TRIACYLGLYCEROL BIOSYNTHESIS IN DEVELOPING SEEDS OF TROPAEOLUM-MAJUS L AND LIMNANTHES-DOUGLASII R BR
TRIACYLGLYCEROL BIOSYNTHESIS IN DEVELOPING SEEDS OF TROPAEOLUM-MAJUS L AND LIMNANTHES-DOUGLASII R BR
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DOI：
10.1007/bf00216816
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发表时间：
1992-09-01
期刊：
影响因子：
4.3
通讯作者：
FRENTZEN, M
中科院分区：
文献类型：
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作者：
LOHDEN, I;FRENTZEN, M
大对流层蝗和道格拉斯蝗的三酰基甘油。在甘油主链的每个位置主要与长链酰基酯化。为了阐明这些酰基是否通过甘油-3-磷酸的逐步酰化直接转化为三酰基甘油，研究了两种植物的发育胚胎中种子油的形成。[1-C-14]利用不同发育阶段的胚胎进行醋酸标记实验，以及测定微体酰基辅酶a:sn-甘油-3-磷酸酰基转移酶（EC 2.3.1.15）和酰基辅酶a:sn-1-酰基甘油-3-磷酸酰基转移酶（EC 2.3.1.51）的性质，揭示了两种植物物种之间的差异，特别是在三酰基甘油C2位置上的超长链酰基结合方面。在道格拉斯L.发育中的胚胎微粒体中，检测到一种以长链酰基辅酶a硫酯为底物的甘油-3-磷酸和一种酰基甘油-3-磷酸酰基转移酶。因此，在L. douglasii种子中，在从头合成过程中，非常长的链酰基不仅可以进入三酰基甘油的C1位置，还可以进入C2位置。将发育中的胚胎酰基转移酶的性质与叶片相应活性的性质进行比较，发现道格拉斯L.在胚胎中特异性表达了一种依赖于e酰辅酶A的微粒体1-酰基甘油-3-磷酸酰基转移酶。大鼠发育胚胎微粒体甘油-3-磷酸酰基转移酶的活性与道格拉斯乳杆菌的活性非常相似。另一方面，这两种植物的微粒体1-酰基甘油-3-磷酸酰基转移酶表现出明显不同的底物特异性。不管1-酰基甘油-3-磷酸的酰基是什么，也不管酰基辅酶a硫酯是单独提供还是混合提供，与道格拉斯L.相比，马氏T.的酶对戊酰辅酶a没有活性。这些酶的研究结果与[1-C-14]乙酸标记实验的结果吻合得很好，因此表明T. majus已经发展出与L. douglasii不同的机制，将芥酸结合到其三酰基甘油的C2位置。
Triacylglycerols of both Tropaeolum majus L. and Limnanthes douglasii R. Br. are predominantly esterified with very long-chain acyl groups at each position of the glycerol backbone. In order to elucidate whether these acyl groups are directly chanelled into the triacylglycerols via the stepwise acylation of glycerol-3-phosphate, seed oil formation has been investigated in developing embryos of both plant species. [1-C-14]Acetate labelling experiments using embryos at different stages of development, as well as the determination of the properties of the microsomal acyl-CoA: sn-glycerol-3-phosphate acyltransferase (EC 2.3.1.15) and acyl-CoA:sn-1-acylglycerol-3-phosphate acyltransferase (EC 2.3.1.51), revealed differences between the two plant species, especially with respect to the incorporation of very long-chain acyl groups into the C2 position of the triacylglycerols. In microsomal fractions of developing embryos of L. douglasii both a glycerol-3-phosphate and a I-acylglycerol-3-phosphate acyltransferase were detected which utilize very long-chain acyl-CoA thioesters as substrates. Thus, in seeds of L. douglasii very long-chain acyl groups can enter not only the C1, but also the C2 position of the triacylglycerols in the course of de-novo biosynthesis. A comparison of the properties of the acyltransferases of developing embryos with those of the corresponding activities of leaves indicates an embryo specific expression of an erucoyl-CoA-dependent microsomal 1-acylglycerol-3-phosphate acyltransferase in L. douglasii. The microsomal glycerol-3-phosphate acyltransferase of developing embryos of T. majus displayed properties very similar to those of the corresponding activity of L. douglasii. On the other hand, the microsomal 1-acylglycerol-3-phosphate acyltransferases of the two plant species showed strikingly different substrate specificities. Irrespective of the acyl groups of 1-acylglycerol-3-phosphate and regardless of whether acyl-CoA thioesters were offered separately or in mixtures, the enzyme of T. majus, in contrast to that of L. douglasii, was inactive with erucoyl-CoA. These results of the enzyme studies correspond well with those of the [1-C-14]acetate labelling experiments and thus indicate that T. majus has developed mechanisms different from those of L. douglasii for the incorporation of erucic acid into the C2 position of its triacylglycerols.