ACQUISITION OF MEMBRANE-LIPIDS BY DIFFERENTIATING GLYOXYSOMES - ROLE OF LIPID BODIES
ACQUISITION OF MEMBRANE-LIPIDS BY DIFFERENTIATING GLYOXYSOMES - ROLE OF LIPID BODIES
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DOI：
10.1083/jcb.115.4.995
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发表时间：
1991-11-01
影响因子：
7.8
通讯作者：
TRELEASE, RN
中科院分区：
文献类型：
--
作者：
CHAPMAN, KD;TRELEASE, RN
棉花(Gossypium hirsutom，L.)幼苗在种子吸胀后48小时内显著扩大(KUNCE，C.M.，R.N.T Release和D.C.Doman)。1984年。车前草(Planta(Berl.)161：156-164)，以实现储存的棉籽油的动员。我们发现，在所研究的所有阶段的扩大乙氧基体膜含有很大比例(按重量计36-62%)的非极性脂类，几乎全部是三酰甘油(TAG)和TAG代谢物。游离脂肪酸在这些非极性脂肪中所占的比例最大。6种不常见(且尚未鉴定)的脂肪酸构成了乙醛体膜标签中游离脂肪酸和脂肪酸的大部分(51%)；同样的6种不常见脂肪酸在棉籽贮藏脂体标签中的酰基成分中占7%。脂体标记主要由棕榈酸、油酸和亚油酸组成(合计占70%)。这三种主要储存脂肪酸占糖氧体膜标签中游离脂肪酸和脂肪酸的10%，其中磷脂酰胆碱(PC)和磷脂酰乙醇胺(PE)是糖氧体膜磷脂的主要成分(重量比为61%)。体内脉冲示踪实验清楚地表明，C-14-胆碱和C-14-乙醇胺分别在子叶的内质网合成了C-14-PC和C-14-PE，并被转运到线粒体，但这些脂质不被转运到扩大的乙氧基体。由于内质网在糖体膜磷脂合成中的缺失，以及脂体与乙氧体膜在脂组成上的相似性，我们提出并检验了一种新的假说，即脂体作为扩大糖体膜扩张的非极性脂和磷脂的动态来源。在无细胞体系中，H-3-三酸甘油酯(TO)和H-3-PC确实从脂体转移到乙氧基体。在体外，H-3-PC也转移到线粒体，而不是H-3-TO。脂质转移量随时间和受体细胞器蛋白的量呈线性增加，只有当脂质体膜蛋白与供体脂体结合时才发生转移。将H-3-TO转移到乙氧基体膜上，并结合到乙氧基体膜上，然后将H-3-TO水解为游离脂肪酸。H-3-PC被转移到乙氧基体膜和线粒体膜上，没有随后的水解酶。我们的数据与ER在萌发后的幼苗生长过程中为乙氧基体膜贡献膜脂的假设不一致。相反，这些数据支持乙氧基体(过氧化体)膜脂的一种新来源；储存在异养幼苗生长过程中转化为碳水化合物的储存脂的脂体也为扩大的乙氧体提供非极性脂和磷脂，以适应膜的扩张。提出了一个描述棉籽乙二氧基体膜脂来源和细胞内转运的工作模型。
Glyoxysomes in cotyledons of cotton (Gossypium hirsutum, L.) seedlings enlarge dramatically within 48 h after seed imbibition (Kunce, C. M., R. N. Trelease, and D. C. Doman. 1984. Planta (Berl.). 161:156-164) to effect mobilization of stored cotton-seed oil. We discovered that the membranes of enlarging glyoxysomes at all stages examined contained a large percentage (36-62% by weight) of nonpolar lipid, nearly all of which were triacylglycerols (TAGs) and TAG metabolites. Free fatty acids comprised the largest percentage of these nonpolar lipids. Six uncommon (and as yet unidentified) fatty acids constituted the majority (51%) of both the free fatty acids and the fatty acids in TAGs of glyoxysome membranes; the same six uncommon fatty acids were < 7% of the acyl constituents in TAGs extracted from cotton-seed storage lipid bodies. TAGs of lipid bodies primarily were composed of palmitic, oleic, and linoleic acids (together 70%). Together, these three major storage fatty acids were < 10% of both the free fatty acids and fatty acids in TAGs of glyoxysome membranes.Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) constituted a major portion of glyoxysome membrane phospholipids (together 61% by weight). Pulse-chase radiolabeling experiments in vivo clearly demonstrated that C-14-PC and C-14-PE were synthesized from C-14-choline and C-14-ethanolamine, respectively, in ER of cotyledons, and then transported to mitochondria; however, these lipids were not transported to enlarging glyoxysomes. The lack of ER involvement in glyoxysome membrane phospholipid synthesis, and the similarities in lipid compositions between lipid bodies and membranes of glyoxysomes, led us to formulate and test a new hypothesis whereby lipid bodies serve as the dynamic source of nonpolar lipids and phospholipids for membrane expansion of enlarging glyoxysomes. In a cell-free system, H-3-triolein (TO) and H-3-PC were indeed transferred from lipid bodies to glyoxysomes. H-3-PC, but not H-3-TO, also was transferred to mitochondria in vitro. The amount of lipid transferred increased linearly with respect to time and amount of acceptor organelle protein, and transfer occurred only when lipid body membrane proteins were associated with the donor lipid bodies. H-3-TO was transferred to and incorporated into glyoxysome membranes, and then hydrolyzed to free fatty acids. H-3-PC was transferred to and incorporated into glyoxysome and mitochondria membranes without subsequent hydrolysis.Our data are inconsistent with the hypothesis that ER contributes membrane lipids to glyoxysomes during postgerminative seedling growth. Instead, the data support a novel source for glyoxysome (peroxisome) membrane lipids; lipid bodies, which house storage lipids that are converted to carbohydrate during heterotrophic seedling growth, also provide enlarging glyoxysomes with nonpolar lipids and phospholipids to accommodate membrane expansion. A working model depicting the origin and intracellular trafficking of membrane lipids for enlarging cottonseed glyoxysomes is presented.