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Triacylglycerols are synthesised and utilized by transacylation reactions in microsomal preparations of developing safflower ( Carthamus tinctorius L.) seeds

Stobart, K; Mancha, M; Lenman, Marit LU ; Dahlqvist, A and Stymne, S (1997) In Planta 203(1). p.58-66
Abstract
Microsomal membrane preparations from the immature cotyledons of safflower (Carthamus tinctorius) catalysed the interconversion of the neutral lipids, mono-, di-, and triacylglycerol. Membranes were incubated with neutral lipid substrates, 14C-labelled either in the acyl or glycerol moiety, and the incorporation of radioactivity into other complex lipids determined. It was clear that diacylglycerol gave rise to triacylglycerol and monoacylglycerol as well as phosphatidylcholine. Radioactivity from added [14C] triacylglycerol was to a small extent transferred to diacylglycerol whereas added [14C] monoacylglycerol was rapidly converted to diacylglycerols and triacylglycerols. The formation of triacylglycerol from diacylglycerol occurred in... (More)
Microsomal membrane preparations from the immature cotyledons of safflower (Carthamus tinctorius) catalysed the interconversion of the neutral lipids, mono-, di-, and triacylglycerol. Membranes were incubated with neutral lipid substrates, 14C-labelled either in the acyl or glycerol moiety, and the incorporation of radioactivity into other complex lipids determined. It was clear that diacylglycerol gave rise to triacylglycerol and monoacylglycerol as well as phosphatidylcholine. Radioactivity from added [14C] triacylglycerol was to a small extent transferred to diacylglycerol whereas added [14C] monoacylglycerol was rapidly converted to diacylglycerols and triacylglycerols. The formation of triacylglycerol from diacylglycerol occurred in the absence of acyl-CoA and hence did not involve diacylglycerol acyltransferase (DAGAT) activity. Monoacylglycerol was not esterified by direct acylation from acyl-CoA. We propose that these reactions were catalyzed by a diacylglycerol: diacylglycerol transacylase which yielded triacylglycerol and monoacylglycerol, the reaction being freely reversible. The specific activity of the transacylase was some 25% of the diacylglycerol acyltransferase activity and, hence, during the net accumulation of oil, substantial newly formed triacylglycerol equilibrated with the diacylglycerol pool. In its turn the diacylglycerol rapidly interconverted with phosphatidylcholine, the major complex lipid substrate for Δ12 desaturation. Hence, the oleate from triacylglycerols entering phosphatidylcholine via this route could be further desaturated to linoleate. A model is presented which reconciles these observations with our current understanding of fatty acid desaturation in phosphatidylcholine and oil assembly in oleaceous seeds. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Planta
volume
203
issue
1
pages
58 - 66
publisher
Springer
external identifiers
  • scopus:0030802803
ISSN
0032-0935
DOI
10.1007/s004250050165
language
English
LU publication?
no
id
b68853dc-12b3-4a56-bb3c-36a2d7cac076 (old id 1210031)
date added to LUP
2008-08-25 14:03:36
date last changed
2017-07-30 04:38:31
@article{b68853dc-12b3-4a56-bb3c-36a2d7cac076,
  abstract     = {Microsomal membrane preparations from the immature cotyledons of safflower (Carthamus tinctorius) catalysed the interconversion of the neutral lipids, mono-, di-, and triacylglycerol. Membranes were incubated with neutral lipid substrates, 14C-labelled either in the acyl or glycerol moiety, and the incorporation of radioactivity into other complex lipids determined. It was clear that diacylglycerol gave rise to triacylglycerol and monoacylglycerol as well as phosphatidylcholine. Radioactivity from added [14C] triacylglycerol was to a small extent transferred to diacylglycerol whereas added [14C] monoacylglycerol was rapidly converted to diacylglycerols and triacylglycerols. The formation of triacylglycerol from diacylglycerol occurred in the absence of acyl-CoA and hence did not involve diacylglycerol acyltransferase (DAGAT) activity. Monoacylglycerol was not esterified by direct acylation from acyl-CoA. We propose that these reactions were catalyzed by a diacylglycerol: diacylglycerol transacylase which yielded triacylglycerol and monoacylglycerol, the reaction being freely reversible. The specific activity of the transacylase was some 25% of the diacylglycerol acyltransferase activity and, hence, during the net accumulation of oil, substantial newly formed triacylglycerol equilibrated with the diacylglycerol pool. In its turn the diacylglycerol rapidly interconverted with phosphatidylcholine, the major complex lipid substrate for Δ12 desaturation. Hence, the oleate from triacylglycerols entering phosphatidylcholine via this route could be further desaturated to linoleate. A model is presented which reconciles these observations with our current understanding of fatty acid desaturation in phosphatidylcholine and oil assembly in oleaceous seeds.},
  author       = {Stobart, K and Mancha, M and Lenman, Marit and Dahlqvist, A and Stymne, S},
  issn         = {0032-0935},
  language     = {eng},
  number       = {1},
  pages        = {58--66},
  publisher    = {Springer},
  series       = {Planta},
  title        = {Triacylglycerols are synthesised and utilized by transacylation reactions in microsomal preparations of developing safflower ( Carthamus tinctorius L.) seeds},
  url          = {http://dx.doi.org/10.1007/s004250050165},
  volume       = {203},
  year         = {1997},
}