol-3-phosphate. In addition to the Kennedy pathway, there are several other paths supplying DAG for TAG biosynthesis during seed development in plants [Bates09]. Since further desaturation of 18:1 to form 18:2 and 18:3 occurs mainly in phosphatidylcholine (PC, see phospholipid desaturation), together, these alternative paths in converting PC to DAG can provide enrichment of the PUFA content in TAG.

1) reverse reaction of CDP-choline:1,2-diacylglycerol cholinephosphotransferase (CPT, 2.7.8.2)

Radio tracer studies using microsomes isolated from developing safflower cotyledons indicated that CPT catalyzes a reversible exchange of diacylglycerol moieties between pools of PC and DAG [Slack85]. The maximum activity of CPT coincides with the maximum rate of accumulation of PC and TAG. It is very plausible that the releasing of PUFA-contained DAG from PC, catalyzed by the reverse activity of CPT, may contribute to the enrichment of PUFA in TAG.

2) phosphatidylcholine:diacylglycerol cholinephosphotransferase

A novel enzyme was recently isolated from Arabidopsis [Lu09b]. The Arabidopsis phosphatidylcholine:diacylglycerol cholinephosphotransferase, encoded by ROD1, catalyzes the transfer of phosphocholine head group from PC to DAG. The interconversion of PC and DAG catalyzed by ROD1 provides a major route through which 18:1 (in DAG) enters PC for further desaturation, and in turn the PUFAs 18:2 and 18:3 (in PC) re-enter to the DAG pool for TAG biosynthesis. Arabidopsis ROD1 mutants had a 40% reduction of 18:2 and 18:3 in the seed TAG.

It was postulated that a phospholipase C (3.1.4.3) activity may also generate DAG for TAG synthesis. However no such activity has been reported in developing seeds [Bates09].

Besides the paths depicted here, an acyl editing mechanism also exists that can further enrich PUFA in oilseed TAG [Bates09].

Credits:
Created 06-May-2011 by Zhang P , PMN


References

Bates09: Bates PD, Durrett TP, Ohlrogge JB, Pollard M (2009). "Analysis of acyl fluxes through multiple pathways of triacylglycerol synthesis in developing soybean embryos." Plant Physiol 150(1);55-72. PMID: 19329563

Lu09b: Lu C, Xin Z, Ren Z, Miquel M, Browse J (2009). "An enzyme regulating triacylglycerol composition is encoded by the ROD1 gene of Arabidopsis." Proc Natl Acad Sci U S A 106(44);18837-42. PMID: 19833868

Slack85: Slack CR, Roughan PG, Browse JA, Gardiner SE (1985). "Some properties of cholinephosphotransferase from developing safflower cotyledons." Biochim. Biophys. Acta 833; 438-448.

Other References Related to Enzymes, Genes, Subpathways, and Substrates of this Pathway

Dewey94: Dewey RE, Wilson RF, Novitzky WP, Goode JH (1994). "The AAPT1 gene of soybean complements a cholinephosphotransferase-deficient mutant of yeast." Plant Cell 6(10);1495-507. PMID: 7994181

Goode99: Goode JH, Dewey RE (1999). "Characterization of aminoalcoholphosphotransferases from Arabidopsis thaliana and soybean." Plant Physiol. Biochem. 37(6): 445-457.

Hjelmstad91: Hjelmstad RH, Bell RM (1991). "sn-1,2-diacylglycerol choline- and ethanolaminephosphotransferases in Saccharomyces cerevisiae. Mixed micellar analysis of the CPT1 and EPT1 gene products." J Biol Chem 266(7);4357-65. PMID: 1847919

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."


Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 18.5 on Sun Nov 23, 2014, BIOCYC13B.