Kawooya J K, Law J H
Department of Biochemistry, University of Arizona, Tucson 85721.
J Biol Chem. 1988 Jun 25;263(18):8748-53.
Lipid accounts for 40% of the dry weight of a mature Manduca sexta egg. Less than 1% of the total egg lipid is derived from de novo synthesis by the follicles. The remaining egg lipid originates in the fat body and is transported to the ovary by lipoproteins. Vitellogenin, the major egg yolk lipoprotein, accounts for 5% of the total egg lipid. The remaining 95% lipid is attributable to the hemolymph lipophorins, adult high density lipophorin (HDLp-A) and low density lipophorin (LDLp). When HDLp-A that is dual labeled with 3H in the diacylglycerol fraction and 35S in the protein moiety is incubated with follicles in vitro, the ratio of 3H:35S in the incubation medium does not vary and is similar to the ratio of the labels that are associated with the follicles. In an accompanying paper (Kawooya, J. K., Osir, E. O., and Law, J. H. (1988) J. Biol. Chem. 263, 8740-8747), we show that HDLp-A is sequestered by the follicles without subsequent hydrolysis of its apoproteins. These results, together with those presented in this paper, support our conclusion that HDLp-A is not recycled back into the hemolymph after it is internalized by the follicles and, therefore, does not function as a reusable lipid shuttle between the fat body and the ovary. When follicles are incubated with dual labeled LDLp, the diacylglycerol component of the particle is internalized by the follicles without concomitant endocytosis of its associated apoproteins. This LDLp particle is the major vehicle by which lipid is delivered to the ovary.
脂质占成熟烟草天蛾卵干重的40%。卵泡从头合成的脂质占总卵脂质的比例不到1%。其余的卵脂质起源于脂肪体，并通过脂蛋白运输到卵巢。卵黄原蛋白是主要的卵黄脂蛋白，占总卵脂质的5%。其余95%的脂质归因于血淋巴中的脂载脂蛋白，即成虫高密度脂载脂蛋白（HDLp-A）和低密度脂载脂蛋白（LDLp）。当在二酰甘油部分用3H和在蛋白质部分用35S进行双重标记的HDLp-A在体外与卵泡一起孵育时，孵育培养基中3H:35S的比例不变，且与与卵泡相关的标记比例相似。在一篇配套论文中（Kawooya, J. K., Osir, E. O., and Law, J. H. (1988) J. Biol. Chem. 263, 8740 - 8747），我们表明HDLp-A被卵泡隔离，其载脂蛋白随后不会水解。这些结果，连同本文所呈现的结果，支持我们的结论，即HDLp-A在被卵泡内化后不会再循环回血液淋巴，因此，它不作为脂肪体和卵巢之间可重复使用的脂质穿梭载体发挥作用。当卵泡与双重标记的LDLp一起孵育时，颗粒的二酰甘油成分被卵泡内化，而其相关载脂蛋白不会伴随内吞作用。这种LDLp颗粒是脂质输送到卵巢的主要载体。
