Structure and Function of Lipophorin in Insect Blood

脂蛋白是一种广泛分布于昆虫体内的循环脂蛋白。脂蛋白作为一种可重复使用的穿梭机，在储存、合成和吸收部位与将脂类用作代谢燃料或结构成分的组织之间运输各种脂类。我们已经用小角X射线散射法提出了脂蛋白的三层模型：一个直径为168A的准球形颗粒，外层为24A的磷脂和载脂蛋白I(MR=2.5×10^5)，中间层为23A的二酰甘油和载脂蛋白II(MR=0.8×10^5)，以及一个核心(37A的碳氢化合物)。然而，关于脂蛋白转运脂质的机制却知之甚少。详细了解每种载脂蛋白的作用对于基本了解脂蛋白如何装载和卸载脂类，以及脂蛋白如何调节脂代谢是必要的。在本研究中，我们成功地分离了每一种现在试图被整合到脂质体中的载脂蛋白。这些重组的脂蛋白有助于进一步研究每个载脂蛋白在脂质运输中的作用。我们还成功地从脂蛋白颗粒中去除了二酰甘油，而不破坏脂蛋白本身。为此，真菌脂肪酶可用于降解脂蛋白中的甘油二酯。这将有助于理解脂质是如何卸载的。这些努力将开辟脂蛋白代谢的新领域。此外，我们在科罗拉多州土豆甲虫的血液中发现了一种富含二酰甘油的贫脂蛋白。这种缺乏甘油二酯的脂蛋白以前从未被报道过。纯化后，我们检测了其生理功能，并提出了其结构模型。

Lipophorin is a widely distributed circulating lipoprotein in insects. Lipophorin acts as a reusable shuttle to transport a variety of lipids between the sites of storage, synthesis and absorption, and the tissues that use lipids as metabolic fuel or as structural components. We have already proposed a three-layer model of lipophorin using a small angle X-ray scattering method ; a quasispherical particle of diameter 168A with an outer shell (24A of phospholipid and apolipophorin I (M_r = 2.5 x 10^5), a middle layer (23A of diacylglycerol and apolipophorin II (M_r = 0.8 x 10^5), and a core (37A of hydrocarbons. However, little is known about the mechanism of lipid transport by lipophorin. A detailed knowledge of the roles of each apolipophorin is necessary for a basic understanding how lipophorin loads and unloads lipid, and how lipophorin regulates lipid metabolism. In the present study, we succeeded in isolating each apolipophorin which is now tried to be incorporated into liposome. These reconstituted lipophorin contributes to further studies for understanding the roles of each apolipophorin in lipid transport. We also succeeded in removing diacylglycerol from a lipophorin particle without destroying lipophorin itself. For this purpose, fungal lipase was useful to hydrolyze diacylglycerol in lipophorin. This will help to understand how lipid is unloaded. These efforts will open a new field on lipoprotein metabolism. Furthermore, we found a hydrocarbon-rich diacylglycerol-poor lipophorin in the blood of a Colorado potato beetle. Such a diacylglycerol-poor lipophorin has never been reported before. After purification, we examined its physiological functions and proposed its structural model.