Katagiri C, Sato M, de Kort S, Katsube Y
Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan.
Biochemistry. 1991 Oct 8;30(40):9675-81. doi: 10.1021/bi00104a015.
The structure of lipophorin, isolated from hemolymph of the Colorado potato beetle, was investigated by differential scanning calorimetry (DSC) and small-angle X-ray scattering. The DSC heating curves of intact lipophorin showed endothermic peaks that were similar to peaks obtained with the hydrocarbon fraction isolated from this lipophorin. The observed peaks correlated with the transition of the hydrocarbons from an ordered into a more disordered state. Changes in structure of the lipophorin particles with increasing temperature were also observed by small-angle X-ray scattering studies. The structural organization of lipophorin was further elucidated by simulation analysis, using a three-layered symmetrical sphere as a model. These studies revealed that lipophorin from the Colorado potato beetle is a sphere with a maximum diameter of 175 A. The sphere is composed of three radially symmetrical layers of different electron densities. The outer layer (37.5-39.5 A in thickness) is composed of phospholipid, apolipophorin I, and part of apolipophorin II. The middle layer (5-10 A) contains diacylglycerol, the rest of apolipophorin II, and probably beta-carotene. The core of the particle (40-45 A) only contains hydrocarbons. This structure differs from another model, previously proposed for cockroach and locust lipophorins [Katagiri, C., Sato, M., & Tanaka N. (1987) J. Biol. Chem. 262, 15857-15861], in the small size of the middle layer. The volume of the middle layer correlated well with the low diacylglycerol content of this lipophorin.
通过差示扫描量热法（DSC）和小角X射线散射对从科罗拉多马铃薯甲虫血淋巴中分离出的脂磷蛋白结构进行了研究。完整脂磷蛋白的DSC加热曲线显示出吸热峰，这些峰与从该脂磷蛋白中分离出的烃类组分所获得的峰相似。观察到的峰与烃类从有序状态转变为更无序状态相关。通过小角X射线散射研究也观察到了脂磷蛋白颗粒结构随温度升高的变化。使用三层对称球体作为模型，通过模拟分析进一步阐明了脂磷蛋白的结构组织。这些研究表明，科罗拉多马铃薯甲虫的脂磷蛋白是一个最大直径为175埃的球体。该球体由三层具有不同电子密度的径向对称层组成。外层（厚度为37.5 - 39.5埃）由磷脂、脱辅基脂磷蛋白I和部分脱辅基脂磷蛋白II组成。中间层（5 - 10埃）含有二酰基甘油、脱辅基脂磷蛋白II的其余部分以及可能的β - 胡萝卜素。颗粒的核心（40 - 45埃）仅含有烃类。这种结构与先前针对蟑螂和蝗虫脂磷蛋白提出的另一种模型[Katagiri, C., Sato, M., & Tanaka N. (1987) J. Biol. Chem. 262, 15857 - 15861]不同，在于中间层的尺寸较小。中间层的体积与该脂磷蛋白中二酰基甘油的低含量密切相关。
