Katagiri C, Sato M, Tanaka N
Biochemistry Laboratory, Hokkaido University, Sapporo, Japan.
J Biol Chem. 1987 Nov 25;262(33):15857-61.
The structure of lipophorin in insect blood (hemolymph) was investigated by a small-angle x-ray scattering method over the temperature range 0-45 degrees C. The small-angle x-ray scattering profile of lipophorin exhibited a symmetrical sphere with heterogeneous internal electron density. Cockroach and locust lipophorins, which contain hydrocarbons, demonstrated centrosymmetrical distribution of electron density inside the particles. A previous study suggested that the hydrocarbon-rich region is located in the core of lipophorin particle (Katagiri, C., Kimura, J., and Murase, N. (1985) J. Biol. Chem. 260, 13490-13495). Distance distribution functions, P (r), calculated for a simulated three-layer model (electron-rich shell, middle layer, and electron-deficient core) with radial electron density distribution, show good agreement with those observed experimentally for cockroach and locust lipophorins. The dimensions and electron density obtained for the middle layer reveal that this layer is occupied mainly by diacylglycerol and apolipophorin II. Thus, the present study together with previous reports strongly suggest that insect lipophorin is composed of centrosymmetrical three layers; an outer shell with apolipophorin I and phospholipid, a middle layer with diacylglycerol and apolipophorin II, and a core with hydrocarbons.
采用小角X射线散射法，在0至45摄氏度的温度范围内，对昆虫血液（血淋巴）中的脂蛋白结构进行了研究。脂蛋白的小角X射线散射图谱显示为一个内部电子密度不均一的对称球体。含有碳氢化合物的蟑螂和蝗虫脂蛋白，其颗粒内部电子密度呈中心对称分布。先前的一项研究表明，富含碳氢化合物的区域位于脂蛋白颗粒的核心部位（片桐，C.，木村，J.，和村濑，N.（1985年）《生物化学杂志》260，13490 - 13495）。根据具有径向电子密度分布的模拟三层模型（富电子壳层、中间层和缺电子核心）计算出的距离分布函数P(r)，与蟑螂和蝗虫脂蛋白的实验观测结果吻合良好。从中间层获得的尺寸和电子密度表明，该层主要由二酰基甘油和载脂蛋白II占据。因此，本研究与先前的报道有力地表明，昆虫脂蛋白由中心对称的三层组成：外层为载脂蛋白I和磷脂，中间层为二酰基甘油和载脂蛋白II，核心为碳氢化合物。
