1987 Fiscal Year Final Research Report Summary
Structure of Lipophorin in Insect Blood
| Project/Area Number |
61540509
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
動物発生・生理学
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| Research Institution | Hokkaido University Institue of Low Temperature Science |
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Principal Investigator |
KATAGIRI Chihiro Hokkaido Univ. Inst. of Low Temperature Science, Research Associat, 低温科学研究所, 助手 (90002245)
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| Project Period (FY) |
1986 – 1987
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| Keywords | Insect Blood / Lipoprotein / Lipophorin / Diacylglycerol / Hydrocarbon / X線小角散乱法 |
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| Research Abstract |
Lipophorin is a widely distributed circulating lipoprotein in insects. It transports diacylglycerol, unesterified cholesterol and hydrocarbons, and 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 ad metabolic fuel or as structural components. Lipophorin forms a sphere-like particle of about 150 A diameter with a particle weight of about 6.0 x 10^5. It contains two apoproteins, apolipophorin I (M_r = 2.5 x 10^5-2.8 x 10^5) and apolipophorin II (M_r = 0.8 x 10^5) and 40 to 50% (w/w) lipid. In the present study, the structure of lipophorin was investigated by a small-angle X-ray scattering method over the temperature range 0 to 45 ゜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. 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.
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