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.
Microsomes isolated from the developing cotyledons of the seeds of the safflower varieties, very-high-linoleate, Gila and high-oleate, were capable of exchanging the acyl groups in acyl-CoA with the fatty acids in position 2 of phosphatidylcholine. The specificity of the 'acyl-exchange' towards the acyl moiety in acyl-CoA was selective in the order: oleate greater than linoleate greater than linolenate. Stearoyl-CoA was completely selected against when presented in a mixed substrate with unsaturated 18-carbon acyl-CoAs. Microsomes, of the very-high-linoleate safflower variety, rapidly desaturated in situ-labelled [14C]oleoylphosphatidylcholine in the presence of NADH. Little oleate desaturation, however, was observed in the microsomes of the high-oleate variety. Microsomes of the Gila and high-oleate varieties of safflower rapidly synthesised phosphatidic acid by the acylation of glycerol 3-phosphate with acyl-CoA. The phosphatidic acid was metabolised to diacylglycerol, which was further acylated to triacylglycerol. A strong selectivity for linoleoyl-CoA was found for the acylation of glycerol 3-phosphate in both the Gila and high-oleate microsomes. On the basis of these results, we propose that the pattern of 18-carbon unsaturated fatty acids in the triacylglycerols of all 'oil'-producing seeds is a direct reflection of the fatty acids in the acyl-CoA pool. This, in turn, is governed by: A, the rate and specificity of the acyl exchange between acyl-CoA and phosphatidylcholine; B, the rate of oleate (and linoleate) desaturation in phosphatidylcholine; and C, the rate and specificity of the glycerophosphate acyltransferase.
D000214:Acyl Coenzyme A / Q000378:metabolism*; D000215:Acylation; D055598:Chemical Phenomena; D002621:Chemistry; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D008861:Microsomes / Q000378:metabolism; D010945:Plants, Edible / Q000378:metabolism*; D012639:Seeds; D014280:Triglycerides / Q000096:biosynthesis*
D000214:Acyl Coenzyme A; D005231:Fatty Acids, Unsaturated; D014280:Triglycerides