Biosynthesis of gamma-linolenic acid in cotyledons and microsomal preparations of the developing seeds of common borage (Borago officinalis).
Abstract
The developing seeds of Borago officinalis (common borage) accumulate a triacylglycerol oil that is relatively rich in the uncommon fatty acid gamma-linolenate (octadec-6,9,12-trienoic acid). Incubation of developing, whole, cotyledons with [14C]oleate and [14C]linoleate showed that the gamma-linolenate was synthesized by the sequential desaturation of oleate----linoleate----gamma-linolenate. Microsomal membrane preparations from the developing cotyledons contained an active delta 6-desaturase enzyme that catalysed the conversion of linoleate into gamma-linolenate. Experiments were designed to manipulate the [14C]linoleate content of the microsomal phosphatidylcholine. The [14C]linoleoyl phosphatidylcholine labelled in situ was converted into gamma-linolenoyl phosphatidylcholine in the presence of NADH. The substrate for the delta 6-desaturase in borage was, therefore, the linoleate in the complex microsomal lipid phosphatidylcholine, rather than, as in animals, the acyl-CoA. This was further confirmed in experiments that compared the specific radioactivity of the gamma-linolenate, in acyl-CoA and phosphatidylcholine, that was synthesized when [14C]linoleoyl-CoA was incubated with microsomal membranes, NADH and non-radioactive gamma-linolenoyl-CoA. The delta 6-desaturase was positionally specific and only utilized the linoleate in position 2 of sn-phosphatidylcholine. Analysis of the positional distribution of fatty acids in the endogenous microsomal sn-phosphatidylcholine showed that, whereas position 1 contained substantial linoleate, only small amounts of gamma-linolenate were present. The results shed further light on the synthesis of C18 polyunsaturated fatty acids in plants and in particular its relationship to the regulation of the acyl quality of the triacylglycerols in oilseeds.
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- BLIGH EG, DYER WJ. A rapid method of total lipid extraction and purification. Can J Biochem Physiol. 1959 Aug;37(8):911–917. [PubMed] [Google Scholar]
- Brenner RR. Nutritional and hormonal factors influencing desaturation of essential fatty acids. Prog Lipid Res. 1981;20:41–47. [PubMed] [Google Scholar]
- Griffiths G, Stobart AK, Stymne S. The acylation of sn-glycerol 3-phosphate and the metabolism of phosphatidate in microsomal preparations from the developing cotyledons of safflower (Carthamus tinctorius L.) seed. Biochem J. 1985 Sep 1;230(2):379–388.[PMC free article] [PubMed] [Google Scholar]
- Hawke JC, Stumpf PK. The incorporation of oleic and linoleic acids and their desaturation products into the glycerolipids of maize leaves. Arch Biochem Biophys. 1980 Aug;203(1):296–306. [PubMed] [Google Scholar]
- Holman RT, Johnson S. Changes in essential fatty acid profile of serum phospholipids in human disease. Prog Lipid Res. 1981;20:67–73. [PubMed] [Google Scholar]
- Howling D, Morris LJ, Gurr MI, James AT. The specificity of fatty acid desaturases and hydroxylases. The dehydrogenation and hydroxylation of monoenoic acids. Biochim Biophys Acta. 1972 Jan 27;260(1):10–19. [PubMed] [Google Scholar]
- Jones AV, Harwood JL. Desaturation of linoleic acid from exogenous lipids by isolated chloroplasts. Biochem J. 1980 Sep 15;190(3):851–854.[PMC free article] [PubMed] [Google Scholar]
- KATES M. SIMPLIFIED PROCEDURES FOR HYDROLYSIS OR METHANOLYSIS OF LIPIDS. J Lipid Res. 1964 Jan;5:132–135. [PubMed] [Google Scholar]
- Murphy DJ, Woodrow IE, Mukherjee KD. Substrate specificities of the enzymes of the oleate desaturase system from photosynthetic tissue. Biochem J. 1985 Jan 1;225(1):267–270.[PMC free article] [PubMed] [Google Scholar]
- Roughan PG, Mudd JB, McManus TT, Slack CR. Linoleate and alpha-linolenate synthesis by isolated spinach (Spinacia oleracea) chloroplasts. Biochem J. 1979 Dec 15;184(3):571–574.[PMC free article] [PubMed] [Google Scholar]
- Sánchez M, Nicholls DG, Brindley DN. [The relationship between palmitoyl-coenzyme A synthetase activity and esterification of sn-glycerol 3-phosphate in rat liver mitochondria]. Biochem J. 1973 Apr;132(4):697–706.[PMC free article] [PubMed] [Google Scholar]
- Slack CR, Roughan PG, Browse J. Evidence for an oleoyl phosphatidylcholine desaturase in microsomal preparations from cotyledons of safflower (Carthamus tinctorius) seed. Biochem J. 1979 Jun 1;179(3):649–656.[PMC free article] [PubMed] [Google Scholar]
- Stobart AK, Stymne S. The interconversion of diacylglycerol and phosphatidylcholine during triacylglycerol production in microsomal preparations of developing cotyledons of safflower (Carthamus tinctorius L.). Biochem J. 1985 Nov 15;232(1):217–221.[PMC free article] [PubMed] [Google Scholar]
- Stymne S, Appelqvist LA. The biosynthesis of linoleate from oleoyl-CoA via oleoyl-phosphatidylcholine in microsomes of developing safflower seeds. Eur J Biochem. 1978 Oct;90(2):223–229. [PubMed] [Google Scholar]
- Stymne S, Stobart AK. Evidence for the reversibility of the acyl-CoA:lysophosphatidylcholine acyltransferase in microsomal preparations from developing safflower (Carthamus tinctorius L.) cotyledons and rat liver. Biochem J. 1984 Oct 15;223(2):305–314.[PMC free article] [PubMed] [Google Scholar]
- Stymne S, Stobart AK. The biosynthesis of triacylglycerols in microsomal preparations of developing cotyledons of sunflower (Helianthus annuus L.). Biochem J. 1984 Jun 1;220(2):481–488.[PMC free article] [PubMed] [Google Scholar]
- Stymne S, Stobart AK. Involvement of acyl exchange between acyl-CoA and phosphatidylcholine in the remodelling of phosphatidylcholine in microsomal preparations of rat lung. Biochim Biophys Acta. 1985 Dec 4;837(3):239–250. [PubMed] [Google Scholar]
- Stymne S, Stobart AK, Glad G. The role of the acyl-CoA pool in the synthesis of polyunsaturated 18-carbon fatty acids and triacylglycerol production in the microsomes of developing safflower seeds. Biochim Biophys Acta. 1983 Jul 12;752(2):198–208. [PubMed] [Google Scholar]
- Traitler H, Winter H, Richli U, Ingenbleek Y. Characterization of gamma-linolenic acid in Ribes seed. Lipids. 1984 Dec;19(12):923–928. [PubMed] [Google Scholar]